Modern equipment is becoming more complex and powerful day by day. High standards of technology place high demands on batteries, which now must combine high performance, energy efficiency and have an increased supply of electricity.
The introduction of new types of electrical equipment in production, the acceleration of the technological process - all this increases the requirements for electric power sources, and modern batteries can no longer always satisfy them. To solve this problem, manufacturers have taken the path of improving lithium-ion technology. Thus was born the lithium-iron-phosphate battery (LiFePO4), which is the ideological descendant of Li-ion batteries.
Historical reference
LiFePO4, or LFP, a natural mineral of the olivine family, was first discovered in 1996 by a scientist from the University of Texas at John Goodenough, who was looking for ways to improve Li-ion power sources. Noteworthy was the fact that this mineral had less toxicity and higher thermal stability than all the electrodes known at that time.
In addition, it was found in a natural environment and had a lower cost. The main disadvantage of electrodes based on LiFePO4 was the small electric capacity, which is why the lithium-iron-phosphate battery stopped developing.
Research in this direction was resumed in 2003 at the Massachusetts Institute of Technology. A team of scientists worked on the creation of a fundamentally new battery that would replace the most progressive Li-ion batteries at that time. Such large companies as Motorola and Qualcomm became interested in the project, which brought closer the appearance of batteries with LiFePO4 cathode cells.
LiFePO4 based battery
This type of rechargeable battery uses the same technology for generating electricity as the usual lithium-ion cells for us. However, there are a number of significant differences between them. Firstly, this is the use of its own type of BMS - a control system that protects electric batteries from overcharging and strong discharge, increases the service life and makes the energy source more stable.
Secondly, LiFePO4, in contrast to LiCoO2, is less toxic. This fact allowed us to avoid a number of problems associated with environmental pollution. In particular, to reduce cobalt emissions into the atmosphere during improper battery disposal.
Finally, due to the lack of common LFP standards, the elements have different chemical compositions, which leads to a variation in the technical characteristics of the models over a wide range. In addition, the maintenance of these power sources is more complex and must be subject to certain rules.
Specifications
It is worth saying that 48 Volt, 36 Volt and 60 Volt lithium-iron-phosphate batteries are made by connecting separate cells in series, because the maximum voltage in one LFP section cannot exceed 3.65 V. Therefore, the technical characteristics of each battery can significantly differ from each other - it all depends on the assembly and the specific chemical composition.
To analyze the technical characteristics, we give the nominal values of one individual cell.
The best implementation of the capabilities of each individual cell was achieved in the battery Everexceed. Everexceed lithium iron phosphate batteries have a long battery life. In total, they are able to withstand up to 4 thousand charge-discharge cycles with a loss of capacity of up to 20%, and replenishment of the energy reserve occurs in 12 minutes. Given this, it can be concluded that Everexceed batteries are some of the best representatives of LFP cells.
Advantages and disadvantages
The main advantage, which distinguishes the lithium-iron-phosphate battery from other representatives of the battery in a favorable light, is durability. Such an element is able to withstand more than 3 thousand cycles of charging and discharging when the energy level drops to 30%, and more than 2 thousand - when falling to 20%. Thanks to this, the average battery life is about 7 years.
Stable charge current is the second important advantage of LFP cells. The output voltage remains at 3.2 V until the charge is completely exhausted. This allows you to simplify the wiring diagram, eliminates the need for voltage regulators.
Higher peak current is their third advantage. This property of the battery allows them to give maximum power even at extremely low temperatures. This property prompted automakers to use a lithium-iron-phosphate battery as their primary source of energy when starting gasoline and diesel engines.
Along with all the advantages presented, LiFePO4 batteries have one significant drawback - their large mass and size. This limits their use in certain types of machinery and electrical equipment.
Operational Features
If you buy ready-made lithium-phosphate batteries, then you will have no difficulties with maintenance and operation. This is due to the fact that manufacturers integrate BMS boards in such elements that do not allow overcharging and do not allow the element to discharge to an extremely low level.
But if you purchase individual cells (finger batteries, for example), then you have to monitor the charge level yourself. When the charge falls below a critical level (below 2.00 V), the capacitance will rapidly fall, which will make it impossible to recharge the cells. If, on the contrary, you allow a recharge (above 3.75 V), the cell will simply swell due to the released gases.
If you use a similar battery for an electric car, then after 100% charge you need to disconnect the charger. Otherwise, the battery will swell due to oversaturation.
Terms of Use
If you plan to use lithium-phosphor batteries not in a cyclic mode, but in a buffer mode, for example, as a UPS power source or in conjunction with a solar battery, then you need to take care to lower the charge level to 3.40-3.45 V. Cope with This task is helped by “smart” chargers, which in automatic mode first fully replenish the energy supply, and then lower the voltage level.
During operation, you need to monitor the balance of the cells or use special balancing boards (they are already built into the battery for an electric car). An imbalance of cells is a condition when the total voltage of the device remains at the nominal level, but the voltage of the cells becomes different.
A similar phenomenon occurs due to the difference in resistance of individual sections, poor contact between them. If the cells have different voltages, then their charging and discharging unevenly occurs, which significantly reduces the battery life.
Putting batteries into operation
Before using lithium-phosphorus batteries assembled from separate cells, it is necessary to take care of balancing the system, since the sections can have different charge levels. To do this, all components are connected in parallel with each other and connected to the rectifier, charger. The cells connected in this way must be charged up to 3.6 V.
Using a lithium-iron-phosphate battery for an electric bike, you probably noticed that in the first minutes of operation the battery gives maximum power, and then the charge rapidly drops to a level of 3.3-3.0 V. Do not be afraid, this is normal battery operation . The fact is that its main capacity (about 90%) lies precisely in this range.
Conclusion
The efficiency of lithium phosphate batteries is 20-30% higher than that of other batteries. At the same time, they serve for 2-3 years longer than other sources of electricity, and also provide stable current throughout the entire period of operation. All this highlights the presented elements in a favorable light.
However, most people will ignore lithium iron phosphate batteries. The pros and cons of the battery fade before their price - it is 5-6 times more than the usual lead-acid elements for us. Such a battery for a car on average costs about 26 thousand rubles.