Lithium-ion battery is widely used in many electronic devices (smartphones, laptops, etc.) and electric mobility solutions (vehicles, bicycles, scooters etc.). However, the composition of lithium-ion technology can lead to safety risks that need to be considered. This is why it is important to use a Battery Management System (BMS) to optimise the safety of lithium-ion batteries.
How a Lithium-ion battery works
Lithium-ion batteries use lithium electrodes to store energy. They have become an essential part of powering everyday devices because of their high energy density and relatively long life.
The operation of a lithium-ion battery is based on the transfer of lithium ions between the electrodes when charging and discharging the battery. During charging, lithium ions move from the negative electrode to the positive electrode, storing energy in the battery. During discharge, the lithium ions move in the opposite direction, producing electricity to power the connected device or solution.
Lithium-ion batteries, however, can be sensitive to certain conditions internal and external to the battery that can cause thermal runaway.
Thermal runaway and lithium-ion battery
Thermal runaway is a phenomenon that occurs when a battery reaches an abnormally high temperature. This is manifested by the thermal runaway of a cell, which by propagation affects the temperature and operation of neighbouring cells and thus the battery.
There are many causes of thermal runaway in a cell, including:
- Internal failure of the cell (manufacturing defect, excessive mechanical stress, etc.)
- Overheating or exposure to excessive ambient temperature when the cooling system is insufficient
- Short circuit
Lithium-ion cells are particularly susceptible to overheating due to their chemical composition and high energy density. To prevent thermal runaway, it is therefore important to monitor the battery temperature in real time and take measures to control it. For this reason, the use of a Battery Management System (BMS) is essential for this type of battery.
The role of the BMS in optimising the safety of a lithium-ion battery
The role of the BMS can be grouped into 4 functions:
Collecting key data on the operation of the battery is the main functionality of the BMS. All its other actions to ensure the safety of the battery are based on the voltage, temperature and current values it obtains beforehand.
The measurement of the voltage as well as the other values is carried out by means of sensors in the BMS. The voltage must never be higher than the safe value range specified by the BMS manufacturer. Too high a voltage means overload, too low a voltage means over discharge;
Measuring the cell temperature is important to ensure the safety of the battery. Excessive temperature can lead to thermal runaway, too low a temperature can facilitate long-term cell degradation;
The battery is designed to supply and receive a maximum current according to the surrounding temperature. The battery is designed to supply and receive a maximum current according to the surrounding temperature. A current above this limit can cause the cells to overheat, accelerating their ageing.
Based on the measurements it takes, the BMS detects dangers or risks within the battery (overheating, overcharging, overcurrent, overvoltage or short-circuit) in order to protect it.
The BMS protection against overheating, for example, can be divided into 3 levels depending on the intensity of the risk:
- The first level of action of the BMS to prevent cell overheating is to balance their temperature during charging and operation;
- The second level of action is to reduce the power consumed or sent to the application powered by the battery;
- The third level of action is to stop the operation of the battery to avoid any risk of thermal runaway.
Managing and diagnosing
Another role of the BMS is to store the information it measures during battery operation. This information is essential to balance the energy stored in the battery to optimise its life and safety.
The BMS diagnoses the battery by estimating its state of charge (SOC), state of health (SOH), available power and maximum charge power.
The role of the BMS is to communicate with the electrical solution powered by the battery or any electronic device connected to the battery, such as a smart charger.
To do this, the BMS uses a communication protocol that allows it to transfer information such as the battery’s state of charge or the accepted charging power. In the context of a battery charger, this function of the BMS ensures that the battery is safely and optimally charged.
Thanks to this communication, the BMS also acts as an alarm in the event of a battery malfunction. The warning is given under two thresholds:
- Warning: The BMS warns that one of the battery operating conditions is approaching its safe operating limit by attempting to regulate the problem;
- Alert: The BMS informs that one of the battery operating conditions is critical before disconnecting it from the powered application or charger.
The BMS is a key element in ensuring the safety of lithium-ion batteries and monitors all the data provided by the battery, necessary for its operation.
The safety of your batteries is paramount at BMS PowerSafe. Whatever their electrochemistry (Lithium-ion, Ni-MH, Sodium-ion etc), we develop the safest and most suitable BMS for your lithium-ion battery.