LiFepo4 battery

Lithium iron battery

Lithium iron phosphate battery is a kind of battery in lithium battery family. The cathode material is mainly lithium iron phosphate. Compared with traditional lead-acid batteries, lithium-ion batteries have significant advantages in working voltage, energy density and cycle life.


In 1990, Sony took the lead in introducing lithium-ion batteries with LiCoO 2 as cathode material in the laboratory, and began industrial production in 1991. Compared with traditional lead-acid batteries, lithium-ion batteries have significant advantages in working voltage, energy density and cycle life. Therefore, in the past two decades, lithium-ion batteries have been widely used in portable electronic devices, power tools and other fields. With the global attention to energy saving and emission reduction, lithium-ion batteries have been gradually applied in telecommunications, State Grid and electric vehicles and other industries. For energy saving and emission reduction in the telecommunication power supply industry, storage batteries are required to be smaller, lighter, longer life, higher temperature resistance, easier maintenance, more stable performance, and more environmentally friendly. In order to meet these needs, lithium-ion batteries are gradually changing to large capacity batteries, and lithium iron phosphate batteries for communication emerge as the times require. Iron-lithium battery is a kind of battery in lithium battery family. The cathode material is mainly lithium iron phosphate, also referred to as lithium-iron battery.

Safety Problem

Lithium-iron batteries are not as safe as some friends on the Internet have said. There is also a danger of explosion. Technology requires honesty and rigour.

The lithium iron phosphate battery 26650-3AH was overcharged at 3C10V, resulting in an explosion of the battery. Repeated tests showed similar results.

When the lithium battery is charged and discharged at high current, the internal temperature of the battery keeps rising, the gas generated in the activation process expands, the internal pressure of the battery increases, and the pressure reaches a certain level. If there is a scar in the shell, it will break down, causing leakage, fire and even explosion. Therefore, when you use it, you must pay attention to safety.

But in the normal use process, battery management system is usually used to protect power lithium batteries, so there is almost no explosion. However, for cell phone batteries, it is more likely to explode due to inadequate protective measures.

Working principle

The full name of lithium iron battery is lithium iron phosphate battery. Because its performance is particularly suitable for power applications, it is also called "lithium iron power battery". (hereinafter referred to as "lithium-iron battery")

Working Principle of Iron-Lithium Battery (LiFePO4)

The internal structure of LiFePO4 battery: olivine LiFePO4 is used as the positive pole of the battery on the left, which is connected with the positive pole of the battery by aluminium foil and polymer membrane in the middle. It separates the positive pole from the negative pole, but Li+ can pass through the electron e-but not through the negative pole of the battery composed of carbon (graphite) on the right, and copper foil is connected with the negative pole of the battery. Between the upper and lower ends of the battery is the electrolyte of the battery, which is sealed and encapsulated by a metal shell.

When LiFePO4 battery is charged, lithium ion Li + in positive electrode migrates to negative electrode through polymer diaphragm, and lithium ion Li + in negative electrode migrates to positive electrode through diaphragm during discharge. Lithium-ion batteries are named for the back-and-forth migration of lithium ions during charging and discharging.

Main Performance of LiFePO4 Battery

The nominal voltage of LiFePO4 battery is 3.2 V, the termination charge voltage is 3.6 V and the termination discharge voltage is 2.0 V. Because the quality and technology of positive and negative electrode materials and electrolyte materials used by various manufacturers are different, their performances will be different. For example, the capacity of the same type of battery (standard battery with the same package) is quite different (10%-20%).

Operation process

Lithium iron phosphate batteries are actually lithium-ion batteries with lithium iron phosphate as cathode data. For lithium-ion batteries, there are many kinds of cathode data, such as lithium cobalt oxide, lithium manganate, lithium nickel oxide, ternary information, lithium iron phosphate and so on. Lithium iron phosphate is the most commonly used information in lithium-ion industry.

Lithium iron phosphate batteries are connected by aluminum foil and the positive pole of batteries. On the left is the barrier of polymer, which separates the positive pole from the negative pole. But Li ion can start and end while electronic e-can not start and end. On the right is the negative pole of batteries composed of carbon, which is connected by copper foil and the negative pole of batteries. The upper and lower ends of batteries are electrolytes of batteries. The batteries are sealed by metal enclosures. LiFePO4 batteries are charged. In the process of discharge, the polymer barrier of lithium ion Li in the cathode moves to the cathode. In the process of discharge, the polymer barrier of lithium ion Li in the cathode moves to the cathode. Lithium ion batteries are named after lithium ion moving back and forth during charging and discharging.

The working principle of lithium-ion battery is that Li moves from 010 sides of lithium iron phosphate crystal to the crystal surface when the battery is charged. Under the effect of electric field, Li enters the electrolyte, crosses the barrier, then moves to the surface of graphite crystal through the electrolyte, and then embedded in the graphite lattice. After lithium ion is detached from lithium iron phosphate, lithium iron phosphate is transformed into iron phosphate; when the battery discharges, Li is transformed from graphite crystal. It is detached and embedded into the electrolyte. It crosses the barrier. Then it is moved to the surface of lithium iron phosphate crystal by electrolyte. Then it is embedded into the lattice of lithium iron phosphate through 010 plane. Then it is discharged by conducting current to the positive electrode of lithium iron phosphate.

For the conduction of positive and negative electrodes of quasi-lithium iron phosphate batteries, conductive agents must be added to the positive and negative electrodes of the batteries to make them constitute the active capital of the batteries. In the process of theoretical description and theoretical production, how to end the above three equations needs to be verified by a series of experiments. Mathematical models or curriculum vitae formulas should be established, and then these models or formulas should be established at the beginning and end to describe lithium-ion batteries.

At that time, the domestic lithium-ion batteries were old enough to have the world's leading level. At that time, the industry still focused on lithium-ion batteries with lithium iron phosphate as the cathode. Many countries developed new lithium-ion batteries. Only then did they not produce on a large scale. Some scholars pointed out that the lithium iron phosphate cathode data was an open mainstream industry in at least 10 years.

Battery characteristics

1. Efficiency output: standard discharge is 2-5C, continuous high current discharge can reach 10C, instantaneous pulse discharge (10S) can reach 20C;
2. Performances at high temperature are good: the internal temperature is as high as 95 ~C when the external temperature is 65 ~C, and the temperature at the end of battery discharge is as high as 160 ~C.
3. The safety of batteries has been improved to a certain extent, but it is not complete and still keep dangerous.
4. Good cycle life, after 500 cycles, its discharge capacity is still greater than 95%.
5. There is no safety problem from discharge to zero volt.
6. Fast charging;
7. Low cost;
8. No pollution to the environment.


Compared with traditional lead-acid batteries, lithium iron batteries have the following advantages: high energy density, high safety, high temperature performance, high power output, long cycle life, light weight, saving room reinforcement costs, small size, long battery life and good safety.

Battery comparison

Compared with traditional lead-acid batteries, lithium iron phosphate batteries have the following advantages:

(1) High energy density: nominal voltage is 3.2V, energy density is about 4 times that of lead-acid battery, small size and light weight;
(2) Strong security: lithium iron phosphate cathode material has good electrochemical performance, the charging and discharging platform is very stable, the structure is stable during charging and discharging, the battery does not burn, does not explode, and has good security;
(3) The high temperature performance is good: the battery works normally when the external temperature is 55 C;
(4) High power output: standard discharge is 0.2C and can be charged and discharged at 3C.
(5) Long cycle life: 1 C charge and discharge at room temperature, the capacity of monomer after 2000 cycles is still more than 80%.
(6) Environmental protection: The whole production process is clean and non-toxic, and all raw materials are non-toxic.

Compared with traditional lead-acid batteries, lithium iron phosphate batteries for communications can better reflect the needs of energy saving, material saving and land saving.

Discharge characteristics

Lithium iron phosphate power battery (here in after referred to as lithium iron battery) as a kind of iron battery, has been widely concerned by friends in the industry (some people say that lithium iron battery is actually a kind of lithium ion battery). As far as iron batteries are concerned, they can be divided into high iron batteries and iron-lithium batteries. Taking the type of iron-lithium batteries 18650 as an example, the discharge characteristics and life of iron-lithium batteries are described in detail.

The discharge characteristics of lithium-iron battery 18650 (capacity 1100 mAh) at different discharge rates. The minimum discharge rate is 0.5C and the maximum discharge rate is 10C. Five different discharge rates form a set of discharge curves. Whichever discharge rate, the discharge voltage is very flat (that is, the discharge voltage is stable, basically unchanged). Only when the discharge voltage is fast enough to terminate, the curve will bend downward (after discharge reaches 800 mAh, the curve will bend downward). In the discharge rate range of 0.5-10C, the output voltage mostly varies in the range of 2.7-3.2V. This shows that the battery has good discharge characteristics.

The discharge curves of 18650 with capacity of 1000 mAh at different temperatures (from - 20 to + 40 C). If the discharge capacity is 100% at 23 C, the discharge capacity decreases to 78% at 0 C, 65% at - 20 C and slightly more than 100% at + 40 C.

18650 lithium-iron batteries can work at - 20 C, but the output energy should be reduced by about 35%.

Charge-discharge cycle life curve of 18650. The charging and discharging cycle conditions are: charging at 1C charge rate, discharging at 2C discharge rate, and going through 570 charging and discharging cycles. After 570 charge-discharge cycles, the discharge capacity remains unchanged, indicating that the battery has a high life.

The lithium-iron power battery 18650 (1100mAh) was used to test the discharge to zero voltage. Test conditions: 1100 mAh 18650 battery was filled with 0.5C charge rate, and then discharged to 0 C battery voltage with 1.0C discharge rate. The batteries are divided into two groups: one group is stored for 7 days, the other group is stored for 30 days; after storage expires, the batteries are filled with 0.5C charge rate, and then discharged with 1.0C. Finally, the differences between the two zero-voltage storage periods are compared.

The test results show that after 7 days of zero voltage storage, the battery has no leakage, good performance and 100% capacity; after 30 days storage, the battery has no leakage, good performance and 98% capacity; after 30 days storage, the battery has three charge and discharge cycles, and the capacity restores to 100%.

This test shows that even if the battery is overdischarged (even up to 0V) and stored for a certain period of time, the battery will not leak or damage. This is a characteristic that other types of lithium-ion batteries do not possess.

Prospects for development

As a new battery technology, lithium-iron batteries have aroused great repercussions in the industry. Because lithium-iron batteries have many advantages and can produce batteries of different capacities, they are widely used. Here we list some of its main application areas and illustrate its superiority through a typical example:

Application area

1. Large-scale electric vehicles: buses, electric vehicles, sightseeing cars and hybrid electric vehicles, etc.
2. Light electric vehicles: electric bicycles, golf carts, small flat battery cars, forklifts, cleaning cars, electric wheelchairs, etc.
3. Electric tools: electric drills, electric saws, lawn mowers, etc.
4. Telecontrol toys such as automobiles, boats and airplanes;
5. Energy storage equipment for solar energy and wind power generation;
6. UPS and emergency lights, warning lights and mine lights (safety is the best);
7. Replace 3V disposable lithium battery and 9V nickel-cadmium or nickel-hydrogen rechargeable battery in camera (size is exactly the same).
8. Small medical instruments and portable instruments.

An application example of replacing lead-acid battery with iron-lithium power battery is given. Using 36V/10Ah (360Wh) lead-acid battery, its weight is 12kg, it can walk about 50km at one charge, the number of charges is about 100 times, and the service time is about one year. If the lithium-iron power battery is used and the same 360Wh energy (12 10Ah batteries in series) is used, its weight is about 4 kg, the charging time can be about 80 km, the charging times can reach 1000 times, and the service life can reach 3-5 years. Although the price of lithium-iron power batteries is much higher than that of lead-acid batteries, the overall economic effect of lithium-iron power batteries is better and lighter in use.

Iron-lithium battery is a new type of power battery. Because of its excellent performance, it attracts attention from all aspects. In our country, some factories have produced cathode materials for lithium-iron batteries and various kinds of iron-lithium-l power batteries with different capacities. However, this situation is expected to change in 2 to 3 years. Lithium-iron power batteries will be cheaper and more widely used, which will be the mainstream of power battery market in the future.

Application direction

(1) Outdoor Integrated Iron Battery Power Supply Solution

Outdoor communication base station is directly exposed to the sun. The life of built-in lead-acid batteries usually does not exceed 2 years. This scheme uses lithium iron phosphate batteries with excellent high temperature resistance and life of 5-10 years.

In this scheme, the advantages of battery, such as small size, light weight, high temperature resistance and long service life, can achieve the goal of energy saving and emission reduction in three aspects: energy saving, material saving and land saving, while effectively reducing maintenance and operation costs.

(2) Solutions for power supply of base station without air conditioning such as Murakami

The base stations of the village-to-village project are located in remote rural areas. They are small in scale and small in configuration. There are basically no air-conditioners. Moreover, power outages occur frequently. Lead-acid batteries work in harsh environments with short life, frequent replacement and high maintenance costs in remote rural areas. If iron batteries are used instead, they will have good high temperature performance, deep charging and discharging, long cycle life, small size, light weight and light installation. They can save energy, land and materials, and improve the quality of power supply in the network.

(3) Solution of power supply for indoor macro base station with tense space

The number of indoor macro base stations is large, covering a wide range of requirements for reliable power supply, so there are generally two sets of battery backup. Lead-acid batteries occupy a large area and weigh too much in the station. When the demand for capacity expansion is caused by the increase of traffic, the space in the station restricts the possibility of additional equipment.

If integrated switching power supply is used with iron batteries, the area occupied by power supply and batteries in the computer room can be reduced to meet the requirement of equipment expansion. At the same time, iron batteries have excellent high temperature resistance, which can raise the start-up temperature of air-conditioning in the station to about 35 degrees, reduce the energy consumption of air-conditioning, effectively reduce operating costs by saving electricity, and achieve the goal of energy saving, room saving and material saving.

(4) Indoor Coverage/Distributed Station Power Supply Solution

The number of indoor coverage stations will be further increased due to the original 2G network indoor coverage and the continuous construction of 3G and WLAN hotspots. Because the indoor coverage station usually chooses the local electricity nearby, choosing 48V communication battery module or iron battery UPS for standby can effectively solve this kind of problem.

(5) High Voltage Direct Current Power Supply System (HVDC) for Communication

Aiming at the power supply scheme of data center, industry experts put forward 240V/336V HVDC power supply system for communication. The characteristics of this system are high voltage (240V/336V), short time and high current discharge. If the stand-type lithium iron phosphate battery pack is used, the following advantages can be obtained:
(a) Light weight, saving reinforcing cost of machine room;
(b) Small size, can be placed side by side with HVDC system in the form of header cabinet, without the need to establish a separate battery room, can also save the area of power supply system, improve the probability of installation of communication equipment rack;
(c) Iron batteries can discharge at high rate and reduce the capacity of battery configuration.
(d) The discharging platform of iron batteries is stable, and the stable input voltage under the mode of battery power supply avoids the abnormality caused by the large range fluctuation of input voltage.
(6) Power Supply Scheme of Embedded UPS AC Power Supply System

For small and medium-sized data centers, developed countries in Europe and the United States also have an embedded UPS distributed power supply scheme, that is, using low-power UPS and network cabinet to cooperate with the cabinet as a unit of server power supply. UPS has the following advantages in choosing iron batteries:
(a) Light weight, saving reinforcing cost of machine room;
(b) Small size, 3KVA iron battery UPS only occupies 2U of the network cabinet space, improve the server installed rate;
(c) Long battery life, almost the same life of the main engine and battery, reducing the cost of battery replacement;
(d) Good safety, non-fire and non-explosion of iron batteries, meeting the high safety requirements of IDC computer room

Charging technology

Generally, constant voltage and current charging method is used. When the voltage of 3.2V nominal lithium-iron battery reaches 3.6V, it should stop charging immediately or maintain a very small charging current. When the voltage of lithium battery is very low, such as below 2V, trickle current charging can prolong the battery life.

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