The One Critical Weakness of Lithium Batteries No One Warns You About
Lithium ion batteries have gained popularity in recent years, and rightly so. With applications ranging from tablets and smart phones to off-grid solar systems and electric cars, Lithium batteries have gained quite the reputation. Still, with all it’s popularity, I’ve been surprised lately by the lack of education when it comes to lithium ion maintenance, and the one critical aspect no one is talking about.
For off-grid solar applications Lithium ion batteries have many advantages:
- Does not degrade when stored at partial charge, as with lead-based batteries.
- Low self-discharge. Your battery bank can sit for long periods of time without needing to be charged.
- Low maintenance
- Long lasting with thousands of life cycles, as opposed to lead-based batteries with hundreds of life cycles.
- Lighter with higher energy density (more watt-hours per kilogram)
For off-grid solar, Lithium batteries are the most advantageous battery we have on the market right now. However, their biggest disadvantage is that they can be extremely dangerous if not managed properly. Which is kind of important small print that no one tells you about- which is why I’m writing this article.
Have you ever wondered why the top electric car manufacturers use an extensive system for maintaining battery temperature with their Lithium battery systems? Tesla and Chevy both use a liquid heating/cooling system integrated into their batteries to keep the temperature above 32 deg, and below 120 deg.
I’m here to tell you that they don’t do this just for fun. There is a good reason why Lithium batteries need to be maintained and charged within a specific temperature range, and I find it very disturbing when I see people claiming you can use lithiums at an extreme temperature range of -40 to 140 deg F. Lithium battery usage at temperatures up to 140 deg will significantly shorten their life span, and charging below freezing is extremely dangerous.
In other words, never charge lithium ion batteries in below freezing temperatures.
Doing so even once will result in severe and permanent capacity loss, and even worse, it causes damage to the battery that makes it unsafe to use and should be, safely recycled or otherwise discarded. When I say not safe, I mean it will work fine until it randomly explodes due to mechanical vibration, mechanical shock, or just reaching a high enough state of charge.
Lithium ion batteries are generally under a lot of internal pressure, unlike other battery chemistries. Lithium batteries store energy like two springs. During charging or discharging, lithium ions move through a separator, from one side to the other. As these ions move back and forth it causes stretching and contracting of the internal components which causes mechanical stress on the battery. It’s important to note that this is a completely normal process for Lithium batteries.
Another difference is their electrolyte is a volatile and extremely flammable solvent that will burn quite easily. There are a variety of different chemistries of lithium batteries, all with different levels of reactivity and inherent danger, but the ones with high energy density can undergo thermal runaway. Meaning, if they get too hot, the lithium ions will begin to release more heat, getting hotter until it catches fire or explodes, and there’s nothing you can do to stop it.
Now before you get too worried, the temperature for thermal runaway to start is around 300 to 500 deg F (depending on they type of battery). So this is unlikely to happen, unless there is damage to the internal components of the battery. Which leads us to the charging your batteries below freezing.
When you charge a lithium ion cell in below freezing temperatures, the lithium ions fail to bond in the anode correctly. Instead, they plate the anode with metallic lithium. This lithium platting of the anode isn’t smooth and even – it forms in dendrites, which are sharp tendrils of lithium metal growing on the anode.
The lithium coating damages the battery and reduces it’s capacity, but more importantly, the dendrites can put unexpected pressure on the separating membrane as the anode expands and forces them into it, and this will cause the membrane to one day fail unexpectedly. This of course makes the cell vent, and ignite its flammable electrolyte.
Note: I should add that discharging a lithium ion battery in below freezing temperatures is perfectly safe. Most cells have discharge temperature ratings of -20°C or even colder. Only charging a ‘frozen’ cell needs to be avoided. Also, if your battery has active heating then you can charge the battery in below freezing temperatures because the battery itselfwill not be below freezing.
So how do you avoid lighting up your battery bank like a bonfire? If you know you’ll be charging your batteries during freezing temperatures, make sure your battery bank has a temperature control feature that regulates the battery temperature, or keep it in a temperature controlled, insulated room like a heated garage or shop (like this photo of our HomeGrid solar generator hooked up to a 40Kwh lithium battery bank). If this isn’t possible, you’ll need to avoid using them during freezing temperatures, and save the bonfires for campouts.
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Why are lithium ion batteries being used in the titan instead of lithium iron phosphate? Isn’t the former more dangerous?
Just to be clear, lithium iron phosphate are also lithium batteries, they are just a different chemistry than what we use. We use an NMC battery, because its energy density is much higher (making the batteries much lighter and more portable). NMC batteries are also extremely safe in the way we use them with the Titan. We have many safety checks involved, and have never had a single issue with safety due to the battery. Just to give you an idea, our batteries are safe up to 419 degrees Fahrenheit (safe in that they won’t start on fire, but they will be damaged at lower temperatures), and our BMS will turn the battery off before they are damaged. Lithium iron phosphate can go up to 518 deg. So yes it is safer, but both are very safe if used correctly (with a Good BMS, like what is in the Titan).
Thanks Dave W.! I wonder if one of the cigarette ports with the car charger cable could be used? However, the DC-DC sounds like a better means to stay on the job and I could monitor the battery with my battery capacity meter? I’m going to look into the Victron…
Charging the 12V battery with the cigarette port could work, however it has a limit of 20A. So as long as you only used a little power as to never go over 20A charging, it should work. Also the battery would need to be very close to 13.8V when you connect it to the cigarette port or it would blow the fuse instantly. I think the victron DC-DC charger would be a much better more reliable solution. You would just connect that to one of the AC charging ports (I know that sounds funny, but those ports go directly to the battery except they go through the battery meter so it will stay accurate).
I want to run a Chinese diesel heater next winter and I want to run it on a 12 volt battery. Does any one know if I can use the external battery port on my TITAN to keep the battery charged and running this heater. Ron C
The Titan uses a 24V battery. So if you want to keep a 12V battery charged, you would need to use a DC-DC charger or an AC charger. The AC charger is much easier to find and cheaper, but is less efficient due to converting to ac, then back to dc. Victron energy makes good DC-DC chargers.
Incredibly useful info for off-gridders in freezing climates
you need to fix misprint in last paragraph, “40kw lithium battery bank”
You probably meant 40kwh
Fixed. Thank you.