Discussion on Preventive Measures for Thermal Runaway of Lithium Battery Packs

First, battery design optimization

1. Material selection

Cathode materials: Different cathode materials vary in thermal stability. For instance, lithium iron phosphate cathode materials have better thermal stability compared to lithium cobalt oxide and others. In high-temperature environments, lithium iron phosphate cathode materials are less likely to undergo decomposition reactions, releasing flammable gases such as oxygen, thereby reducing the risk of thermal runaway. Therefore, when designing batteries, the cathode materials can be reasonably selected based on the application scenarios and safety requirements.

Anode material: Graphite anode material is prone to form lithium dendrites during overcharging or high-current charging and discharging. When lithium dendrites grow to a certain extent, they may Pierce the separator, causing a short circuit between the positive and negative electrodes and triggering thermal runaway. Although silicon-based anode materials have a relatively high theoretical specific capacity, their volume changes significantly during charging and discharging, which can affect the cycle life and safety of the battery. R&d personnel can enhance the thermal stability and cycling performance of anode materials by modifying them, such as surface coating and doping.

Electrolyte: The electrolyte serves as the medium for ion transport within the battery, and its thermal stability is crucial to battery safety. Traditional electrolytes are prone to decomposition at high temperatures, generating flammable gases and organic acids, etc., which accelerates the occurrence of thermal runaway. The thermal stability and safety of the electrolyte can be enhanced by developing new electrolyte formulations, such as adding flame retardants and film-forming additives. Flame retardants can play a role in suppressing combustion before the electrolyte decomposes, while film-forming additives can form a stable protective film on the electrode surface, reducing the direct contact between the electrode and the electrolyte and lowering the risk of thermal runaway.

2. Structural improvement

Diaphragm design: The diaphragm is a key component that prevents short circuits between the positive and negative electrodes. The separator with thermal shut-off function is adopted. When the battery temperature rises to a certain level, the pores of the separator will automatically close to prevent the transmission of ions, thereby cutting off the chemical reactions inside the battery and preventing the further development of thermal runaway. In addition, the mechanical strength and thermal stability of the diaphragm can be enhanced by optimizing parameters such as the thickness and pore size distribution of the diaphragm.

Battery packaging: A reasonable battery packaging structure can effectively prevent the influence of external environmental factors on the battery and improve the battery's heat dissipation performance at the same time. For instance, batteries with aluminum-plastic film soft packaging have better flexibility and heat dissipation performance compared to those with metal casings. During the packaging process, it is necessary to ensure good sealing to prevent the leakage of the electrolyte and the entry of external moisture and air.

Second, optimization of the Battery Management System (BMS)

Precise monitoring

Temperature monitoring: Install high-precision temperature sensors at key locations within the battery pack, such as the surface of individual batteries and between battery modules, to monitor the temperature changes of the batteries in real time. BMS can promptly detect abnormal battery heating based on temperature data and take corresponding measures, such as adjusting the charging and discharging current and activating the cooling system.

Voltage monitoring: Precisely monitor the voltage of each individual battery to prevent overcharging or overdischarging. Overcharging can lead to an increase in internal pressure and temperature of the battery, while overdischarging can damage the structure of the battery's electrode materials, affecting the battery's performance and safety. When the voltage of a single cell deviates from the normal range, the BMS should promptly issue an alarm and take protective measures.

Current monitoring: Real-time monitoring of the charging and discharging current of the battery pack to ensure that the current remains within a safe range. High current charging and discharging will generate a large amount of heat inside the battery, accelerating the occurrence of thermal runaway. The BMS can reasonably control the charging and discharging power based on the current data to prevent battery overload.

2. Intelligent control

Charge and discharge management: Based on the battery's status and environmental conditions, formulate reasonable charge and discharge strategies. For example, in a high-temperature environment, reduce the charging current and the charging cut-off voltage to decrease the heat generation inside the battery. In a low-temperature environment, preheating the battery can enhance its charging and discharging performance as well as safety.

Balanced control: Due to the performance differences of individual cells in the battery pack, inconsistent voltages of individual cells may occur during the charging and discharging process. The BMS can discharge the individual cells with higher voltages and charge those with lower voltages through the balancing control function, keeping the voltages of each individual cell in the battery pack consistent and enhancing the overall performance and safety of the battery pack.

Fault diagnosis and Protection: The BMS should be equipped with a complete fault diagnosis function, capable of promptly detecting abnormal conditions of the battery pack, such as short circuits, open circuits, and leakage. When a fault is detected, the BMS should immediately take protective measures, such as cutting off the connection between the battery and external devices and activating the cooling system, to prevent the fault from further expanding and causing thermal runaway.

Third, use environmental control

1. Temperature control

Heat dissipation design: For high-power lithium battery pack applications, such as electric vehicles and energy storage systems, an effective heat dissipation system needs to be designed. Common heat dissipation methods include air cooling, liquid cooling and phase change material cooling, etc. The air-cooled heat dissipation system blows air over the surface of the battery pack through a fan to remove heat. The liquid cooling heat dissipation system uses coolant to circulate in the internal pipes of the battery pack, absorbing heat and transferring it to the external radiator for heat dissipation. The phase change material cooling system utilizes the property of phase change materials to absorb or release a large amount of heat during the phase change process to regulate the temperature of the battery pack.

Temperature range control: When using lithium battery packs, the ambient temperature should be kept within the suitable working temperature range of the battery as much as possible. Generally speaking, the optimal operating temperature for lithium batteries is 20℃ to 30℃. When the ambient temperature is too high, cooling measures should be taken, such as turning on air conditioners and adding cooling fans, etc. When the ambient temperature is too low, preheating treatment should be carried out, such as using a heating device to heat the battery pack.

2. Avoid mechanical damage

Installation and fixation: When installing the lithium battery pack, ensure it is firmly installed to prevent displacement or damage due to vibration or collision during use. The battery pack can be fixed on the equipment by using dedicated brackets and bolts. The strength and rigidity of the brackets must meet the requirements to withstand various forces during the operation of the equipment.

Protective measures: Install protective devices around the battery pack to prevent other objects from colliding with it. For instance, in electric vehicles, the battery pack is usually installed at the bottom of the vehicle. To prevent the battery pack from being damaged when the chassis is hit, protective plates can be installed around the battery pack.

Fourth, maintenance and inspection

1. Regular inspection

Visual inspection: Regularly inspect the appearance of the battery pack to check for any abnormal conditions such as bulges, deformations, or leakage. If any damage to the appearance of the battery pack is found, it should be repaired or replaced in a timely manner.

Inspection of connection points: Check the electrical connection points inside the battery pack, such as whether the connection between the battery terminals and the connection wires is firm, and whether there is any loosening, oxidation or other phenomena. Poor contact at the connection points can lead to an increase in resistance, generate heat, and accelerate the occurrence of thermal runaway.

2. Performance testing

Capacity testing: Regularly conduct capacity testing on the battery pack to understand its actual capacity and health status. When the capacity of the battery pack drops to a certain extent, it should be replaced in a timely manner to avoid the equipment from failing to work properly due to insufficient battery capacity and to reduce the risk of thermal runaway caused by battery aging.

Internal resistance detection: The internal resistance of a battery is one of the important parameters reflecting its performance and health status. An increase in internal resistance will cause the battery to generate more heat during charging and discharging, raising the risk of thermal runaway. By regularly testing the internal resistance of the battery, the aging condition of the battery can be detected in time and corresponding measures can be taken.