Calculation of Short-Circuit Current in NCM Lithium-ion Batteries

1. Basic Concepts and Structure of NCM Lithium-ion Batteries

NCM lithium-ion batteries are high-performance batteries that offer high energy density, long cycle life, and good safety performance, making them widely used in electric vehicles, energy storage systems, and other fields. These batteries consist of a cathode, an anode, and an electrolyte, with the cathode material typically made of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA), among others. The combination of these materials enhances the energy density of the battery, making it advantageous in high-performance applications.

Compared to traditional lithium iron phosphate (LFP) batteries, NCM Lithium-ion Batteries provide higher voltage and energy density, resulting in longer usage time and higher power output. However, as their performance improves, the short-circuit current during a fault can also be higher, which requires accurate calculation and management of short-circuit currents to ensure battery safety.

2. Definition of Short-Circuit Current

Short-circuit current refers to the maximum current that a battery can output when it undergoes a short circuit (i.e., when the positive and negative terminals of the battery directly connect, forming a current loop). This parameter is crucial in assessing the safety performance of the battery because excessively high short-circuit currents can cause rapid heating, leading to battery damage or even dangerous events. Short-circuit current is an important indicator when evaluating the battery’s performance, especially during the design and use of the system.

3. Method for Calculating the Short-Circuit Current of NCM Lithium-ion Batteries

The short-circuit current of NCM Lithium-ion Batteries is influenced by the battery’s internal resistance, operating voltage, and maximum charge/discharge rate. The specific method for calculating it is as follows:

1. Measure the Internal Resistance of the Battery
   The internal resistance of the battery is a key factor in determining the short-circuit current. If the internal resistance is too high, the battery will generate significant power loss during discharge, reducing efficiency. It can be measured using a digital multimeter or a dedicated internal resistance tester. The unit of internal resistance is ohms (Ω), and while the value is typically small, it significantly impacts the short-circuit current.
2. Determine the Maximum Charge/Discharge Rate
   The maximum charge/discharge rate refers to the highest current the battery can safely charge or discharge at. The discharge rate is typically expressed in C (rate). For example, if the battery’s nominal capacity is 2000mAh, a 1C discharge rate corresponds to 2000mA, and a 2C discharge rate would be 4000mA.
3. Calculate the Short-Circuit Current
   Once the internal resistance and voltage are measured, the short-circuit current can be calculated using the following formula:Short-Circuit Current=Battery VoltageInternal Resistance\text{Short-Circuit Current} = \frac{\text{Battery Voltage}}{\text{Internal Resistance}}Short-Circuit Current=Internal ResistanceBattery Voltage​For example, if the NCM lithium-ion battery voltage is 3.7V and the internal resistance is 0.05Ω, the short-circuit current is:Short-Circuit Current=3.7V0.05Ω=74A\text{Short-Circuit Current} = \frac{3.7V}{0.05Ω} = 74AShort-Circuit Current=0.05Ω3.7V​=74AThis result indicates that the battery can output a current of 74A during a short circuit. Such a high current can cause rapid battery heating, damage, or even fire.

4. Safety Considerations in the System

While NCM Lithium-ion Batteries have high energy density and substantial output capacity, their larger short-circuit current also brings higher safety risks. When designing a battery system, it is crucial not only to calculate the short-circuit current but also to consider the rated current of the entire battery pack, its internal resistance, and external factors such as temperature and environmental vibrations. If the short-circuit current exceeds the system’s design capacity, it could lead to overheating and potentially hazardous situations such as fires or explosions.

To enhance system safety, designers typically implement the following measures:

1. Incorporating protective circuits (such as overcurrent protection and temperature protection) into the battery system.
2. Using high-quality Battery Management Systems (BMS) to monitor battery conditions and prevent overcharging or overdischarging.
3. Selecting battery materials with lower internal resistance to reduce heat accumulation.

5. Conclusion

NCM Lithium-ion Batteries offer high energy density and excellent charging/discharging efficiency. However, the larger short-circuit current poses a higher risk of battery damage during a fault. Therefore, it is essential to accurately calculate the short-circuit current and adopt protective measures to ensure the battery system’s safety and stability. Through proper design and safety management, we can fully utilize the advantages of NCM Lithium-ion Batteries while minimizing the associated risks.