How to take care of your lithium iron phosphate battery

Lithium iron phosphate (LiFePO4) batteries are becoming the most popular standard battery choice in many applications. Understanding the characteristics of lithium batteries can help maximize the batteries' life span, the safety of the battery, and the best performance for your application.

What is a Lithium Iron Phosphate Battery?

Lithium iron phosphate ( also known as LiFePO4 or LFP) batteries are becoming the most popular used battery chemistries today because of their lightweight structure, high energy density, long lifespan, long working time and safe. Lithium iron phosphate (LiFePO4) batteries are made up of multiple lithium cells with a circuit board that protects the cells.

The structure of lithium battery cells consists of anode, cathode, separator, electrolyte, and two electric current collectors (positive and negative). The lithium is stored in both the anode and cathode, while the positively charged lithium is carried from the anode to the cathode by the electrolytes and vice versa through the separator. The movement of charges will generate a charge on the electric current collector, which will deliver electricity through the anode and cathode to the battery's terminals. This generates a voltage potential that leads the current to flow from the positive terminal to your application, and then back to the negative terminal.

How Do l Maintain Lithium Batteries?

While rechargeable lithium iron phosphate (LifePO4) batteries have a long lifespan, but, they will also lose their ability to hold a charge over time. Once your batteries have lost their capacity, that is permanent. Therefore, it is significant and necessary to properly care for and maintain lithium batteries.

An estimated life expectancy of a lithium iron phosphate (LiFePO4) battery is 8 -10 years, this is depending on how users operate it. LiFePO4 batteries will provide up to 2000 complete charging cycles or as many as 5000 partial cycles at 80% DOD. A complete charging cycle is referring that you use of the battery from fully charged to completely discharged, and then fully recharged again. Your LiFePO4 batteries' lifespan may be hampered or damaged if you leave them unused for extended periods of time, which will ultimately result in a failed battery. if you left it too long.

We recommend all Enjoybot users that all unused LiFePO4 batteries and cells go through at minimum one full maintenance cycle (charge to 100% SOC (state of charge ), discharge to 100% DOD (depth of discharge), charge to 50% SOC) at least every 3 - 6 months to maintain the capacity of batteries. Users need to check their LiFePO4 batteries in storage for adequate OCV (open circuit voltage). Usually, the cells need to keep in the range of 3.3v -3.4v, and the 12V batteries should keep in the range of 13.4v-13.6v. If the voltage falls below this value during a maintenance check, we recommend re-charging the battery to the top of the voltage ranges as we listed below.

Voltage Range (v)                Lithium-iron Phosphate Product Type

3.3-3.4                                     Individual Cell

13.4-13.6                                 12-volt battery pack

26.4-27.2                                 24-volt battery pack

39.6-40.8                                36-volt battery pack

52.8-54.4                                 48-volt battery pack

When checking the voltage of the cells or batteries every 3-6 months, please inspect for terminal corrosion and case integrity. Do not use any battery that appears to be damaged.

The LiFePO4 battery will continue to slowly self-discharge while in storage or unused, regardless of how carefully you take for and maintain your batteries. If your batteries have a function of Bluetooth, the batteries' self-discharge rate will be higher due to the draw of the Bluetooth module. Regularly checking your batteries' charge periodically will continue to keep your batteries in better health and produce more energy for your application.

A good measure of health that is easy to do at home is to monitor the run-time of your application. When you are shopping for lithium batteries, note the run time the new batteries provide for your application (you will need to calculate the run time with Ohm's Law formula). This brand-new run time will be a baseline that can be compared as your battery ages to gauge its health of the battery. The run time of the LiFePO4 battery will vary depending on the application and configuration you are running.

How Do l Charge a Lithium-iron Phosphate Battery?

A lithium-specific battery charger is the best option for a LiFePO4 battery when it comes to charging and this ensures a full charging cycle each time. The LifePO4 battery charger features an intelligent three-step charging logic to help charge even the deepest discharged batteries. In addition, to maximize the LiFePO4 battery performance and its lifespan, the optimized charging technology makes the best possible use of the capacities of the batteries to be charged. But can I use a lead acid battery charger to charge a lithium battery? There are many similarities in the charging characteristics of SLA and lithium. However, extra caution should be exercised when you are using the SLA charger to charge lithium batteries as they can be damaged, undercharged, or reduced the capacity of the lithium battery over time.

The fully charged 0CV of a 12V SLA battery is nominally 13.1 voltages, whereas the fully charged 0CV of a 12V lithium battery is nominally 13.6 voltages. Batteries will only be damaged if the applied charging voltage is much higher than the full charge voltage of the battery.

SLA batteries should be kept below 14.7V for bulk charging, and lithium batteries should be kept below 15V. Float charging is only required for SLA batteries, so recommended around 13.8V. Based on this, any lithium or SLA battery can be charged safely with a charging voltage range between 13.8V and 14.7V. When selecting a charger for either chemical substance, it is essential to choose a charger that will remain between the limits listed above.

What Charging Rate Would Extend the Life Span of a Lithium Battery?

The charger is selected based on a small part of the capacity of the battery. For example, the lead acid battery might be kept below C/3 (one-third times the capacity of the battery), however, the lithium battery can be charged as fast as 1C (one time the capacity of the battery). This means that a 10Ah lithium battery can be charged at 10 amperes, while a 10Ah lead acid battery can only be charged at around 3 amps.

We advise charging LifePO4 batteries no slower than C/4 and no faster than C/2 in order to maximize lithium batteries' lifespan while balancing fast charging to reduce downtime. Let's go back to the 10Ah battery example, this would be a charging speed of 2.5A to 5.0A, with 2.5 being the best case. If you were looking at chargers and there is a 2A charger and a 5A charger, we would recommend you go for the 2A charger. Charging with a 5A charger will take about 2 hours, but it may shorten the battery's life. Charging with a 2A will take about 5 hours, but it will maximize the life of the battery. Thus it can be seen, The charge cut-off current is 2.5-5.0% of the capacity, and the cutoff for both batteries would be 0.25-0.50A. Typically, the current termination setting is determined by the charger and there is no need to worry about setting it properly to maximize the battery’s life.

Universal battery chargers will typically feature a function to select the chemistry which is an excellent way to extend the battery life. This function selects the optimal voltage charging range and determines when the battery is fully charged. For instance, if it charges a lithium battery, the charger should shut off automatically. It should switch to a float charge if it is set to charge an SLA battery.

Long Term Storage

If you need to store your batteries for an extended period, there are a few things you will have to consider as the storage requirements differ for SLA and lithium batteries.

First is that the battery's chemistry determines the optimal storage SOC. With SLA batteries, you want to store them as close as possible to 100% SOC to avoid sulfating, which leads to a buildup of sulfate crystals on the lead plates. The buildup of sulfate crystals will reduce the capacity of the battery.

For lithium iron phosphate (LiFePO4) batteries, the structure of the positive terminal will become unstable when depleted of electrons for long periods. The instability of the positive terminal may result in permanent capacity loss. This means lithium batteries should be stored as close as possible to 50% SOC, which equally distributes the electrons on the positive and negative terminals.

The second impact on storage is the batteries' self-discharge rate. The high self-discharge rate of SLA batteries means that it is best to keep them on a float or trickle charge to maintain it as near as possible to 100% SOC to avoid sulfation and permanent capacity loss. For lithium batteries, however, which have a much lower discharge rate and don't need to be at 100% SOC, users can get away with minimal maintenance charging if there are no parasitic draws on the battery, like the Bluetooth module.

How To Keep A Lithium-iron Phosphate Battery from Corroding?

Enjoybot batteries were designed with many features in the terminals to help fight corrosion for users. However, even with care and maintenance, batteries can be corroded over time. Users can minimize the rate of corroding with the steps below.

A simple way to reduce the effects of corrosion is to store lithium batteries in a cool and dry place. In addition to reducing corrosion, storing batteries under these conditions will increase the shelf life and life span of batteries.

Continuously inspecting the lithium battery terminals (if they appear dirty) and cleaning them with a soft dry cloth before using it, this can prevent a large buildup that may be difficult to remove later.

Conclusion

LiFePO4 chemistry lithium batteries have become more and more popular for a range of applications today due to being one of the most robust and long-lasting battery chemistries available. However, they will be damaged or early shorten their lifespan if users run them in the wrong way.