The difference between lithium iron and lithium-ion, and why it matters

Lithium iron phosphate batteries are part of a group of batteries called lithium-ion batteries. Specifying that a battery is a lithium iron, or lithium iron phosphate, battery implies a host of characteristics which are important when choosing a battery type and provider, says REVOV co-founder and engineering director, Felix von Bormann.

Lithium iron phosphate batteries (LiFePO4, or as some refer to it, LFP) have many advantages, says Von Bormann. “Lithium Iron Phosphate batteries have a great energy density and lifecycle, a stable chemistry all while maintaining high thermal runaway and resulting in a long life at low costs.”

Lithium-ion batteries are secondary cells created from layers of lithium packed with an electrolyte. A lithium battery is formed by four important components namely the cathode, anode, electrolyte, and separator.

The cathode, a positive electrode, determines the capacity and voltage of the battery and is the source of lithium ions. The anode, a negative electrode, stores the lithium ions when the battery is charged and enables the electric current to flow through an external circuit. The electrolyte is formed of salts, solvents, and additives and serves as the channel of lithium ions between the cathode and anode while the separator is the physical barrier that keeps the cathode and anode apart.

The cathode is a metal oxide, and the anode consists of porous carbon thus during discharge the ions flow from the anode to the cathode through the electrolyte and the separator, when charging the battery, the reverse happens the ions flow from the cathode to the anode.

Lithium-ion batteries come in many varieties, although remarkably similar on the surface these batteries vary in performance and the selection of active materials gives them distinctive qualities. There are six main versions of Lithium-ion batteries namely Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Iron Phosphate, Lithium Nickel Cobalt Aluminium Oxide and Lithium Titanate.

The cathode is what differentiates each battery. For example, the Lithium Cobalt Dioxide is made with a LiCoO2 cathode while the Lithium Iron Phosphate battery is made with LiFePO4 as the cathode. This means that there is a technical difference between Lithium-ion and speaking about Lithium Iron. Lithium-ion references the mode of electrical transfer inside the battery, where ions travelling in the electrolyte are lithium. Lithium Iron is a subset of the family of Lithium-ion batteries.

Despite the characteristics they have in common, the different Lithium-ion systems and Lithium Iron batteries are different in terms of their stability, life span and application. Lithium Iron Phosphate has a high current rating and long cycle life, it is more tolerant to full charge conditions and is less stressed than other lithium-ion systems. It has a specific energy of 90/120 watt-hours per kilogram, a nominal voltage of 3.20V/3.30Va, a charge rate of 1C, and a discharge rate of 1-2,5C.

Von Bormann says Lithium Iron Phosphate loses some distance in terms of specific energy per kilogramme, “However, this is not important in a stationary application where weight is less important. The Lithium Iron Phosphate cell is superior in terms of safety and price, over other Lithium-ion battery chemistry, and typically has a higher life expectancy and a higher specific power,” he says.

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Plugging into the reality of 2nd LiFe batteries: second life is not second-hand

“A 2nd LiFe Battery is not second-hand. A 2nd LiFe battery has been repurposed and the cells have had their life extended by being applied to less strenuous operating conditions.”

A pioneer in the sector, REVOV, has been developing and supplying 2nd LiFe storage battery systems in South Africa and neighbouring countries for four and a half years. Not only is an investment in second life technology the environmentally prudent thing to do, but it makes sense from a performance and price perspective and international players have discovered this.

After a few years electric (EV) batteries are replaced with new ones because the weight of the battery in the car no longer justifies its performance. However, when the cells are repurposed for storage batteries, there is a compelling solution to preventing huge numbers of batteries being dumped into landfills.

The concept and application is gaining traction around the globe, and bolster’s REVOV’s resolve. The Australian Renewable Energy Agency (ARENA) said Relectrify, which has been working with American Electric Power and Nissan North America on a pilot project, will now finalise development and undertake certifications ahead of the deployment of 20 ReVolve battery units across C&I applications throughout Australia.

In order to understand what it is that REVOV and its international counterparts are seeing in 2nd LiFe, we delve a little deeper to understand the science behind these batteries particularly now that load shedding is once again on every South African’s agenda.

We asked REVOV MD Lance Dickerson to plug us into the reality of 2nd LiFE batteries and what they are:

Please go into a little detail of why automotive grade batteries are so transferable to storage?

Automotive grade cells are manufactured specifically for use in the very harsh environment of a motor vehicle. This includes being mobile, subjected to vibrations continuously, high temperatures and to high charge and discharge currents in the effort to optimise charge time vs distance vs speed.

Stationary storage applications change this high throughput requirement, and optimise the requirement to provide a lower throughput over a longer period of time, significantly enhancing the life expectancy of the once automotive battery.

In which circumstances in daily use will this come in handy, or will the owner notice these benefits?

Typically a backup storage battery is dimensioned to provide power throughout the night, around 10 hours or more, or at worst for at least the four hours of load shedding we all have come to love.  The battery, dimensioned to provide 10 hours of backup, is only typically running at 1/10th of its maximum output which lends itself to an extended life, and an optimal cost per kWh.

Effectively, an automotive grade cell running at less than 1/10th of its design potential can obviously be expected to last longer than originally planned

Let’s compare 2nd LiFe Lithium-iron to other types of batteries. What are you prepared to say, if anything?

Firstly, Any Lithium Iron Phosphate cell is superior in terms of safety, over any other Lithium Ion battery chemistry, and typically has a higher life expectancy and a higher specific power. It loses some distance in terms of specific energy per kg, however, this is not important in a stationary application where weight is less important.

Secondly, an automotive grade 2nd LiFe Lithium Iron Phosphate battery, used in a stationary storage application, is subjected to charge and discharge currents that are significantly lower than its design capability. This reduced stress translates into a non-linear improvement in terms of cycle life, easily providing the same lifespan as a new battery specifically designed to provide stationary storage only, at a much-reduced cost.

When we say a battery is repurposed (2nd LiFe). What does this specifically mean?

A 2nd LiFe battery can take on a number of different shapes and sizes. If the battery is removed from the vehicle and found to be in exceptional condition it can be used as is, in a mostly 12v configuration, at medium-to-low charge and discharge rates. The only addition would be an external battery management system which would ensure the battery cells are protected from excessive charge and discharge currents and voltages and ensure the cells inside the battery remain balanced.

Most often the capacities and voltage combinations used in modern EVs are not suitable for the modern 48VDC renewable energy system. Most 2nd LiFe battery cells are unpacked from the vehicle battery casings and packed into formats that suit their usage in the environments they are being destined to. This requires new components in every part of the battery except the battery cell itself.

As an example, a very popular format is the 19-inch rack-mountable size, allowing them to be mounted easily in cheap IT-type cabinets. 2nd LiFe can be packaged into almost any shape, size, capacity and for any application, you can imagine. Easily packaged into tubular shapes for mounting around poles at height, into thin wide arrangements to fit behind 4×4 seats for auxiliary power whilst camping, into small cubes to fit into UPSs created for rectangular Lead Acid batteries, and almost any other use you can think of.

In your words, what is the difference between 2nd LiFe and second hand (if there is more to it than above)?

A 2nd LiFe battery has been used in a motor vehicle, or mobile application specifically as a primary source of power to drive the vehicle. Its 2nd LiFe is engaged when the battery has lost approximately 20% of its original capacity, and due to weight being an issue in a mobile application, its purpose is changed to become mostly a secondary power source, storing energy generated by renewable sources or Eskom Grid power. This energy is stored and then used at a reasonably mediocre rate to provide power when renewables such as wind and sun are not available or to provide backup power for periods longer than two hours.

This process effectively extends the life of the battery giving it what we term a 2nd LiFe.

In contrast, a second-hand battery would be a storage battery used to provide storage for a time, uninstalled and re-installed to perform the same function in another location. Nothing in this process extends its life or changes the conditions under which it operates and it will simply last as long as originally planned.

What is the lifespan of 2nd LiFe in cycles and years?

Due to the reduced stress, and the history provided with a 2nd LiFe battery, by the vehicle BMS, lifespan is easily predicted forward.

Most 2nd LiFe batteries were originally designed with a life expectancy of 6 000 to 7 000 cycles in an automotive primary power source application and applied into 2nd LiFe applications once they have endured 1 500 to 2 000 cycles in a vehicle.

This means they still have a life expectancy of another 4 to 5 000 cycles under the same conditions as in the vehicle. But stationary storage reduces the stresses on the battery cells enormously from their design capability and hence the life span of the 5 to 6000 additional cycles is easily met.

In REVOV batteries – which components are brand new in the 2nd LiFe batteries – electronics, cases, display etc?

The only component inside a REVOV battery which is not new is the actual battery cell. From the busbars interconnecting cells, to the monitoring harnesses, cables, and sensors, casing, connectors, screws, and bolts, all are new. The Battery Management System used is specifically designed for the 2nd LiFe cells and is not the same system used in the vehicle either.

What are some of the biggest REVOV 2nd LiFe installations you are aware of, and were they used for UPS or renewable setups?

We currently have a number of REVOV 2nd LiFe installations exceeding 320kWh, these are in total off-grid applications where the customer has disconnected Eskom or doesn’t have reliable access to Eskom, to similar size units which provide UPS functionality in case of Eskom failure. These are typically in the 48V nominal range, and 300-350 kWh is really the limit that a low voltage (48VDC) installation should be built at. Larger than that the requirement for larger conductors becomes critical, and installation becomes impractical.

The vast majority of our installations and applications are between 10kWh and 100kwh. We are currently working on some much larger applications, but these will ultimately use a High Voltage setup and design, where the batteries are connected in series to reach voltages up to the 800VDC range, this, in turn, has a significant effect in terms of ease of installation and cable sizes and costs.

Watch this space carefully as REVOV launches the first 2nd LiFe HVDC battery product in Africa in the next few months.

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