Lithium ion batteries come in many forms and shapes and are increasingly all around us - from mobile phones to electric cars. For this reason, growing attention is being turned to their safety and to the consequences that damages, overheating, and overcharging can have. A significant concern is the risk of thermal runaway, when the battery starts to become so hot that it spontaneously combusts or explodes. This represents a fire hazard, but also releases toxic gases and particles which can be harmful to people or the environment.
Understanding the nature of those particles and gases, and in which quantities they are released, is essential to establish safety standards and protect users. Thanks to the battery testing capabilities of our sister brand CamMotive, we investigate the release of particles during the thermal runaway of lithium ion batteries.
Thermal runaway can be induced by externally heating or overcharging the batteries (two common real-life scenarios) and monitoring the voltage, current, and cell temperature during the process can give early indicators about the battery health.
The particles released by the explosion of an overcharged single LiPo cell were captured by an extract and measured using the Cambustion Fast Aerosol Sizer DMS500 to provide real-time nanoparticle size distributions between 5 and 1000 nm. Using the DMS500's concentration data, and combined with measurement of the total flow through the extract, the DMS500 data can give information about the total number and total mass of particles released by each explosion event.
A peak of 4.5e13 particles/s is captured in the data below. For comparison, the current Euro 6 legislation limits particle emissions from light vehicles to 6e11 particles/km, corresponding to 1e10 particles/s when driving at 60 km/h. The burst of particles released by the explosion is several order of magnitudes more intense than a typical urban source, and generates as many particles overall as driving in a Euro 6 vehicle for over 200 km.
The vast majority of the particles are released over just 15 seconds; this requires instruments capable of resolving very fast transients, and Cambustion analysers are uniquely suited to capture these rapid sub-second complex events. Even if a clear peak in emissions is shown by the total number, the particle size information recorded by the DMS500 offers unique insights into the complexity of the explosion, with rapid evolution of the aerosol visible as the combustion proceeds.
Collection of material for chemical analysis, combined with size distributions from the DMS500, can inform models regarding aerosol dispersion, dosimetry and health effects.
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