Noel's Muses

It's time to consider alternatives that last for longer, and I mean much longer, these exist in the form of Lithium batteries which have many advantages over Lead Acid styles, such as less than half the weight with substantial increase of available power, both in longevity, and in sustained voltage output level, I've been running a couple for two years now and about to convert another UPS.

Most well known UPS manufacturers have for a number of years now offered Lithium batteries in more high-end equipment for Data Centre's, but in more recent times, they are starting to release consumer grade models as well, although the uptake due to their higher price tags is driving some to stick with the regular SLA models.

I can understand why some of you might be getting a little unsettled at the thought of yet another bigger Lithium battery in your house or office given all the media coverage of houses burning to the ground because eScooters and eBikes and electric vehicles going nuclear in the domino effect and sinking ships, there is a little truth to the dangers in some cases, but before you discard the idea - be informed.

There are several different types of Lithium chemistry, and the headline grabbing sensationalist media do what headline grabbing sensationalist media do, sensationalise and fear monger by withholding facts, because, headlines, ratings, you know... Tarring all Lithium batteries as one is wrong, scientifically wrong. After reading this article I hope you'll understand there are very safe Lithium batteries available, yet, there does still exist some dangerous types.

Safety of Lithium Batteries

Lithium refers to a family of Lithium based battery chemistries such as

• LCO: Lithium Cobalt Oxide
  
• LMO: Nickel Manganese Oxide
  
• NCA: Nickel Cobalt Aluminium
  
• NMC: Nickel Manganese Cobalt
  
• LiFePO4 (aka LFP): Lithium Iron Phosphate
  
• LTO: Lithium Titanate Oxide
  

Often, we hear that a product uses Lithium batteries, but this does not have any useful meaning of the chemistry used, it is fair to say batteries mostly commonly referred to as Lithium are Lithium-Ion NMC chemistry, but could also be older even more dangerous chemistries such as NCA, LCO or LMO. Each of these chemistries have very different characteristics, particularly with safety, then there's newer, better, safer chemistry like LFP.

Thermal Runaway

One of the main dangers of Lithium-Ion cells is the phenomenon of thermal runaway.

Thermal runaway is a heat-rise reaction due to the chemistry involved, it mainly occurs under specific conditions, such as overcharging, over discharging, charging below 0°C, all of which should be prevented by the BMS (battery management system) and of course, mistreatment, especially physical damage.

The extent of thermal runaway depends on the chemistry and a cells state of charge, in worst case scenarios, fire and often explosions of the Lithium-Ion cells which can have devastating affects to property and risks to life. When handled properly, and used with devices that include protection circuitry, and compliant chargers that also monitor and regulate voltages and current, these are usually perfectly safe, the high numbers of 18650 batteries out there in power tools, laptops, torches, and other devices since the 90's prove this.

The risks usually come from cheap imports of devices with inbuilt charging capabilities and or cheap no-name power supplies, neither having the required protection circuitry so can not regulate the charge and cut off when outside the safe limits so they just keep charging - likely the reason for many, if not all eScooter type fires, for example, you never want to charge a Lithium Ion cell which has a nominal voltage of 3.7v higher than 4.25v, nor let it get under 2.8v (LFP, as we'll discuss later, has a nominal voltage of 3.2v with a range of 2.5v to 3.65v), the protection circuit in most devices will cut out if the battery goes out of a safe range. The batteries BMS's use active balancing to detect and correct any minor differences in individual cells voltages, a battery is actually two or more cells and in UPS's with a nominal 12v, we have four cells, ok... starting to get a little outside the intended scope of the article now so let's get back on track before I lose you entirely

However, not all types of Lithium batteries, due to their chemical compositions, have the same sensitivity to this going nuclear thermal runaway phenomenon, the figure below shows the energy produced during an artificially induced thermal runaway


You can see that among the Lithium-Ion chemistries mentioned, LCO and NCA are the most dangerous from a thermal runaway point of view with a temperature rise of about 470°C per minute.

The NMC chemistry emits about half the energy, but with an increase of 210°C (250°C for LMO) per minute, this level of energy causes in all cases, internal combustion and the ignition of the cells and thermal runaway. This is most common on those pesky eBikes, eScooters, and EV's that are the cause of many fires.

Importantly, you can also see that LiFePO4 (also referred to as LFP or lithium ferrophosphate) is only slightly subject to the thermal runaway phenomena, with a temperature rise of a mere 1.5°C per minute.

With this very low level of energy release, the thermal runaway of the Lithium-Iron Phosphate chemistry is intrinsically impossible under most conditions, and even almost impossible to trigger with abuse, making it the safest Lithium battery chemistry available, even if the cells are violently abused, punctured and vent, the damage is controllable, and with a BMS the LiFePO4 cells are without a doubt the most stable and safest Lithium battery chemistry in existence.

Safety of Lithium Cells

Lithium cells have a different level of safety depending on the treatments they may endure during their lifetime. The nail penetration test is the most revealing way to ascertain the safety of a cells chemistry.

Tests perforating Lithium-Ion NMC cells and Lithium Iron LiFePO4 cells found extremely stable and safe behaviour with the LiFePO4 cells as we mentioned earlier, while the NMC cells ignited almost immediately, going off like firecrackers.

Additionally, LCO, LMO, NCA and Lithium-Ion Polymer or Li-Po (not to be confused with LiFePO4) (common chemistry in older “Pouch”) cells, all behave similar to NMC cells when perforated - immediate ignition, these cells also generate their own Oxygen, which is why submersion, smothering, regular fire extinguishing methods are ineffective to extinguish thermal runaway fires.

Don't be complacent! There are still dangers with any battery, even with LiFePO4, these next few points apply to all battery chemistries, the first is venting, what often looks like smoke is actually the release of leaked electrolytes, so what you are seeing is likely gases, dangerous gases that are very harmful, but at least with LiFePO4, it wont turn into a New Years Eve fireworks display.

Secondly, all batteries can be at risk from fire by heat generated by whatever is connected to the battery terminals, in fact this actually applies to everything electrical, AC and DC, so batteries and The Grid, cabling and connections - everything, and typically, that's loose connections, these cause high resistance, which causes heat, heat that can reach temperatures hot enough to melt a cables insulation and result in fire if laid on or near anything that is in any way flammable or if they short circuit, especially if you're using figure 8 cable and the positive and negative come into contact because all the insulation around them has melted away - you are well fused aren't you? Good, but that's not going to stop all ignition situations, manufacturers put torque settings on things for a reason! Be tight, but not over tight.

Alternatives to LiFePO4?

Lithium Titanate (Li2TiO3) aka LTO, is an emerging safe chemistry as well, however has drawbacks, the cost is high, about 2.5 times that of LiFePO4, its power density of 50-80Wh/kg is substantially less than LiFePO4's 90-120+Wh/kg, and its lower nominal 2.4v per cell is also sub par to LiFePO4's nominal 3.2v, compared to Lead Acid batteries with an energy spec of about 40Wh/Kg, so LiFePO4 batteries are less than half the weight with substantial increase of energy.

Can't You Be Consistent?

OK, so you're wondering why I refer to Lithium Ion and Lithium Iron – am I forgetful? being lazy?

Neither. Well not in this case at least as they are technically two different beasts.

Lithium Ion batteries are Manganese and Cobalt types, where as Lithium Iron is ferrophosphate, you know that Fe element for Iron on the periodic table in LiFePO4, the most used, plentiful and cheapest metal on the planet, might kind of give that away

Cost Benefits

The cost benefits of LiFePO4 over inferior chemistry like Lead Acid speaks for itself, how many SLA's (sealed lead acid) do think you'll be buying over 15-25 years for your UPS? I'm replacing mine about every 2 years for failure, I had one give up after only 18 months, my LiFePO4's cost me 80AUD each (iTechworld), the SLA's cost me about 40AUD each, in 4 years I'll break even, in 10 years, the LiFePO4's will still be cruising along, where I'd be on my fourth or fifth SLA batch (batch- because I've more than one UPS) and out of pocket an extra couple hundred dollars.

Depth of Discharge

Another big advantage is the fact that a LiFePO4 battery can without harm to the cells use 100% of its capacity, taken down to 0% without any damage, although doing so means you might only get 2000-5000 cycles before you start to lose efficiency of the cells down to 80% of its brand new state, in other words, it'll still be decades before the battery is actually kaput.

When buying the smaller UPS sized LiFePO4 batteries, they typically use 4 by 32700 or 4 by 32650 cylindrical cells (depends on capacity), the number of cycles in these will be closer to 2000 before losing efficiency, where the larger prismatic cells will yield double that easily before any degradation starts. You can prolong their life even more by using only up to 70 to 80% DoD (depth of discharge) of the batteries capacity without any degradation. Lead Acid batteries can only use 50% of their capacity else damage starts to occur dramatically reducing its life span, that's half the battery capacity unusable, resulting in LiFePO4 giving practically twice the runtime on one battery that's less than half the weight even when they both are rated the same Amperage.

What's in a Cycle?

It's also important to note that when a LiFePO4 battery spec quotes cycles, that's full capacity usage, it's easiest to explain if I give you an example, first the power sum, P=I*V (Watts=Amps*Volts) a 100Ah battery at a nominal 12.8v results in 1280Wh (Watt hours) capacity, so 1280Wh must be taken out of the battery for it to count as one cycle, it does not have to be in one hit, it can be gradual and even topped up in between, so if you have 1280Wh battery for let's say a remote CCTV camera and it uses 144Wh in 24 hours, and your solar tops it back up to a full state of charge every morning, that's going to take 8 and a half days of usage to count as one cycle, so this battery has the potential to provide full capacity in this role for many decades before it drops to 80% of its new capacity, thus providing 1024Wh for many more years.

So back to our UPS batteries, where (hopefully) it's rare they run at all, let alone to depletion, 12.8v * 7Ah gives us 89W to be drawn out for one cycle, might seem easy to drain given above example, but here in my office, consumption is about 63W, that's ample time to finish what I'm doing without rushing and let apcupsd shut down at low battery stage (I set that at what the UPS calculates to be 10min runtime remaining), and again it's rare we lose The Grid, so I should still see 20 years of use on this battery before it needs to be replaced, my home broadband router has its own UPS too, at 7W, the runtime is over 11 hours, and the longest time we've ever been without The Grid was 6 hours once, usually closer to 2H if a storm (or possum) takes out a transformer, the battery I expect will outlast me, the UPS with three servers, freepbx thinkcentre micro PC, a couple rpi's and switch is a different story, its runtime is only a mere 42mins, but then there's a generator for that

Voltages

There's one more advantage of Lithium, Lead Acid batteries have a constant discharge drop curve, the voltage gets less and less as the battery is used, Lithium cells drop a little bit once full charging ceases at 14.6v down to 13.5v to 13.8v and there it mostly sits providing a stable constant average of 13v until the battery is almost at depletion (80-90%) where it will then quickly decline to about 10.5v and the BMS would disconnect the batteries, this makes them perfect for critical functions, especially in things like emergency lighting systems.

Concluding

Word of warning, Victron Energy, a popular, yet rather over priced supplier of Solar regulators, controllers and other related components, have been selling LFP batteries without a BMS, these batteries as of October 2023 are illegal to sell or install in Australia, as all Lithium batteries are required by legislation to have a BMS. Victron like to make you pay for features, and this is one of them, iTechworld in Perth manufacture and supply LiFePO4 batteries, as does another international, Renogy, who also supply regulators and other Solar equipment, both of these are reasonable priced, iTechworld I'd recommend for UPS batteries, but for high capacity 100/200/300Ah batteries, I'd recommend Renogy's.

Other words of caution for drop-in LiFePO4 replacements into UPS's designed for SLA's, just remember that some of these UPS models are designed to calculate run time for SLA, meaning it might put you into LowBatt state when you still have 20 minutes left, not all UPS's are equal, and although 12v LiFePO4 batteries should be charged to 14.6v, most SLA UPS's will only charge to 14.4v, this is still safe and most workable, you'll still get better performance and life out of the cells, every twelve months though I pull mine out and throw them on the bench and use CC of .2c (constant charge current of 20% of the battery Amperage rating) at 14.6v for that extra little top up, it usually ends 10 minutes later, so not sure if it's really worth the effort anyway.

This write-up is primarily for UPS batteries, but the same information applies be it a 7Ah UPS battery, or a 300Ah you're chasing to stick in a camper, RV, or boat. BTW If chasing the larger capacity batteries, ensure the cells are prismatic, you get even better sense of protection from them that you can't get in pouch style or 32700 cells LFP's in small batteries like for UPS's.


Always exercise caution when working with batteries, gloves and eye protection are a must, beware sparking, this can be normal when connecting the batteries to the UPS, but might alarm someone the first time it occurs.

Always handle a bulging battery with extreme caution, especially with older UPS batteries, if you experience difficulty removing the old battery, and it is bulging, do not ever use tools to force or pry it out, use gentle push-pulling to remove it, and take the old battery to an authorised disposal centre, Battery World will accept these and dispose of them for you at no charge.

The thermal runaway Image in this article is used under Fair Use terms and remains copyright of Sandia National Labs