A recent increase in lithium battery fires has sparked safety concerns; however, the lithium category covers a vast number of chemistries – not all of which are created equal.
Lithium batteries are a key component in Australia’s energy transition. Their high energy density and lightweight properties make them ideal for large-scale energy storage and electric vehicles, but this technology has also seen its fair share of controversy surrounding safety.
So, how can the energy sector utilise this technology without risk of disaster? To find the answer, Energy turned to R&J Batteries Energy Storage Manager, Justin Skaines, for advice.
Mr Skaines explained that the term ‘lithium’ refers to a very broad category of batteries.
“People assume that the main component of the battery is lithium, but that couldn’t be further from the truth – normally between two and seven per cent of the battery is actually lithium, and it’s the transfer of lithium ions from the positive to the negative plate within the battery that gives them their name,” Mr Skaines said.
“As lithium is such a small part of the battery itself, this means that there are a lot of other elements in the batteries that define their performance and what their role can be.”
There are six main families of lithium batteries: lithium nickel manganese cobalt, lithium nickel cobalt aluminium oxide, lithium cobalt oxide, lithium manganese oxide, lithium titanate (Li₂TiO₃) and finally, lithium iron phosphate (LiFePO₄).
The use of nickel, manganese or cobalt in the positive plate of these batteries increases their susceptibility to thermal runaway, which is the main cause of a battery fire. However, these rare earth materials are not used in two of these families: Li₂TiO₃ and LiFePO₄.
Mr Skaines said that five of the six families have a carbon or graphite negative plate, however Li₂TiO₃ batteries have titanium oxide negative plate, which means that thermal runaway is not an issue at all for this battery.
“They’re really the safest of the lithium technologies, but the biggest downside of those batteries is they’re a lot more expensive upfront and they’re not as energy dense, so you need a bigger battery to get the same energy.”
Alternatively, LiFePO₄ batteries offer more balance between cost‑effectiveness, safety and functionality.
“The main element in the positive plate of the battery is phosphate, and the reason for this is that it’s mechanically and chemically stable – which means that they’re less susceptible to thermal runaway,” Mr Skaines said.
Thermal runaway occurs when a battery gets too hot, either as a result of a faulty charge or external conditions. Mr Skaines said that most lithium batteries with a graphene negative plate are unable to dissipate that heat quickly enough, which causes flammable gases to build up as the heat increases. Those gases then ignite and create a self-maintaining fire that is very difficult to extinguish.
“LiFePO₄ batteries have a higher tipping point compared to other graphene or carbon plated batteries, which means that they’re more resilient in high temperatures and more resistant to overheating,” Mr Skaines said.
Inside the box
Despite their wide temperature range, there is still a chance that thermal runaway can occur in an LiFePO₄ battery. To combat this, most modern cells include a BMS (battery management system), which actively monitors the temperature and voltage during operation and will disconnect the battery when certain trigger points are reached – preventing dangerous faults from occurring.
Mr Skaines said that the quality of the BMS is a crucial factor when it comes to safety.
“Most companies are looking for LiFePO₄ batteries because it is a safe technology. And, as a supplier to the market, if we’re offering these batteries then they’ve got to have the protection there so that the battery can do what it’s meant to do,” Mr Skaines said.
“With MPS (Mictronix Power Systems), for instance, the BMS is designed specifically for their batteries.
“The owner of MPS actually comes from the solar industry so he knows the unique features of the inverters and how to protect his batteries from those elements.”
MPS batteries include two stages of protection: passive balancing and MOSFETs. To maintain the lifespan of cells and avoid over-charging and over-discharging, LiFePO₄ batteries need to be balanced before they come into service.
Mr Skaines said that balancing is often performed on site as part of the commissioning of a battery system, which can take one or two days to complete.
“MPS batteries are balanced before they get to market. That’s done in-house to make sure that they’re already ready to go in the field, and he also puts a flash test over the batteries to make sure there’s no hot joints or other potential issues in the battery,” Mr Skaines said.
MOSFETs act as the second line of defence by responding to signals from the BMS and electronically disconnecting the batteries when the temperature, current or voltage are outside the acceptable range.
“Some inverters will have voltage overshoot issues and MPS understands that, so [the owner] puts more MOSFETs in to protect the battery and make sure that we get a long, sustainable life out of it,” Mr Skaines said.
Although its strong tolerance to extreme temperatures and hazardous events makes LiFePO₄ one of the safest chemistries on the market, good chemistry alone does not guarantee complete safety.
“It’s really important that you do your research for your specific needs and ask questions of your supplier,” Mr Skaines said.
“On the outside, the batteries can all look flash but it’s what’s inside that’s important. Have a look at the warranty and ask questions about the BMS – they’re the parts of the battery that are going to protect you.”
Featured image: LiFePO₄ batteries are one of the safest chemistries on the market. Image: petovarga/shutterstock.com.
