With the strong support for the development of new energy vehicles, the number of electric vehicles is increasing rapidly, and the pace of industrialization is accelerating. At present, electric vehicles mainly use lithium-ion batteries as power batteries. After years of development, the safety of lithium-ion power batteries has been significantly improved, but under extreme conditions, lithium batteries still have the risk of combustion and explosion. The application of aerogel materials will further strengthen the fire protection requirements of power batteries and ensure the safety of people's lives and property.
The main power source of new energy vehicles comes from the power battery system, which determines the driving ability, safety performance and life of new energy vehicles. Especially, all power of pure electric vehicles comes from its battery system. Power battery system generally consists of battery module, Battery Management System BMS, thermal management system and some electrical and mechanical systems. The power battery module is composed of several to hundreds of battery cells in parallel and in series. Under different driving conditions and environments, the single cell will produce certain heat while outputting electric energy due to its own resistance, which makes its own temperature higher. High temperature working environment and fierce collision are the two biggest culprits that destroy lithium-ion battery and cause battery combustion and explosion. A large amount of heat generated by power battery system in the working process is gathered in the narrow battery box. If the quantity of heat can’t be quickly dissipated in time, the life and performance of battery module will be greatly influenced, which even leads to fire and explosion Therefore, the domestic thermal management of new energy power battery system pays more attention to the mechanism and characteristics of thermal runaway in heat dissipation and monomer level. Little attention is paid to the high-efficiency heat insulation and flame retardant and thermal runaway protection between cells. However, when a single cell is out of control, the heat production increases sharply, and the heat dissipation is far less than the heat production. The heat transfer to the surrounding cells will quickly lead to a large-scale thermal runaway of the surrounding cells, forming a potential safety hazard caused by the thermal runaway level triggered by the thermal runaway of the single cell and then spread to the whole battery system. Therefore, it is necessary to add heat shield between the battery cells to slow down the spread speed of heat runaway, and take further fire-fighting measures to win time.
In recent years, aiming at the problem of thermal runaway propagation of battery pack, the thermal runaway propagation from runaway monomer to the surrounding is blocked by adding an insulating layer in the battery pack, so as to reduce the damage of battery pack and its collateral damage. At present, thermal insulation materials commonly used in power batteries include foam, plastic foam, ultra-fine glass wool, high silica oxygen cotton, vacuum insulation board, silica aerogel, etc. the insulation board inside the battery pack is placed between the single cell cores, which can effectively delay or block the thermal control equipment of the single core heat runaway to the entire battery system. The following performances are required:
1. Flame retardant and high temperature resistant.
2. Low thermal conductivity.
3. No toxic gas
4. Waterproof, moistureproof and shockproof
5. Light weight, low price and thin thickness.
Foam is a kind of foamed material with the characteristics of elasticity, light weight and heat insulation. There are many kinds of foam, such as PU, PE, Cr, Eve foam, etc. Pu, XPE and IXPE foam can be used for thermal insulation between power battery cells. PU foam still has very good resilience under time pressure, which is suitable for the insulation and shockproof material of soft battery cell. However, when PU foam burns, it will release toxic gases, so it is not suitable for pure electric or plug-in hybrid electric vehicles and other new energy vehicles. XPE foam is made by adding chemical crosslinking agent to produce foam after chemical crosslinking. The main characteristics of XPE foam are good performance, large cell, and the thickness of the product is generally more than 3mm. IXPE foam is a kind of foam product after irradiation crosslinking. Its main characteristics are fine cell, beautiful appearance, excellent performance, and good environmental protection performance. It can meet the European Union's testing standard. It is a very suitable thermal insulation material for power battery. However, due to the expensive irradiation equipment and poor ray penetration, this method is not suitable for preparing thick foams. Secondly, based on the characteristics of PE material itself, it will soften or deform greatly at 120 ℃, and it can not play a good flame retardant role when the core is in danger of ignition. The thermal insulation method of the battery thermal management system of General Motors volt is to place foam between the cell and the cell. However, through the analysis of the structure of the volt module, the foam used does not appear the phenomenon of self extinguishing, which means that it is not V0 required by the national standard.
Silica aerogel is a porous solid material with dispersed medium as gas. It is the lightest solid material used in engineering at present. The thermal conductivity of aerogel felt made of it is 0.020 W/ (M. K) or even lower, and has super hydrophobic, A1 grade flame retardant, wide temperature range (-200~650 C), long life, compression resistance and non-toxic. Compared with traditional thermal insulation materials, aerogel material thickness is only 1/2-1/5 of traditional thermal insulation materials under the same heat insulation effect. Based on the above characteristics of aerogels and the demand of power battery insulation panels, gas condensate film is considered to be the thinnest and most efficient thermal insulation material for new energy vehicles and power batteries.
Left: aerogel film for power battery insulation Right: heat insulation foam for power battery.
| FRM-A-600 aerogel material | IXPE foam |
Density (kg / m3) | 200 | 200 (5 times foaming) |
Thermal conductivity (w / MK) | 0.017 | 0.095 |
Service temperature (℃) | -200~600℃ | -60~120℃ |
Flame retardancy | Building A1/UL94V0 | UL94HB |
Water absorption 24h at room temperature (%) | ＜1% | <0.2 |
Environmental protection and non toxicity | ROHS standard | ROHS standard |
Tensile strength (MPa) | 0.4 | Transverse > 1.3, longitudinal > 1.5 |
Elongation at break (%) | 8.53 | 200 |
Normal thickness（mm） | 0.5/1/2/3/6/10 | 0.5/1/3/10 |
When the aerogel insulation board is used in lithium ion power battery module, the low thermal conductivity can effectively block the heat diffusion caused by the charge and discharge of the core at high magnification. When the core is out of control, it can play a role of thermal insulation and delay or block the accident. When the core is overheated and burned, the aerogel insulation board can effectively block the performance of building grade a non combustible. Delay the spread of the fire and provide enough time for escape. Therefore, the gas film insulation board can play a very important role in improving the safety performance of new energy vehicle power battery pack.
Tesla has designed a kind of insulation board made of heat insulation material and elastic material in its patent of lithium-ion battery pack, which is placed between different cell lines of the battery module, so as to block the runaway heat transmission between adjacent cells. In the research on thermal protection and heat dissipation integration of vehicle power battery, the thermal conductivity is about 0.020. Taking the square ternary lithium-ion battery as the object, the simulation model of the battery pack is established, and the integrated thermal management scheme of alternately placing the heat shield and heat pipe in the battery pack is proposed, which can not only improve the heat dissipation capacity of the battery pack, improve the uniformity of the internal temperature distribution of the battery pack, but also greatly prolong the thermal runaway propagation time and improve the operation safety performance of the battery pack . Secondly, by increasing the thickness of the heat shield from 1 mm to 2 mm, the runaway heat transmission can be completely blocked.
Market prospect of gas film insulation board
The electric vehicle industry has entered the growth period from the cultivation period. According to the medium and long term development plan of the automobile industry compiled by the Ministry of industry and information technology and the calculation of BOC securities, it is estimated that the overall production and sales will be 2 million in 2020; the medium and long term development plan of the automobile industry also specifies that by 2025, the sales volume of new energy vehicles will account for more than 20% of the total sales volume. If the national car sales reach 35 million in 2025, the new energy vehicles will be equivalent to the expected sales of 7 million. With the development of new energy vehicles, people pay more and more attention to the safety performance of new energy vehicles. Although aerogel insulation is higher than traditional foam insulation material, its safety performance is much higher than that of traditional insulation material. It is generally recognized as the best power battery thermal insulation and flame retardant material. Therefore, aerogel insulation film is undoubtedly the best choice for electric buses and high-grade new energy cars with higher safety requirements. With the maturation of aerogel materials and the expansion of production scale, the price will inevitably drop. The application and market penetration of new energy vehicle power battery will also increase sharply with the growth of new energy vehicle industry.
Aerogel materials in the field of new energy vehicles, in addition to the heat insulation and flame retardancy between the power battery cores, can also be applied to the thermal insulation and shock proof modules between the shells, the external cold proof layer and the high-temperature insulation layer of the battery box.
This article is from China's aerogel official account.
