Spatial Structure Of Lifepo4 Battery – Solar Generators

Our solar generators use LiFePO4 batteries, which have strong thermal and chemical stability and can improve the safety of the batteries. The lithium iron phosphate batteries provide SOUOP portable power stations with 2500 cycles and a battery life of more than 10 years.

LiFePO4 battery

Overview of LiFePO4 Batteries

LiFePO4 battery refers to a lithium ion battery using LiFePO4 as a positive electrode material. The cathode materials of LiFePO4 batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickel oxide, ternary materials, LiFePO4, etc. Among them, lithium cobalt oxide is the cathode material used in the vast majority of LiFePO4 batteries.

Spatial structure of LiFePO4 battery

For the cathode material of LiFePO4, its raw material sources are relatively wide, the cycle life is long, the safety index is also high, and the environmental pollution is small. Hotspot materials, under the development in recent years, LiFePO4 type cathode materials have reached a practical level, and even began to be formally commercialized. LiFePO4 is an olivine structure, the spatial structure is shown in Figure 1, and its theoretical specific capacity is 170mAhh, when the lithium-ion battery is charged, an oxidation reaction occurs, and the lithium ions FeO6 are released between the layers, flow into the electrolyte, and finally reach the negative electrode. In the external circuit, the electrons reach the negative electrode at the same time, and the iron will change from ferrous ions to ferric ions. , an oxidation reaction occurs. The discharge process is the opposite of the charging process, and a reduction reaction occurs.

Spatial structure of LiFePO4
Spatial structure of LiFePO4

The working principle of LiFePO4 battery:

LiFePO4 battery refers to a lithium ion battery using LiFePO4 as a positive electrode material. The cathode materials of LiFePO4 batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickel oxide, ternary materials, LiFePO4, etc. Among them, lithium cobalt oxide is the cathode material used in the vast majority of LiFePO4 batteries.

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) has more storage. The prices of cathode materials are also in line with those of these metals. Therefore, LiFePO4 batteries made of LiFePO4 cathode materials should be quite cheap. Another feature of it is that it is environmentally friendly and non-polluting.

As a rechargeable battery, the requirements are: high capacity, high output voltage, good charge-discharge cycle performance, stable output voltage, high-current charge-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. LiFePO4 batteries using LiFePO4 as the positive electrode have good performance requirements, especially in terms of large discharge rate discharge (5 ~ 10C discharge), stable discharge voltage, safety (non-burning, non-exploding), life (cycle times) ), no pollution to the environment, it is the best, and is currently the best high-current output power 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 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. LiFePO4 batteries are named after lithium ions migrate back and forth during charging and discharging.

Main 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 electrode 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 LiFePO4 power batteries produced 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 LiFePO4 power 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.

Over-discharge to zero voltage test:

The STL18650 (1100mAh) LiFePO4 power battery was used for the discharge to zero voltage test. Test conditions: 1100mAh STL18650 battery is fully charged with a 0.5C charge rate, and then discharged to a battery voltage of 0C with a 1.0C discharge rate. Then divide the batteries placed at 0V 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 fully charged with a 0.5C charging rate, and then discharged with 1.0C. Finally, the differences between the two zero-voltage storage periods are compared.

The result of the test 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 test shows that even if the LiFePO4 battery is over-discharged (even to 0V) and stored for a certain period of time, the battery will not leak or be damaged. This is a feature that other types of LiFePO4 batteries do not have.

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