Lithium iron phosphate batteries The full name is lithium iron phosphate Lithium-ion batteries This name is too long and is referred to as Lithium Iron Phosphate. As 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 also call it "lithium iron (LiFe) power battery".

Working Principles

Lithium iron phosphate battery refers to the lithium-ion battery using lithium iron phosphate as the positive electrode material. The main cathode materials for lithium-ion batteries are lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and so on. Among them, lithium cobaltate is currently the majority of lithium-ion battery cathode materials used.

Significance

On the metal exchange, cobalt (Co) is the most expensive and is not stored in large quantities, nickel (Ni) and manganese (Mn) are cheaper, while iron (Fe) is stored in large quantities. The price of the cathode material is also in line with the price quotes for these metals. Therefore, lithium-ion batteries made with LiFePO4 cathode material should be quite cheap. Another feature of it is that it is environmentally friendly and non-polluting to the environment.

As a rechargeable battery requirements are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, safety in use (not due to overcharge, over discharge and short circuit and other improper operation caused by combustion or explosion), wide operating temperature range, non-toxic or less toxic, no pollution of the environment. LiFePO4 as the positive electrode of lithium iron phosphate in these performance requirements are good, especially in the large discharge rate discharge (5 ~ 10C discharge), smooth discharge voltage, safety (no combustion, no explosion), life (the number of cycles), no pollution to the environment, it is the best, is the best current high output power battery.

Structure and working principles

LiFePO4 is used as the positive end of the battery and is connected to the positive end of the battery by an aluminium foil. In the middle is a polymeric diaphragm which separates the positive end from the negative end, but through which the lithium ion Li can pass but not the electron e-. On the right side is the negative end of the battery which consists of carbon (graphite) and is connected to the negative end of the battery by a copper foil. Between the top and bottom of the cell is the electrolyte of the cell, which is hermetically sealed by a metal casing.

In LiFePO4 batteries, the lithium ion Li in the positive electrode migrates through the polymer diaphragm towards the negative electrode during charging; during discharge, the lithium ion Li in the negative electrode migrates through the diaphragm towards the positive electrode. Li-ion batteries are named after lithium ions that migrate back and forth during charging and discharging.

Key performance

LiFePO4 batteries have a nominal voltage of 3.2 V, an end charge voltage of 3.6 V and an end discharge voltage of 2.0 V. Due to differences in the quality and process of the positive and negative electrode materials and electrolyte materials used by each manufacturer, there are some differences in performance. For example, the capacity of the same model (standard battery in the same package) varies considerably (10% to 20%).

It should be noted here that there will be some differences in the various performance parameters of lithium iron phosphate power batteries produced by different factories; in addition, there are some battery properties not included, such as internal resistance, self-discharge rate, charge and discharge temperature of the battery.

The capacity of lithium iron phosphate power batteries varies considerably and can be divided into three categories: small ones with a few zeroes to a few mAh, medium ones with a few tens of mAh and large ones with a few hundred mAh. There are also some differences in similar parameters between the different types of batteries.

Over-discharge to zero voltage test.

A discharge to zero voltage test was done using a STL18650 (1100mAh) lithium iron phosphate power cell. Test conditions: The 1100mAh STL was charged with a 0.5C charge rate, then discharged with a 1.0C discharge rate until the battery voltage was 0C.Titan's battery The batteries were then divided into two groups: one group was stored for 7 days and the other group was stored for 30 days; after the expiry of the storage period, the batteries were filled with a 0.5C charge rate and then discharged with 1.0C. Finally, compare the difference between the two types of zero voltage storage periods.

The results of the test were that after 7 days of zero voltage storage the battery had no leaks, good performance and 100% capacity; after 30 days of storage there were no leaks, good performance and 98% capacity; after 30 days of storage the battery then did 3 charge/discharge cycles and the capacity was back to 100%.