How does the battery thermal runaway monitoring system prevent the battery thermal runaway accident?

        The detection of gas concentration in the early stage of battery pack by battery thermal runaway monitoring system is an important means to prevent battery thermal runaway accidents.

        First，The principle of gas generation is related to thermal runaway

        1. Hydrogen (H₂)

        During the operation of the battery, especially in lithium-ion batteries, hydrogen gas is produced when the electrolyte inside the battery breaks down. For example, in the case of overcharging or internal short circuit of the battery, the positive and negative electrode materials of the battery may react abnormally with the electrolyte. For lithium-metal batteries, lithium reacts with organic solvents in the electrolyte to produce hydrogen. When the hydrogen concentration begins to rise, this is often a serious side reaction occurring inside the battery, which may be a prelude to thermal runaway. Because the production of hydrogen is usually accompanied by a large amount of heat release, and hydrogen itself is a flammable and explosive gas, its accumulation will increase the risk of battery explosion.

        2. Carbon Dioxide (CO₂)

        The production of carbon dioxide is also related to chemical reactions inside the battery. When the negative electrode material of the battery (such as graphite) is under high temperature or abnormal electrochemical reaction, it may react with some components in the electrolyte to produce carbon dioxide. In addition, during the thermal runaway process of the battery, the combustion of organic components such as the battery housing material or the diaphragm inside the battery will also produce carbon dioxide. If the concentration of carbon dioxide is increased, it indicates that the chemical reaction inside the battery has gone beyond the normal range, possibly due to the battery overheating or internal short circuit, which is an important signal that the battery thermal runaway is developing.

        3. Carbon Monoxide (CO)

        Carbon monoxide is usually produced by incomplete combustion of organic components inside batteries or some complex chemical reaction. For example, carbon monoxide may be produced when the battery separator breaks down with heat or when the organic solvent in the electrolyte breaks down at high temperatures. Carbon monoxide is a toxic gas, and its appearance means that there has been a more serious thermal runaway inside the battery, which may be caused by the battery being in a high temperature environment for a long time or suffering a serious external impact.

        Second, the principle of gas detection technology

        1. Electrochemical sensor

        Electrochemical sensor is one of the common techniques for detecting gas concentration. For hydrogen detection, it uses hydrogen to undergo oxidation reaction on the electrode surface of the electrochemical sensor to generate a current signal. According to Faraday's law, the current generated is proportional to the concentration of hydrogen. This sensor has high sensitivity and good selectivity, and can send alarms at low hydrogen concentration.

        For the detection of carbon monoxide and carbon dioxide, electrochemical sensors are also based on their electrochemical reactions at the electrode surface. The carbon monoxide is oxidized on the sensor's working electrode, and the carbon dioxide reacts with the electrolyte in the sensor to produce the corresponding electrical signal, thus achieving accurate measurement of the concentration of these two gases.

        2. Infrared absorption spectroscopy

        Infrared absorption spectroscopy is based on the absorption characteristics of different gas molecules to specific wavelengths of infrared light. Carbon dioxide and carbon monoxide have characteristic absorption peaks in infrared band. For example, carbon dioxide has a strong absorption peak near 4.26μm, and carbon monoxide has an absorption peak around 4.6μm. By emitting infrared light and detecting the change in light intensity after being absorbed by the gas, the concentration of the gas can be calculated. This technology has the advantage of high precision, non-contact, rapid and accurate measurement of gas concentrations, and can detect multiple gases simultaneously.

        3. Semiconductor gas sensor

        Semiconductor gas sensors use the principle that certain metal oxide semiconductors (such as SnO₂, ZnO, etc.) change their electrical properties (such as resistance) after adsorbing gas molecules. For hydrogen detection, when hydrogen molecules are adsorbed on the semiconductor surface, the resistance of the semiconductor will decrease. By measuring the change in resistance, the concentration of hydrogen can be determined. For carbon monoxide and carbon dioxide, there are similar detection mechanisms based on the change of electrical properties caused by the interaction of semiconductor materials with gases, but their selectivity is relatively weak, and other techniques are needed to improve the detection accuracy of specific gases.

        Third，Early warning and control strategy based on gas concentration detection

        1. Set the alarm threshold

        According to the battery type, capacity, working environment and other factors, set different gas concentration warning thresholds. For example, for hydrogen concentration, when a certain volume fraction (such as 0.1-0.5%) is reached, the system will issue a level one warning, indicating that the battery may have potential safety hazards. For carbon monoxide and carbon dioxide, thresholds are also set depending on the degree to which they are associated with thermal runaway of the battery. When the concentration of carbon monoxide reaches a certain level (such as 50ppm to 100ppm) or the concentration of carbon dioxide exceeds a certain range (such as 1%-2%), the system will determine that the safety condition of the battery is deteriorating.

        2. Hierarchical response measures

        When the gas concentration exceeds the alarm threshold, the system takes corresponding response measures. In the first warning stage, simple ventilation measures may be initiated to expel the air containing a high concentration of gas from the battery compartment, while reducing the battery's charge and discharge power to see if the battery status can return to normal.

        If gas concentrations continue to rise, reaching a level two alert or higher, the system will take more aggressive measures. For example, emergency cut off the battery's charge and discharge circuit, start the cooling system, and even notify the relevant personnel for emergency evacuation to avoid serious consequences caused by the battery's thermal runaway, such as fire or explosion.