Analysis of Explosion-proof Design Principles for Lithium Battery Packs

First, the foundation of explosion-proof design - understanding the causes of lithium battery pack explosions

The explosion of lithium battery packs is essentially an extreme manifestation of thermal runaway, which is often triggered by factors such as internal short circuits, overcharging, overdischarging, and external mechanical damage.

Internal short circuit: During the production process of the battery, metal impurities may be mixed in, or during use, lithium dendrites may grow and Pierce the separator, causing the positive and negative electrodes to come into direct contact, generating a huge current instantly and causing the battery temperature to rise sharply. Just like a wire directly connected to the positive and negative terminals of a power source, without resistance limit, the current will be infinitely large, and the battery will also release a large amount of heat due to short circuit inside.

Overcharging: When the charging voltage or current of a battery exceeds the specified value, the positive electrode material will over-delithiate, making its structure unstable. At the same time, lithium metal will precipitate from the negative electrode, forming lithium dendrites. Moreover, when the electrolyte is overcharged, it will also undergo decomposition reactions, generating gases and heat, which further promotes the occurrence of thermal runaway. For instance, when the battery is fully charged, charging should be stopped. However, if the charging equipment malfunctions or is not properly controlled and charging continues, it will cause overcharging problems.

Over-discharge: Excessive discharge can damage the electrode material structure of the battery and increase its internal resistance. When recharged, more heat will be generated inside the battery, increasing the risk of thermal runaway. Just like a person who is already overworked, if they continue to work at a high intensity, various problems will arise in their body.

External mechanical damage: When the battery pack is subjected to external forces such as squeezing, collision, or puncture, it may cause the battery casing to crack and the separator to be damaged, thereby triggering short circuits and thermal runaway. For example, when an electric vehicle undergoes a severe collision, the battery pack may be damaged due to a huge impact.

Second, the core of explosion-proof design - multi-level protection mechanism

(1) Protection at the individual battery level

Material selection and modification

Cathode material: Select cathode materials with good thermal stability, such as lithium iron phosphate. It has a relatively stable structure at high temperatures and is not prone to decomposition to produce flammable gases such as oxygen, reducing the possibility of explosion caused by thermal runaway. In contrast, materials such as lithium cobalt oxide are more prone to decomposition at high temperatures and have poorer safety.

Anode material: Modifying the anode material, such as coating it with a protective film on the surface, can inhibit the growth of lithium dendrites and reduce the risk of internal short circuits. Meanwhile, select the appropriate anode material formula to enhance its cycling stability and thermal stability.

Electrolyte: Develop new electrolyte formulas and add flame retardants, film-forming additives, etc. Flame retardants can suppress combustion before the electrolyte decomposes, and 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 probability of thermal runaway.

Structural design optimization

Separator design: A 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, parameters such as the thickness and pore size distribution of the diaphragm can be optimized to enhance its mechanical strength and thermal stability.

Battery packaging: Use high-strength and well-sealed packaging materials to prevent electrolyte leakage and the entry of external moisture and air. Meanwhile, a reasonable packaging structure can enhance the battery's resistance to mechanical damage and reduce the risk of short circuits caused by external impacts.

(2) Protection at the battery pack level

Electrical isolation and protection

Fuses and circuit breakers: Fuses and circuit breakers are installed in the circuit of the battery pack. When the current exceeds the set value, the fuse will blow and the circuit breaker will trip, cutting off the circuit to prevent overcurrent from causing the battery to overheat and explode. This is similar to the fuses and air switches in household circuits, which play a role in protecting the safety of the circuit.

Battery Management System (BMS) : BMS is a key component in the explosion-proof design of battery packs. It can monitor parameters such as voltage, current, and temperature of the battery in real time. When abnormal conditions are detected, such as excessively high or low voltage of individual batteries or excessively high temperature, the BMS will promptly take measures, such as adjusting the charging and discharging current, activating the cooling system, and cutting off the connection between the battery and external devices, to ensure that the battery pack operates within a safe range.

Heat dissipation design

Air cooling: Air is blown over the surface of the battery pack by a fan to remove heat. This method has a simple structure and low cost, and is suitable for battery packs with smaller power. However, the heat dissipation efficiency is relatively low, and it may not be able to meet the heat dissipation requirements for high-power battery packs.

Liquid cooling heat dissipation: By circulating the coolant in the internal pipes of the battery pack, it absorbs heat and transfers it to the external radiator for heat dissipation. Liquid cooling has a high heat dissipation efficiency and can quickly lower the temperature of the battery pack, but the system is complex and the cost is relatively high.

Cooling of phase change materials: Phase change materials can absorb or release a large amount of heat during the phase change process. When phase change materials are filled in the battery pack, when the battery temperature rises, the phase change materials absorb heat and undergo phase change, thereby playing a cooling role. This approach has better temperature uniformity, but the cost and durability of phase change materials are issues that need to be considered.

Mechanical protection

Battery pack casing: The battery pack casing is designed to be sturdy, made of high-strength metal or composite materials, capable of withstanding certain external impacts and compressions, protecting the internal battery cells from damage. The shell should also have good sealing performance to prevent moisture, dust and other substances from entering.

Buffer structure: Buffer structures such as foam and rubber are set up inside the battery pack. When the battery pack is impacted, the buffer structure can absorb energy, reduce the force on each battery cell, and lower the risk of mechanical damage.

(3) System-level protection

Fireproof and explosion-proof isolation: The battery pack is installed in an independent fireproof and explosion-proof cabin, which is constructed with fireproof and explosion-proof materials and equipped with a ventilation system and pressure relief device. When the battery pack experiences thermal runaway, the fireproof and explosion-proof compartment can prevent the spread of fire and explosion shock waves, protecting the safety of surrounding equipment and personnel.

Fire protection system: Install fire protection systems such as gas fire extinguishing systems and water spray fire extinguishing systems around the battery pack. When a fire is detected, the fire protection system can be activated in time to extinguish the flames and prevent the fire from spreading.

Third, verification and continuous improvement of explosion-proof design

(1) Test verification

Safety performance testing: A series of safety performance tests are conducted on the battery pack, such as overcharge test, overdischarge test, short circuit test, compression test, needle-puncture test, etc., to simulate various extreme situations and verify the explosion-proof performance of the battery pack. Only through strict testing can the safety of the battery pack be ensured in actual use.

Environmental adaptability testing: Considering the usage of the battery pack under different environmental conditions, conduct environmental adaptability tests such as high temperature, low temperature, and damp heat to verify the explosion-proof performance and reliability of the battery pack in various environments.

(2) Continuous improvement

Data analysis and feedback: Collect data of the battery pack during actual use, such as charging and discharging records, temperature changes, fault information, etc. Through data analysis, identify potential safety hazards and design deficiencies, providing a basis for the improvement of explosion-proof design.

Technological innovation and application: Focus on the cutting-edge development of lithium battery technology, continuously introduce new materials, processes and technologies, and constantly improve and innovate the explosion-proof design of battery packs to enhance their safety and performance.