Lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. The cathode materials of lithium-ion batteries are mainly lithium cobalt oxide, lithium manganate, lithium nickel oxide, ternary materials, lithium iron phosphate, etc. Among them, lithium cobalt oxide is the cathode material used in the vast majority of lithium-ion batteries.

working principle

The full name of lithium iron phosphate battery is lithium iron phosphate lithium ion battery, this name is too long, referred to as lithium iron phosphate battery. Because its performance is particularly suitable for power use, the word "power" is added to the name, that is, lithium iron phosphate power lithium battery. Some people also call it "Lithium Iron (LiFe) power lithium battery.

significance

In the metal trading market, cobalt (Co) is the most expensive, and there is not much storage, nickel (Ni) and manganese (Mn) are cheaper, and iron (Fe) is the cheapest. The prices of cathode materials are also in line with those 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.

As a rechargeable battery, the requirements are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, and safety in use (not due to overcharge, overdischarge and short circuit) It can cause combustion or explosion due to improper operation), wide operating temperature range, non-toxic or less toxic, and no pollution to the environment. The lithium iron phosphate battery using LiFePO4 as the positive electrode has good performance requirements, especially in terms of large discharge rate discharge (5 ~ 10C discharge), stable discharge voltage, safety (non-burning, non-exploding), life (cycle) In terms of no pollution to the environment, it is the best, and is currently the best high-current output power lithium battery.

Structure and working principle

LiFePO4 is used as the positive electrode of the battery, which is connected to the positive electrode of the battery by an aluminum foil, and the middle is a polymer separator, which separates the positive electrode from the negative electrode, but the lithium ion Li can pass through but the electron e- cannot pass through, and the right side is composed of carbon (graphite) The negative electrode of the battery 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 LiFePO4 batteries are charged, the lithium ions Li in the positive electrode migrate to the negative electrode through the polymer separator; during the discharge process, the lithium ions Li in the negative electrode migrate to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions migrate back and forth during charging and discharging.

Important performance

The nominal voltage of the LiFePO4 battery is 3.2V, the final charge voltage is 3.6V, and the final discharge voltage is 2.0V. Due to the different quality and process of positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the capacity of the battery of the same type (standard battery in the same package) is quite different (10% to 20%).

It should be noted here that lithium iron phosphate power lithium batteries processed by different factories will have some differences in various performance parameters; in addition, some battery performance is not included, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc. .

The capacity of lithium iron phosphate power lithium batteries is quite different and can be divided into three categories: small tenths to a few milliamp hours, medium tens of milliamp hours, and large hundreds of milliamp hours. There are also some differences in the same parameters of different types of batteries.

Overdischarge to zero voltage experiment

The STL18650 (1100mAh) lithium iron phosphate power lithium battery was used for the discharge to zero voltage experiment. Experimental conditions: Flood a 1100mAh STL18650 battery with a charge rate of 0.5C, and then discharge it to a battery voltage of 0C with a discharge rate of 1.0C. The batteries placed at 0V are then divided into two groups: one group is stored for 7 days, and the other group is stored for 30 days; after the storage expires, it is overflowed with a charging rate of 0.5C, and then discharged with 1.0C. Finally, the differences between the two zero-voltage storage periods are compared.

The result of the experiment is that after 7 days of zero voltage storage, the battery has no leakage, good performance, and the capacity is 100%; after 30 days of storage, there is no leakage, good performance, and the capacity is 98%; after 30 days of storage, the battery is subjected to 3 charge-discharge cycles, The capacity is back to 100%.

This experiment shows that even if the battery is over-discharged (even to 0V) and stored for a period of time, the battery will not leak or be damaged. This is a feature that other types of lithium-ion batteries do not have.

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