After so many years of development of LiFePO4 battery, I think everyone knows more or less about LiFePO4 battery, because many products in life use batteries that are powered by LiFePO4 battery, but many people do not have a deep understanding. It, today we will talk about the structure, working principle, characteristics, application scope of LiFePO4 battery and LiFePO4 battery in depth, as well as the most popular LiFePO4 power station in recent years.
What is LiFePO4 battery
The full name of LiFePO4 battery should be lithium iron phosphate lithium ion battery, or LiFePO4 battery for short. It is a lithium ion battery that uses LiFePO4 material as the positive electrode of the battery. It is a product launched after 2002 and is a new member of the lithium ion battery family. Because its performance is particularly suitable for power applications, the word "power" is added to the name, that is, lithium iron phosphate power battery. Some people call it "LiFe power battery".
The current lithium ion battery cathode material on the market is mainly LiCoO2. In addition, there are a few lithium-ion batteries that use LiMn2O4 and LiNiO2 as cathode materials. Generally, the lithium-ion batteries of the latter two cathode materials are called "lithium manganese batteries" and "lithium manganese batteries". Nickel battery". Among the metal elements composing the positive electrode material of the battery, Co is the most expensive and has a small storage capacity. Ni and Mn are cheaper, while Fe is the cheapest. The price of the cathode material is also consistent with the price of these metals. Therefore, the lithium ion battery made of LiFePO4 cathode material should be the cheapest. Another feature of it is that it does not pollute the environment.
LiFePO4 battery is a rechargeable battery that has high capacity, high output voltage, good charge-discharge cycle performance, stable output voltage, high-current charge and discharge, electrochemical stability, and safety in use (no overcharge or over Improper operation such as discharge and short circuit can cause combustion or explosion), wide operating temperature range, non-toxic or less toxic, and no pollution to the environment. These performance requirements are good, especially for high discharge rate discharge (5～10C discharge), discharge voltage It is the best in terms of stability, safety (no combustion, no explosion), life (number of cycles), and no pollution to the environment. It is currently the best high-current output power battery.
The structure and working principle of LiFePO4 battery
The internal structure of LiFePO4 battery is shown in the figure below. On the left is LiFePO4 with olivine structure as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil. In the middle is a polymer separator, which separates the positive electrode from the negative electrode. The negative electrode of the battery composed of carbon (graphite) is connected to the negative electrode of the battery by copper foil. Between the upper and lower ends of the battery is the electrolyte of the battery, and the battery is hermetically sealed by a metal casing.
When the LiFePO4 battery is charged, the lithium ion Li+ in the positive electrode migrates to the negative electrode through the polymer separator; during the discharge process, the lithium ion Li+ in the negative electrode migrates to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions move back and forth during charging and discharging.
The nominal voltage of LiFePO4 battery is 3.2 V, the final charging voltage is 3.6V, and the final discharge voltage is 2.0V. Due to the different quality and technology of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the battery capacity of the same model (standard battery in the same package) is quite different (10%-20%).
In order to compare with other rechargeable batteries, the performance of other types of rechargeable batteries is also listed in the table. What I want to explain here is that LiFePO4 batteries produced by different factories have some differences in various performance parameters; in addition, there are some battery performances that are not listed, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc.
The capacity of LiFePO4 battery is quite different, which can be divided into three categories: small-scale a few to several milliamp-hours, medium-scale tens of milliamp-hours, and large-scale hundreds of milliamp-hours. Similar parameters of different types of batteries also have some differences. Here we will introduce the parameters of a small standard cylindrical packaged lithium iron phosphate power battery that is currently widely used. Its external dimensions: diameter 18mm, height 650mm (model 18650).
2. Good performance at high temperature: when the external temperature is 65 ℃, the internal temperature is as high as 95 ℃, and the temperature can reach 160 ℃ at the end of the battery discharge. The structure of the battery is safe and intact;
3. Even if the battery is injured internally or externally, the battery does not burn or explode, and has the best safety;
4. Excellent cycle life, after 500 cycles, its discharge capacity is still greater than 95%;
5. There is no damage even after over-discharge to zero volts;
6. Can be charged quickly;
7. Low cost;
8. No pollution to the environment.
Because LiFePO4 battery has the above-mentioned characteristics, and produces batteries of different capacities, it is quickly widely used. Its main application areas are:
1. Large-scale electric vehicles: buses, electric vehicles, tourist attractions and hybrid vehicles, etc.;
2. Light electric vehicles: electric bicycles, golf carts, small flat battery carts, forklifts, cleaning vehicles, electric wheelchairs, etc.;
3. Power tools: electric drills, electric saws, lawn mowers, etc.;
4. Remote control cars, boats, airplanes and other toys;
5. Energy storage equipment for solar and wind power generation;
6. UPS and emergency lights, warning lights and miner's lamps (the best safety);
7. Replace the 3V disposable lithium battery and 9V nickel-cadmium or nickel-metal hydride rechargeable batteries in the camera (the same size);
8. Small medical equipment and portable equipment, etc.
LiFePO4 battery has a series of unique advantages such as high working voltage, high energy density, long cycle life, and environmental protection, and supports unlimited expansion. After forming an energy storage system, it can be used for large-scale electrical energy storage. LiFePO4 power station is composed of LiFePO4 battery pack, Battery Management System, BMS, converter device (rectifier, inverter), central monitoring system, transformer, etc.
In the charging stage, the intermittent power supply or the grid charges the energy storage system. The AC power is rectified into DC after the rectifier to charge the energy storage battery module and store energy; in the discharge stage, the energy storage system discharges to the grid or load, and the energy storage battery module The DC power is converted to AC power through the inverter, and the inverter output is controlled by the central monitoring system, which can provide stable power output to the grid or load.
The LiFePO4 power station has a large capacity, much larger than that of a lithium battery. It is environmentally friendly and has a long lifespan. It is also resistant to high temperatures. However, some users have responded that not all LiFePO4 power stations are very good. I think the LiFePO4 power stations selected by these users are provided by relatively poor suppliers, because the materials and methods used to make the LiFePO4 power station are not correct, the user's use effect is not good. Here is a recommendation to use ITEHIL power station.
Friendly reminder: ITEHIL LiFePO4 power station works better with ITEHIL solar panel!