Lithium-ion batteries are currently the most widely used in the battery industry. From mobile phones, computers, and iPads in the home appliance market, to new energy vehicles and cruise ships in the power field, to thermal batteries used in weapons and equipment, lithium-ion batteries are nowhere to be seen. Everywhere. However, lithium-ion batteries have unavoidable safety problems due to their structural characteristics and the nature of the materials used. For example, the strength and thermal stability of the separator between the positive and negative electrodes of a lithium-ion battery are not ideal, which can easily lead to a short circuit inside the battery; at higher temperatures, a strong exothermic reaction inside the battery will cause the temperature and internal pressure of the lithium-ion battery to increase ; The electrolyte and anode materials of lithium-ion batteries are flammable materials.

Especially in the power lithium-ion battery scene, due to the high total voltage and large working current required in the power field, it often requires thousands of single batteries to be used in groups. At this time, the safety problem of the battery becomes more prominent. . For example, Tesla's car battery pack uses thousands of lithium-ion battery cells. A large number of batteries are compactly arranged in a confined space. If some cells enter a thermal runaway state due to factors such as mechanical damage, thermal shock, internal short circuit, overcharge, etc., the temperature of the surrounding cells will also rise, and then the thermal runaway will occur. It spreads to the entire battery pack and eventually causes the disastrous consequences of overall combustion and explosion. As far as the current level of battery material technology is concerned, this safety issue has not yet been completely resolved. Therefore, heat insulation, flame retardancy, and fire protection of lithium-ion batteries are an effective means to reduce the harm caused by thermal runaway of lithium-ion batteries.

Aerogels are currently known solid materials with the lowest thermal conductivity. Products such as aerogel insulation felts, heat insulation panels, and heat insulation papers have up to 5 times the heat insulation performance of ordinary products, plus excellent fire and flame retardancy. , Soft, impact-resistant, sound insulation and noise reduction, etc., in addition to good promotion in the fields of industrial energy saving and civil insulation, with the development of the aerogel industry, the application of aerogel in the battery field has become more and more extensive.

01

Single cell aerogel thermal insulation protection

The thermal runaway of the single cell is the source of the thermal runaway of the entire battery pack. This is because when a single cell triggers the thermal runaway, it will produce a sudden increase in heat, and the amount of heat dissipation is much smaller than the heat produced, resulting in heat transfer to the surrounding cells , Which will quickly cause a large-scale thermal runaway of surrounding batteries, posing a safety hazard. Therefore, thermal protection between the cells is an effective means to eliminate the safety hazards of thermal runaway of the entire battery pack. The thermal protection between the cells is to add a heat insulation layer between the cells to block the thermal runaway from the uncontrolled single cell to the surrounding cells and reduce the damage to the battery pack and the incidental destructive effect.

The thermal insulation material between the single cells, as a kind of thermal protection material that can effectively delay or block the thermal runaway of the single cells to the entire battery system, must meet the following conditions:

a. Flame retardant (reaching V0 level)

b. Anti-aging, stable chemical properties;

c. Does not produce toxic gas;

d. Good elasticity, low thermal conductivity, waterproof, moisture-proof and vibration-proof;

e. Light weight, low price, thin thickness

At present, the commonly used thermal insulation materials include foam plastic, ultra-fine glass wool, high silica cotton, vacuum insulation board, aerogel, etc., the advantages and disadvantages of various thermal insulation materials:

Aerogel has extremely low thermal conductivity. Researchers have verified the thermal insulation and protection effect of aerogel insulation board between single cells through experiments. The aerogel separator was verified by the thermal runaway propagation experiment by wrapping the 6Ah capacity into a 20mm spacing module with four 200mm insulation materials, and adding a 1cm thick aerogel insulation board between the two monomers (Figure 1). The blocking effect of thermal runaway in the thermal protection of the single cell compartment.

The experimental results show that after monomer A has thermal runaway, the next monomer B in the blank group without thermal protection is quickly heated, and thermal runaway occurs. However, the maximum temperature of the experimental monomer B with an aerogel insulation board between the monomers is only 110 ℃, successfully blocked the thermal runaway propagation of the 6Ah cell at a distance of 20mm, and the voltage of the uncontrolled cell remained basically unchanged, which played a good role in protecting the safety hazards of the thermal runaway of the battery pack caused by the explosion of the single cell.

In addition, due to its excellent heat insulation and flame retardant properties, aerogels can further reduce the safety distance between monomers. In order to save more space and increase the total power of the battery pack, aerogel companies have developed a series of high-performance ultra-thin aerogel insulation panels, insulation paper and other products to meet the safety and high energy density needs of the battery industry.

Figure 1: Experimental installation diagram of a 1cm aerogel heat insulation board set up between the cells

Figure 2: Thermal runaway propagation blocking experiment with heat shields installed between cells. Comparison of cell temperature and blank group B cell temperature curve

02

Battery pack/box overall protection

Thermal runaway accidents of lithium-ion power battery packs occur from time to time. In addition to the protection of thermal runaway of lithium-ion power battery systems, thermal protection is also required between battery cells, battery modules, and between the battery box and the passenger compartment. Improve the thermal resistance of the thermal runaway cell to transfer heat to other battery systems, so as to achieve the purpose of hindering the spread of thermal runaway. In addition to excellent heat insulation, fire resistance, and flame retardant properties, aerogel felt also has the properties of softness, and can be cut and processed at will. It can be used for heat insulation protection between battery modules of different shapes, battery boxes and passenger compartments.

03

Aerogel protection for thermal batteries

Thermal batteries are widely used in the field of weapons due to their high discharge current density, long storage life, and resistance to environmental temperature during operation. From the EAP-12188 battery used in the emergency life-saving power supply of the JAS-39 light fighter, the GPS-9 battery on the global positioning long-range gun, the AN/SSQ-62 C battery on the sonar buoy, to all kinds of missiles and shells. To the shadow of the hot battery. The general operating temperature of a thermal battery is between 450"C~600"C, the entire discharge process depends on the initial heat "input", and the battery discharge life depends on the battery cooling rate and the battery's freezing temperature.

For long-life thermal batteries, the key issue is to have good insulation materials. Aerogel thermal insulation felt has ultra-low thermal conductivity, and the maximum operating temperature can reach 900-1100℃. The thermal battery thermal insulation cylinder made of aerogel material can be used as the thermal insulation layer of the thermal battery to perfectly solve the problem of aerospace and weaponry. Thermal batteries require high performance and long life.

With the development of my country's aerogel industry, the application of aerogel in the battery field will become more diversified, and the application range will also spread from the earliest military thermal batteries to more civilian battery fields, such as new energy power batteries, Thermal insulation and flame retardant protection for lithium-ion batteries and accumulators used in electronic equipment.