Since the advent of lithium-ion batteries, research and development work around it has continued. In the late 1990s, lithium polymer batteries were developed. After 2002, lithium iron phosphate power batteries were introduced.
The interior of a lithium ion battery is mainly composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The difference in the positive and negative electrodes and electrolyte materials and the difference in process make the battery have different performance and have different names. At present, the cathode material of lithium ion battery on the market is mainly lithium cobalt oxide (LiCoO2), and a few lithium ion batteries using lithium manganese oxide (LiMn2O4) and lithium nickel oxide (LiNiO2) as positive electrode materials, generally the latter two positive electrodes. The lithium ion battery of the material is called "lithium manganese battery" and "lithium nickel battery". The newly developed lithium iron phosphate power battery is a lithium ion battery using lithium iron phosphate (LiFePO4) material as the positive electrode of the battery, and it is a new member of the lithium ion battery family.
Generally, the electrolyte of a lithium ion battery is liquid. Later, a solid-state and gel-type polymer electrolyte was developed. This lithium-ion battery is called a lithium polymer battery, and its performance is superior to that of a liquid electrolyte lithium ion battery.
The full name of lithium iron phosphate battery should be lithium iron phosphate lithium ion battery, the name is too long, referred to as lithium iron phosphate battery. Because its performance is particularly suitable for power applications, the word "power" is added to the name, namely lithium iron phosphate power battery. Some people call it "LiFe iron (LiFe) power battery."
The significance of using LiFePO4 material as positive electrode
The cathode materials currently used as lithium ion batteries are mainly LiCoO2, LiMn2O4, LiNiO2 and LiFePO4. Among these metal elements constituting the positive electrode material of the battery, cobalt (Co) is the most expensive, and the storage amount is small, nickel (Ni) and manganese (Mn) are relatively inexpensive, and iron (Fe) is the cheapest. The price of the cathode material is also consistent with the price of these metals. Therefore, a lithium ion battery made of a LiFePO4 positive electrode material should be the cheapest. Another feature of it is that it is environmentally friendly.
The requirements for rechargeable batteries are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, and safety during use (not overcharged, overdischarged, and Short-circuit or other improper operation causes combustion or explosion), wide operating temperature range, non-toxic or less toxic, no pollution to the environment. Lithium iron phosphate battery using LiFePO4 as positive electrode has good performance requirements, especially in large discharge rate discharge (5~10C discharge), stable discharge voltage, safety (no combustion, no explosion), and life (cycle number) ), it is the best for the environment, it is the best high current output power battery.
Structure and working principle of LiFePO4 battery
The internal structure of the LiFePO4 battery is shown in Figure 1. On the left is the olivine-structured LiFePO4 as the positive electrode of the battery. The aluminum foil is connected to the positive electrode of the battery. The middle is the polymer separator. It separates the positive electrode from the negative electrode, but the lithium ion Li+ can pass and the electron e- cannot pass. The right side is composed of A battery negative electrode composed of carbon (graphite) is connected to the negative electrode of the battery by a 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.
Figure 1 Internal structure of LiFePO4 battery
When the LiFePO4 battery is charged, the lithium ion Li+ in the positive electrode migrates toward the negative electrode through the polymer separator; during the discharge, the lithium ion Li+ in the negative electrode migrates toward the positive electrode through the separator. Lithium-ion batteries are named after the lithium ions migrate back and forth during charging and discharging.
LiFePO4 battery main performance
The nominal voltage of the LiFePO4 battery is 3.2 V, the termination charging voltage is 3.6 V, and the termination discharge voltage is 2.0 V. Due to the quality and process of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the same model (standard battery of the same package) has a large difference in battery capacity (10% to 20%).
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