Working principle of lithium iron phosphate battery

LiFePO4 Prismatic Cells

The full name of lithium iron phosphate battery, LiFePO4 Prismatic Cells is lithium iron phosphate battery, which is too long. It is called lithium iron phosphate battery for short. As its performance is particularly suitable for power applications, the word "power" is added to the name, namely, lithium iron phosphate power battery. It is also known as "lithium iron power battery".

Structure and working principle:

LiFePO4 Prismatic Cells

The internal structure of LiFePO4 battery is shown in Figure 1. On the left is the olivine LiFePO4 as the positive electrode of the battery, which is connected by the aluminum foil and the positive electrode of the battery. In the middle is the polymer diaphragm, which separates the positive electrode from the negative electrode, but the lithium ion Li + can pass through but the electron e-cannot. On the right is the negative electrode of the battery composed of carbon (graphite), which is connected by the copper foil and the negative electrode of the battery. Between the upper and lower ends of the battery is the electrolyte of the battery, which is sealed and sealed by a metal shell.

During the charging of LiFePO4 battery, Li + in the positive electrode migrates to the negative electrode through the polymer membrane; during the discharging process, Li + in the negative electrode migrates to the positive electrode through the membrane. Lithium-ion batteries are named after the migration of lithium ions during charging and discharging.

LiFePO4 Prismatic Cells

Main performance:

The nominal voltage of LiFePO4 battery is 3.2V, the ending charging voltage is 3.6V and the ending 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, for the same model (standard battery with the same package), the capacity of the battery is quite different (10% - 20%).

The main performances of lithium iron phosphate power battery are listed in Table 1. In order to compare with other rechargeable batteries, the performance of other types of rechargeable batteries is also listed in the table. It should be noted that there will be some differences in the performance parameters of the lithium iron phosphate power battery produced by different factories; in addition, some battery performances are not included, such as internal resistance, self discharge rate, charge discharge temperature, etc.

LiFePO4 Prismatic Cells

Eight advantages of lithium iron phosphate battery

1. Improvement of safety performance

The P-O bond in lithium iron phosphate crystal is stable and hard to decompose. Even at high temperature or overcharge, it will not collapse and heat or form strong oxidizing substances like lithium cobaltic acid, so it has good safety. It has been reported that a small number of samples were found to burn in the acupuncture or short circuit experiment in the actual operation, but there was no explosion event. However, in the overcharge experiment, a high voltage charge which was several times more than its own discharge voltage was used, and the explosion phenomenon was still found. However, its overcharge safety has been greatly improved compared with the common liquid electrolyte lithium cobaltic acid battery.

2. Life improvement

Lithium iron phosphate battery is a kind of lithium-ion battery with lithium iron phosphate as cathode material.

The cycle life of long-life lead-acid battery is about 300 times, and the maximum is 500 times, while RJ lithium iron phosphate power battery LiFePO4 Prismatic Cells has a cycle life of more than 6000 times. The same quality lead-acid battery is "new half year, old half year, maintenance half year", and the maximum is 1-1.5 years, while the theoretical life of lithium iron phosphate battery under the same conditions will reach 7-8 years. Overall, the performance price ratio is more than 4 times that of lead-acid battery in theory. High current discharge can quickly charge and discharge high current 2C. Under the special charger, the battery can be fully charged within 40 minutes after charging 1.5C, and the starting current can reach 2c, while the lead-acid battery has no such performance now.

3. High temperature performance

The electrothermal peak value of lithium iron phosphate can reach 350 ℃ - 500 ℃, while that of lithium manganate and lithium cobaltite is only about 200 ℃. The working temperature range is wide (- 20C - + 75c), and the peak value of lithium iron phosphate with high temperature resistance can reach 350 ℃ - 500 ℃, while lithium manganate and lithium cobaltite are only around 200 ℃.

4. Large capacity

It has a larger capacity than ordinary batteries (lead acid, etc.). 5ah-1000ah (single)

5. No memory effect

Rechargeable batteries often work under the condition of being full and not being discharged, and the capacity will be rapidly lower than the rated capacity. This phenomenon is called memory effect. For example, Ni MH and Ni Cd batteries have memory, but the lithium iron phosphate battery does not have this phenomenon. No matter what state the battery is in, it can be charged and used at any time, without having to discharge it first and then charge it.

6. Light weight

The volume of lithium iron phosphate battery with the same capacity is 2 / 3 of that of lead-acid battery, and the weight is 1 / 3 of that of lead-acid battery.

7, environmental protection

The battery is generally considered to be free of any heavy metals and rare metals (NiMH batteries need rare metals), non-toxic (SGS certified), pollution-free, in line with European ROHS regulations, and is an absolute green environmental protection battery certificate.

However, some experts say that the environmental pollution caused by lead-acid batteries mainly occurs in the irregular production process and recycling process of enterprises. Similarly, lithium battery belongs to new energy industry, but it can not avoid heavy metal pollution. Lead, arsenic, cadmium, mercury and chromium may be released into dust and water during the processing of metal materials. The battery itself is a kind of chemical substance, so it may produce two kinds of pollution: one is the process waste pollution in the production engineering; the other is the battery pollution after being scrapped.

8. High current and fast discharge

It can be charged and discharged quickly with high current 2C. Under the special charger, the battery can be fully charged within 40 minutes with 1.5C charging, and the starting current can reach 2c, but the lead-acid battery has no such performance now.