Lithium-iron-phosphate battery: characteristics, application

Modern equipment day by day is becoming more complex and powerful. High standards of technology put 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 into production, the acceleration of the technological process - all this increases the requirements for electric power sources, and modern batteries can not always satisfy them. To solve this problem, manufacturers have followed the path of improving lithium-ion technology. Thus, a lithium-iron-phosphate battery (LiFePO4), which is the ideological descendant of Li-ion batteries, was born.

Historical reference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, John Goodenough, who was looking for ways to improve Li-ion sources of electricity. Noteworthy was the fact that this mineral had less toxicity and higher thermal stability than all known electrodes at the time.

In addition, he met in the natural environment and had a lower cost. The main drawback of electrodes based on LiFePO4 is a small electrical capacitance, which is why the lithium-iron-phosphate battery ceased to be developed.

Research in this direction was resumed in 2003 at the Massachusetts Institute of Technology. The team of scientists worked on creating fundamentally new batteries that would replace the most advanced at that time Li-ion batteries. The project was interested in such large companies as Motorola and Qualcomm, which brought the appearance of batteries with LiFePO4 cathode elements.

Battery based on LiFePO4

This type of battery uses the same technology to generate electricity as the usual lithium-ion cells. However, there are a number of significant differences between them. Firstly, it is the use of a proprietary type of BMS, a control system that protects electric accumulators from overcharging and strong discharge, increases the service life and makes the energy source more stable.

Secondly, LiFePO4, unlike LiCoO2, is less toxic. This fact has allowed to avoid a number of problems related to environmental pollution. In particular, to reduce emissions of cobalt in the atmosphere with improper disposal of batteries.

Finally, due to the lack of unified standards for LFP elements have different chemical composition, which causes variation in the technical characteristics of models in a wide range. In addition, the maintenance of these power supplies is more complex and must be done in accordance with certain rules.

Specifications

It should be noted that lithium-phosphate batteries 48 Volt, 36 Volts and 60 Volts are manufactured by means of consecutive interconnection of individual cells, since the maximum voltage in one LFP-section can not exceed 3.65 V. Therefore, the technical indicators of each battery can significantly Differ from each other - it all depends on the assembly and the specific chemical composition.

For the analysis of technical characteristics, we give the nominal values of one individual cell.

The best realization of the capabilities of each individual cell was achieved in the battery Everexceed. Everexceed lithium-phosphate batteries have a long service life. In total, they are able to withstand up to 4 thousand charge-discharge cycles with a capacity loss of up to 20%, and the energy reserve is replenished in 12 minutes. Given this, it can be concluded that Everexceed batteries are among the best representatives of LFP-elements.

Advantages and disadvantages

The main advantage, which favorably distinguishes the lithium-iron-phosphate battery among other representatives of the battery, is longevity. Such an element is able to withstand more than 3 thousand charge-discharge cycles when the level of electricity falls to 30%, and more than 2 thousand - with a fall to 20%. Due to this, the average battery life is about 7 years.

Stable charge current is the second important advantage of LFP elements. The output voltage remains at 3.2 V until the charge is completely depleted. This allows you to simplify the wiring diagram, eliminates the need for using voltage regulators.

A higher peak current is their third advantage. This property of the battery allows them to give out the maximum power even at extremely low temperatures. This feature prompted car makers to use the lithium-iron-phosphate battery as the primary source of energy when starting gasoline and diesel engines.

Along with all the advantages presented, LiFePO4 batteries have one significant drawback - a large mass and size. This limits their use in certain types of equipment and electrical equipment.

Features of operation

If you buy ready-made lithium-phosphate batteries, then you will not have any difficulties with maintenance and operation. All thanks to the fact that manufacturers build in such elements of BMS cards that do not allow overcharging and do not allow to discharge the element to the lowest possible level.

But if you get individual cells (finger batteries, for example), then you have to monitor the charge level yourself. If the charge drops below the critical level (below 2.00 V), the capacitance will also drop rapidly, 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 because of 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 excessive electric current.

Rules of operation

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 together with a solar battery, then you need to take care of lowering the charge level to 3.40-3.45 V. To cope with This task is helped by "smart" chargers, which in the automatic mode first completely fill up the energy reserve, and then lower the voltage level.

During operation, you need to monitor the balance of the cells or use special balancing cards (in the battery for the electric car they are already built in). An imbalance of cells is the state 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 resistances of individual sections, poor contact between them. If the cells have different voltages, then they are unequally charged and discharged, which significantly reduces the battery life.

Putting batteries into operation

Before using lithium-phosphor batteries assembled from separate cells, care must be taken to balance the system, since sections may have different levels of charge. To do this, all components are connected in parallel and connect to the rectifier, charger. The cells thus connected 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 the maximum power, and then the charge rapidly drops to a level of 3.3-3.0 V. Do not be frightened, because this is the normal operation of the battery . 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. In this case, they serve 2-3 years longer than other sources of electricity, and also provide a stable current throughout the life of the operation. All this highlights the presented elements in a favorable light.

However, most people will ignore lithium-iron-phosphate batteries. The advantages and disadvantages of the battery are dimmed before their price - it is 5-6 times more than in the lead-acid elements that are habitual for us. This battery for the car on average costs about 26 thousand rubles.