Thermal insulation materials need to have the following properties:
① Flame retardant and high-temperature resistant;
② Low thermal conductivity;
③ Does not produce toxic gases;
④ Waterproof, moisture-proof and shock-proof;
⑤ Light in weight, low in price and thin in thickness.
1)Flame-retardant foam: Flame-retardant foam is low in price, highly flexible, and offers high flexibility in size design, but its flame-retardant temperature is relatively low. Flame-retardant foam materials come in a variety of types, have good product resilience, and a high degree of customization. They offer high design flexibility in lithium battery PACK solutions. However, due to their shortcomings in fire resistance, impact resistance, and heat insulation compared to aerogel felt and mica materials, their application proportion has gradually decreased. Currently, they are mainly used as buffer sealing materials between modules and around battery packs. In the future, it may be partially replaced by new materials such as mica composite materials and ceramicized silicone foam.
2) Aerogel materials: Aerogel composite materials are currently the most widely used and best-performing flame-retardant and heat-insulating materials for lithium batteries. Aerogel composite materials feature excellent flame retardant and heat insulation performance as well as low usage. They are regarded as the thinnest and most efficient thermal insulation materials for new energy vehicle power batteries and have become the best choice for thermal insulation materials of lithium battery cells. Currently, their penetration rate is approximately 20% to 30%, making them the most widely used flame retardant and heat insulation materials for lithium batteries. Compared with other materials, aerogel composites have the advantages of superhydrophobicity, V0 flame retardancy, wide operating temperature range, low thermal conductivity, long service life, light weight and non-toxicity. Under the same heat insulation effect, the thickness of aerogel materials is only 1/5 to 1/2 of that of traditional thermal insulation materials. It has excellent heat insulation performance. Currently, the technology of no thermal spread in power batteries has become a requirement for thermal runaway protection in high-end models. In the future, it is expected to be popularized from ternary models to more medium and high-end lithium iron phosphate models. Aerogel felt is a composite of silica aerogel powder and glass fiber cotton. It can withstand 1000°C for a short time and has a certain heat insulation effect. However, batteries expand during charging and discharging. Aerogel felt has no resilience and cannot absorb the battery's expansion. Long-term use can cause excessive internal pressure in the battery cells, leading to a decline in cycle life. At the same time, the mass production process of aerogel is high-temperature and high-pressure, and the patent is held by an American company, which poses risks of high cost and unstable supply.
3) Flame-retardant potting compound ：Flame-retardant potting compound is the main choice for fireproof, flame-retardant and heat-insulating materials for cylindrical batteries. With the development of vehicle models towards lightweight, low-density and high-strength flame-retardant potting compound will be the direction of technological upgrade in the future.
4) Ceramicized silicone rubber ：composite materials are currently used in a relatively small proportion, mainly as "fireproof brackets" between the module and the upper cover plate. Due to the high application cost, only a few mid-to-high-end models have a small amount of application at present. With product upgrades and cost reduction, the application scope is expected to expand in the future.