Lithium iron phosphate (LiFePO4) batteries have a wide range of applications. They power electric vehicles and store solar energy for home use. You’ll also find these batteries in some consumer electronics, such as smartphones and laptops.
An LFP battery contains Lithium salt as an electrolyte. The most commonly used Lithium salt is Lithium hexafluorophosphate (LiPF6). Some batteries use Lithium tetrafluoroborate (LiBF4) as an electrolyte.
Usually, the battery charge reduces if you connect a device that draws electrons from the cathode terminal. You want to avoid deep discharge to prevent battery damage. We’ll explore LiFePO4 Batteries in more detail.
Characteristics of LiFePO4 Batteries
LiFePO4 also called LFP batteries, are a type of Lithium-ion batteries used in many electric vehicles and electronics. While all Lithium-ion batteries use graphite material for the anode, they use different materials for the cathode. LFP batteries specifically use lithium iron phosphate for the cathode terminal.
Lithium Iron Phosphate Chemistry
During the discharge process, the LFP battery provides electrical power. Chemical reactions in the battery cause Lithium ions to move from the anode (the negative terminal) to the cathode through the electrolyte.
Lithium ion deficiency in the anode results in electrons flowing from the anode to the cathode through a circuit. This electron flow generates electrical energy that powers devices connected to the LFP battery.
If the electrical power output reduces, you’ll charge the battery to boost its energy reserve. Lithium ions move back to the anode from the cathode through the electrolyte during the charging process. More ions on the anode cause a push of electrons from an external circuit to the cathode. More electrons pushed into the cathode means more energy to power connected devices during discharge.
LiFePO4 Battery Vs. Other Lithium Ion Batteries
LFP batteries are compared with other lithium-ion batteries in two main areas:
Cycle Life
LiFePO4 batteries can handle more charge-discharge cycles before losing a significant charge capacity. If you want a battery that will provide reliable electrical power longer than other Lithium-ion batteries, an LFP battery is the best option.
Energy Density
Even though LFP batteries boast a longer cycle life, they don’t hold as much energy as other Lithium-ion batteries. Other types of batteries like Lithium Cobalt Oxide (LiCoO2) and Lithium Nickel Manganese Cobalt Oxide (NMC) hold more Watt-hour of energy per kilogram or liter.
For example, Lithium Cobalt Oxide batteries hold 150-200 Wh of energy per kilogram while LiFePO4 holds 90-160 Wh of energy per kilogram. At the same time, LiNiMnCoO2 or NMC batteries hold a staggering 200-300 Wh of energy per kilogram.
Advantages of LiFePO4 Batteries
LFP batteries outperform other Lithium-ion batteries in other areas. In addition to boasting a longer cycle life, LFP batteries have these advantages:
Thermal Stability
LiFePO4 batteries can reliably provide electrical power under high temperatures. What’s more, LFP batteries don’t generate as much heat as other Lithium-ion batteries during self-sustaining reactions.
Fast-Charging Performance
Better thermal stability allows an LFP battery to take in more electrons from an external circuit per minute. What’s incredible is that an LFP battery doesn’t degrade while taking in more electrons.
Excellent Safety Record
Since LiFePO4 batteries don’t generate more heat during the charging and discharging processes, they are less likely to overheat, catch fire, or explode.
Reliable Power Supply
An LFP battery consistently supplies volts to the connected device until the battery runs out completely. The voltage output doesn’t reduce as the battery charge plummets, guaranteeing reliable performance throughout the discharge period.
Typical Applications of LiFePO4 Batteries
LiFePO4 batteries are used to power electric vehicles, store renewable energy from the sun, and power electronics like smartphones and power banks.
- Electric Vehicles (EVs): Some electric vehicles rely on LiFePO4 batteries to power the electric motor. Moreover, the battery also powers the infotainment system, headlights, and climate controls.
- Renewable Energy Storage: Solar panels connected to LiFePO4 batteries add electrons to the cathode terminal, adding electric charge to the battery. When it’s dark outside, the electrons flow out of the cathode via an external circuit.
- Portable electronics: LFP batteries also power devices like laptops, tablets, and power banks. These batteries also power cordless tools like vacuum cleaners and power saws.
The Concept of Battery Drainage
Battery drainage is discharging the battery by connecting a device that draws electrical charge from the battery. Lithium ions move from the anode to the cathode through the electrolyte. The ions combine with the iron phosphate (FePO4) compound on the cathode, resulting in electrons flowing out of the cathode to the connected device.
Types of Battery Drainage
Drawing electrons from the battery drains the charge. Devices connected to the battery can drain a LiFePO4 battery. However, a battery can also lose electrons by itself, causing self-discharge. There are different types of discharge:
Partial Discharge
Partial discharge happens when a portion of electrical charge (electrons) flows out of the battery, leaving some electric charge.
That means there will still be some charge left when recharging the LiFePO4 battery. Think of partial discharge as a battery used but not fully depleted. The battery might be 30% full before a recharge.
Deep Discharge
Deep discharge happens when you spend almost all the electrical charge stored in the battery. If you connect a device to a LiFePO4 battery and it consumes 95% of the electrical charge, you’ve exposed the battery to a deep discharge.
This type of discharge is to be avoided because it reduces the battery charge capacity. It also pushes the battery chemistry to its limit resulting in reduced battery lifespan.
Self-Discharge
All batteries lose charge on their own, even when not in use. The chemical reactions in the batteries result in electron loss. Storing the battery under high temperatures can speed up the chemical reactions and increase the rate of self-discharge.
Comparison to Other Battery Types In Terms of Drainage
LiFePO4 batteries have a slower self-discharge rate than other types of batteries. An LFP battery can retain more electrical charge when not in use, making it the best for storing electrical energy.
While many Lithium-ion batteries maintain excellent performance through thousands of charge cycles on partial discharge, some, like the Lithium Cobalt Oxide(LiCoO2), degrade faster. LiFePO4 batteries perform better and last longer on partial discharge.
We wouldn’t recommend a deep discharge because it damages the battery. However, LiFePO4 batteries tolerate deep discharge better and will last longer.
Effects of Draining LiFePO4 Batteries
Draining an LFP battery (or any lithium-ion battery) affects the battery lifespan and charge capacity.
Impact on Battery Lifespan
Depth of Discharge (DoD) is the percentage of the charge used so far. For example, a battery that’s 80% used has a depth of discharge of 80%. DoD has an impact on the cycle life or charge cycle. A partial discharge of 30% - 50% can lead to charging a LiFePO4 battery thousands of times before a performance degradation.
On the other hand, a deep discharge of 80%—100% depletes the charge cycle quickly, meaning the battery will degrade much faster. Keep your LFP battery on partial discharge to prolong its lifespan.
If you’ve depleted the charge in a LiFePO4 battery, you can recover the battery performance through careful handling of the battery. Before recharging the battery, check that each cell provides 2.5 Volts. You’ll also use a low-current charger to boost the electrical charge.
Ensure your low-current charger applies gradually increasing volts to the battery until each cell has a volt output of 3.0 V. You’ll then switch to a normal battery charger to boost energy to full capacity.
Performance Implications
Draining the battery depletes active materials in the LiFePO4 battery. As a result, the battery has a reduced ability to generate electrical potential. A deep discharge reduces voltage output in any Lithium-ion battery.
What’s more, draining the battery reduces the capacity of the battery to hold more electrical charge. If you deeply discharge a battery, some Lithium ions are trapped in the battery’s internal structures. These ions are “dead Lithium ions” because they don’t travel through the electrolyte to participate in the charge-discharge cycles, leading to the battery holding less electrical charge.
At the same time, draining your battery increases internal resistance within the battery. Deeply discharging a battery causes chemical changes in the electrolyte. The electrolyte then hinders ions' movement between the terminals, resulting in electrical resistance inside the battery.
Recommendations for Battery Management
Battery management is a practice that keeps the battery working optimally throughout its lifespan. One of the ways to maintain a battery’s optimal performance is by discharging it safely.
Ideal Discharge Practices for LiFePO4 Batteries
Partial discharge of 30% - 50% is an ideal practice because it maximizes the battery lifespan. You want to avoid deeply discharging your battery frequently because this practice leads to more dead Lithium ions, which reduce the electrical power output. You want to keep the depth of discharge (DoD) between 20% and 80% to maintain a stable state of charge.
Best Practices for Extending Battery Life
Aside from the partial discharge cycle, you want to avoid overcharging your battery. You can use a battery charger that automatically stops charging the battery at 100% capacity. Overcharging the battery can degrade the electrolyte and damage electrical conductivity.
It’s also important to keep the battery under favorable temperatures. Keep the battery away from direct sunlight or heat sources. Extreme temperatures like freezing or high temperatures accelerate electrolyte degradation.
When using your battery, ensure you don’t deplete its charge below 80%. You want to recharge the battery at a depth of discharge of 80% to avoid exhausting its charge cycles fast.
Since lithium ions can shorten their lifespan, you want to prevent their formation. Charging and discharging the battery periodically reduces the chances of dead ions formation. If you intend to store your battery for later use, first, ensure it’s in a cool and dry storage compartment.
Second, ensure it’s partially charged. Storing the battery at a 50% charge prevents the deep discharge it would experience if you stored it at a 100% charge capacity.
The Bottomline
LiFePO4 battery reigns supreme over other Lithium-ion batteries. It can withstand extreme temperatures better and takes in more electrons to charge faster. What’s more, LFP batteries have a longer lifespan. However, they don’t hold as much energy per volume or mass as other Lithium-ion batteries.
But they are a great power source for portable electronics like smartphones and power tools. You can get the most out of them, especially if you avoid draining the battery before a recharge.
