Why Do We Use LiFePO4?

The tl;dr

Lithium Iron Phosphate (LiFePO4) batteries are the cheapest, safest lithium chemistry with lighter battery packs, long cycle life, and a maximum output profile, allowing for 90% usable capacity and many years of use. Hams love them!

I Need Power

Ham radio is a hobby that starts simply enough, normally through the purchase of a VHF/UHF handheld transceiver with its own battery pack and charger. Once an amateur radio operator decides that they want to go to more advanced HF and get their General class license (or move to mobile VHF/UHF rigs), that’s where the gear starts getting a little more complicated.

One of the things a new General class ham will find about new HF radios is there’s very little in the way of explaining how to power the more advanced rig. All you get is a funky Molex connector and a pair of bare wires with fuses on them. When I got my first HF rig, a Yaesu FT-857D, I was perplexed that I couldn’t just plug it in to the wall AC outlet.

Many manufacturers do this because they do not know how you will install your new radio. Mobile ones like the 857D I had are intended to be wired to the 12V electrical system of a vehicle. Larger desktop HF radios also use 12V, but the manufacturer does not assume how you’re supplying that 12V or what type of power connector you’ll be using, so they just give you a long pair of black and red wires.

Naturally, a new ham will want to either buy a 12V battery, or a 12V power supply. And not knowing any better, what are the 12V batteries we find everywhere? Car batteries. Sealed lead-acid (SLA) heavy batteries that power everything from motorcycles to boats.

What is a LiFePO4 Battery?

Lithium Iron Phosphate (LiFePO4) batteries are a type of Lithium-ion battery that use lithium iron phosphate as the cathode material instead of lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum (NCA), or lithium polymer (LiPo) electrolyte. All lithium-ion batteries are lighter, smaller, and provide more power than an equivalent capacity battery of older chemistry such as SLA.

Among the lithium batteries, it costs less to produce LiFePO4 than other types of lithium-ion chemistries. Iron and phosphates are common elements to find in the Earth’s crust, and have lower toxicity than electrolyte, cobalt, or nickel based chemistries. Moreover, LiFePO4 also does not experience thermal runaway at high temperatures like oxide and electrolyte lithium chemistries do (i.e. LiFePO4 doesn’t vent excessive oxygen to feed a fire and explode at above 150 degrees Celsius), hence LiFePO4 has a reputation as “the safest lithium-ion battery chemistry”. So what can cause a battery to get above 150 degrees C (302 degrees Fahrenheit)? Other than heating one in an oven, a simple short circuit or cell puncture can easily produce this level of heat very quickly.

Another aspect of lithium iron phosphate batteries is they have a longer cycle life than other lithium chemistries. LiPo batteries, the type you find in your cell phone or in small devices, normally have 300 cycles before significantly degrading in performance. NMC lithium batteries, such as popular 18650 cells, can go for about 1000 to 2000 cycles max. LiFePO4 is known under ideal conditions to go to 10000 cycles, but is more commonly expected to do 3000 cycles before degrading to 80% of capacity. Even after that LiFePO4’s are still usable. If you think about it, that’s 8 years of daily battery cycles in typical conditions, and upwards of 20+ years if you treat the LiFePO4 battery well.

Because each cell has a nominal voltage of 3.2V, four of these cells could be put in series to very closely match the profile of a traditional SLA battery. But unlike SLA batteries which get damaged if you drain more than 50% of their capacity, LiFePO4 can deliver 90% of their rated capacity and have safety mechanisms to prevent cell damage.

LiFePO4 Enters the Ham Hive Mind

At a certain point in the late 20-teens, ham radio operators began discovering that portable ops did not require lugging a heavy car battery along. Some hams had already been using RC batteries for their needs, but these would typically provide 11V instead of 12V, and were more dangerous to charge and carry in the field. Right around 2018, I discovered my first lithium iron phosphate battery for QRP operation. It was a 3Ah tiny blue battery from Bioenno. By then many hams had caught on that you could have a lighter, more reliable type of 12V power in the field. LiFePO4 could be discharged till they turn themselves off, could keep their charge for long periods of time, and were smaller for the equivalent amount of amp-hours.

Almost all LiFePO4 batteries have smart balancing and protection technology built into them via a Battery Management System (BMS) board. This prevents over-current, overcharge, over-discharge, short-circuit, and in some cases excessive temperature which enhances the overall battery’s safety.

A growing number of hams found that they could even source the individual parts of a 12V LiFePO4 battery and build one to their own specifications. Early pioneers of this like OH8STN Julian, and K8MRD Mike shared their battery building experience in YouTube videos. Picking the cells, capacities, BMS specifications, current flow estimations, and safety accessories was a hobby in itself.

Naturally, many people do not want to work with soldering and spot-welding, so many manufacturers and resellers (especially Chinese companies, since they have somewhat of a monopoly on LiFePO4 cell production) offer ever-cheaper finished batteries of varying qualities. These are originally intended to be automotive batteries, so if you see anything marketed as “B-rated” cells, those are batteries that did not pass the automotive tests or are used/recycled.

Charging Profiles

LiFePO4 charges best at 14.6V, which translates to getting each cell to 3.65V in a 4S pack. Many Lithium Iron Phosphate batteries will not engage cell-balancing, which is the process of bringing each individual cell to 3.65V as close as possible, if charged below 14.6 volts. Granted, you will get more cycle life out of your battery if you charge it at 14.2V, but its BMS may never be engaged and you won’t get all its potential performance. LiFePO4 batteries like constant voltage/constant current charging, and cut themselves off when full (via the BMS).

Compare this to a SLA charger for typical 6-cell 12V batteries that has concepts of bulk charge, float charge (a.k.a. trickle charge), absorption charge and equalization charge, all these different profiles that vary voltage and current from 13.8V to 14.7V. Can one use a SLA charger on a LiFePO4? Yes, but it is not good for it. These different charging profiles don’t agree with LiFePO4 batteries and will either not charge it to its potential or degrade it over time. SLA batteries like to be charged up constantly, especially when not in use. LiFePO4 likes to be charged then left alone. LiFePO4 has a very small self-discharge rate and can be stored for months, even years, and still work great.

Beyond 12 Volts

The 12V LiFePO4 battery market is just the tip of the iceberg. Many different industries are looking into safe, reliable, long-term energy storage in higher voltages. In the early 2020’s we have seen increasing numbers of rack-mounted 24V, 36V, and 48V systems in the tens of kilowatt-hour range that are intended use in off-grid/backup power systems, boats, and RV’s. Other products include higher voltage battery packs for use in EV bikes, and EV cars, uninterruptible power supplies, and emergency response mobile power trailers.

Even if you are not installing a whole-home backup power wall, many portable solutions are popping up. With the increasing regularity of natural disasters, I have received many inquiries about what is the best portable backup for a power outage during a storm or California fire. I recommend products such as Jackery, EcoFlow, Bluetti, EG4 for all-in-one portable power, as well as, of course, building your own setup with prismatic LiFePO4 cells, solar panels, and inverters.

So if you’ve ever wondered what LiFePO4 is about, why is it different from LiPo, and why not just get a cheaper SLA battery, hopefully this article has given you some insight into this modern battery chemistry.