It is no secret that the electric and hybrid vehicle market is experiencing a high level of growth, particularly as consumers become more aware of global sustainability issues. Not only do electric vehicles help the environment, they are becoming more viable from a cost perspective. However, a common factor preventing consumers from purchasing fully electric vehicles (EVs) is ‘range anxiety’; barriers to entry include concerns about not being able to do long journeys, lengthy charging times and a lack of charging points and infrastructure.
To this end, automotive battery OEMs and manufacturers are pouring huge efforts into developing lithium-ion battery packs that can carry cars further and further, increasing the range to new heights. While range is important, thermal management of batteries is vital to the actual safety of the battery, vehicle and its occupants. This is due to the phenomenon of thermal runaway, a dangerous reaction that can occur in lithium-ion batteries.
What is Thermal Runaway?
Increasing the range of EVs can be done in multiple ways, from having larger battery packs with more modules and cells, to putting in higher energy density cells with higher capacity. However, all systems are susceptible to thermal runaway, some more so than others are.
Each cell in a lithium-ion battery contains a flammable liquid electrolyte. If the cell short-circuits, the electrolyte can combust and the pressure within the cell will rapidly increase until the cell vents the flammable electrolyte.
Temperatures at the ruptured cell can increase to above 1,000°C (1,832°F). Thermal runaway is the rapid and extreme rise in temperature and when it initiates the same reaction in adjacent cells, it is known as ‘thermal runaway propagation’.
When thermal runaway happens, it can produce smoke, fire and even explosions. Occupants need to have as much time as possible to escape the vehicle if it does occur. Since 2015, when the electric vehicle market really became mainstream, there have been many battery-related accidents that have been recorded.
Although thermal runaway is clearly life threatening, to date there is yet to be global regulation in place. Whereas China has implemented the GB/T 31485 standard, the UN has only proposed legislation. This leaves automotive manufacturers with the choice of whether they design their battery packs with systems designed to deal with thermal runaway incidents. It is up to their own risk assessment programmes to determine how likely thermal runaway is to occur.
Putting any protection in is likely to hinder the range capacity of the vehicle though – naturally, materials that are more protective equals less space for cells in a finite space.
Reaching, and going beyond, the middle ground, seemingly, there is no middle ground between the two. However, it does not need to be the case that battery manufacturers compromise safety for range, or vice versa.
Windsor-based Morgan Advanced Materials is a global material engineering company, which designs and manufactures a wide range of high specification products with extraordinary properties, across multiple sectors and geographies the business has been significantly researching and developing a range of thermal management protection materials and methods over many years.
These can provide more time for occupants to exit a vehicle, while the dissipation of heat lessens the chance of thermal runaway spreading uncontrollably.
It is not a ‘one-size-fits-all’ approach though. Every battery design is different, and so the protection method must be unique. There are three levels of protection that engineers can design into their systems to significantly reduce the impact of thermal runaway in electric vehicles: cell-to-cell, module-to-module, and battery pack level.