We now know it will be about Managing the Risk.
If just one Cell in a large Battery gets very ‘upset’ – like if it is damaged in a crash, if there’s a defect, or if it gets too hot, or soaked in water – it can short-circuit internally, start to cook, overheat and heat all its neighbouring cells, and the whole lot goes off, one after another, in a chain reaction of heat, fire and poisonous smoke. This is called ‘Thermal Runaway’. See Post #9 THERMAL RUNAWAY
THIS is the HAZARD, particularly for batteries bigger than a cell phone’s.
Maybe we should see what’s going on in a Li-ion Battery, and then we’ll have a better idea of the nature of the hazard?
But first, let’s quickly look inside a Lead-Acid Battery
– the batteries that still are used in motorcars. (You will realise that this is a VERY simplified description!)
Like any other, the battery has two terminals – it has a Positive and a Negative, and these are attached internally to two (or many more) ‘plates’ of Lead. They sit in a ‘bath’ of Sulphuric Acid diluted with water – Battery Acid. This is the Electrolyte. The bath is divided by a membrane which stops the Electrolyte mixing, but allows the electrically charged ions to pass through.
When fully Discharged – (‘we would call the battery ‘flat’) – both Lead plates, after reacting with the Sulphuric acid are coated with Lead Sulphate and that means that the acid now is mostly just water.
Connect to a source of Power – a Battery charger or Generator – and the charging current flowing through the battery reverses everything. It steals the Sulphate from the plates and turns it back into Sulphuric Acid, one plate becoming pure Lead and the other Lead Oxide.
When the external charging source is removed, and the battery is re-connected to a Load – a Starter Motor or a Light bulb, for example – the Chemical reaction is reversed again and the energy is given back as electricity.
The ‘take home’ is that the power in a Battery comes from Chemical energy.
If you want to make the Battery smaller and lighter, and more powerful you have to change the chemistry – which almost certainly will involve using more reactive ingredients to get more power from a smaller volume
– and THERE is the story of Lithium-ion batteries, and their safety.
The metal used is not Lead, which is one of the heaviest metals, and relatively cheap, but Lithium, which is the lightest of all metals (it floats on water). It also is highly reactive, where Lead is ‘relatively’ inert, but poisonous!
A Lithium-ion battery works the same sort of way as a Lead-Acid battery
– but the chemicals are a bit more complicated. One battery ‘plate’ the ‘Cathode’ is a sheet of Aluminium coated with a Lithium compound – like Lithium Iron Phosphate (which you don’t have to remember!). The other side of the battery, the Anode ‘Plate’ is Copper and Graphite.
Like the Lead Acid Battery, the Cathode and Anode plates are each sitting in a different Electrolyte – but these are complicated ‘soups’ of chemicals which include compounds of Lithium – like Lithium salts, and much more. When the Battery is being charged, the Lithium ions in the compound on the Cathode, and in the Electrolyte, ‘float’ off and migrate to the Graphite Anode where they land on, and ’Stick to’ the Graphite as Lithium ions. They have to pass through the plastic Separator (which the Li-ions can get through but the liquid electrolytes cannot). (Remember the Separators – they are very significant actors!)
Every ‘positively charged’ Lithium ion (Li+) has a corresponding Electron (e-) which also arrives to the Anode through an external conductor to “balance the books”. This flow of electrons in the conductor is the Electric Current which is the Charging current.
When a load is connected, the Lithium ions migrate back through the Separator to the Cathode causing their corresponding Electrons to flow round the external Conductor ‘back to’ the Cathode – this is the Electric current which does the work for us.
Actually there are many different combinations of chemicals being used and tested, with wide variations in cost, safety, storage capacity and charging rate and so on, but almost all of those use highly reactive chemicals. These are kept apart by the crucially important Separators – thin plastic films, porous to ions but not porous to the molecules of the Electrolyte.
If the battery is degraded in some way, the Separators may be pierced, there might also be damage that makes a short circuit between the plates, and heat also can cause chemical components of the Electrolytes to chemically react to produce gases. These cause the Battery to swell up.
The mixing of the gases, and certainly an internal short circuit, can produce enough heat to ignite the gases, which before, or after combustion can include Carbon Dioxide, Carbon Monoxide, Cyanide, Ethane, Ethylene, Hydrogen, Hydrogen Fluoride, Oxygen and more – most of which are highly reactive, flammable or poisonous.
The Take Away is that a Lithium-ion Battery fire is not ONLY about the fire
Efforts are made in the design of the Batteries to minimise the production of these gases, but every increase of safety might mean a reduction of performance. As the designs evolve, self-healing mechanisms and built in controls are being developed to maintain maximum performance and reduce the opportunities for degradation.
…. you might like to explore this further –
Go to – //breathebatteries.com/stories
A swollen battery is not a certain indicator that the battery is going to catch fire or explode immediately, but it is a very significant indicator that the Battery is not well and that it should replaced immediately. We will look at swollen batteries a bit more in the next Post – ‘REDUCE YOUR RISK’.
However, you will not be able to see your Batteries swelling in your EV, which makes it difficult to judge that there might be a problem. But statistically, the problem of battery failure in EV’s is very uncommon. It really only occurs if there is damage caused by an accident.
EV’s, generally speaking are made well and have many safety features to prevent them from going wrong. The surprising FACT, as we saw in our first Post, is that ICE’s (Internal Combustion Engine) vehicles actually are at least 60x more likely to catch fire than Electric Vehicles – (2023 Study Data – US National Transportation Safety Board & the Bureau of Transportation Statistics).
The figures below are Global Statistics from January to June 2023, gathered and presented by EV Firesafe – https://www.evfiresafe.com/ – a global authority on EV fires, and how to fight them.
It is difficult to see how we can Manage the already low RISK for our EV. It is much more important for us to Manage the RISK for the Li-ion Batteries that we find in our daily lives ….
The e-Scooters and e-Bikes are a major issue, as you saw in the graphic above, and cellphones, laptops, vapes, power banks and battery power tools, also can be hazardous. We will explore those soon, in later Blogs, where we will find that the Hazards are the same, if smaller, but the Risks are higher. But, understanding about HAZARD and RISK, as you do now, and having an idea about what is going wrong in a failing Li-ion Battery, you can better –
LEARN TO LIVE WITH LI-ION
In this Blog we talk about Lithium-ion Batteries as if they were one kind of a thing. They are not – there are at least, maybe six major different types of Li-ion Battery chemistry, with many different properties, that make them good for different purposes For our purposes now, we will think of them, and treat them as being all the same, and more or less potentially hazardous.
in Association with 
