Lithium iron phosphate battery's full name is lithium iron phosphate lithium-ion battery, which is too long, referred to as lithium iron phosphate battery. Because its performance is particularly suitable for power applications, it is added to the name of the word "power", that is, lithium iron phosphate power battery. Some people also call it a "lithium-iron (LiFe) power battery".
Working principle
Lithium iron phosphate battery refers to the lithium-ion battery with lithium iron phosphate as the cathode material. Lithium-ion battery cathode materials are mainly lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate, etc.. Among them, lithium cobaltate is the cathode material used in the majority of lithium-ion batteries at present.
Significance
In the metal trading market, cobalt (Co) is expensive and not much stored, nickel (Ni) and manganese (Mn) are cheaper, while the iron (Fe) is more stored. The price of the cathode material is also consistent with the price quotations of these metals. Therefore, the lithium-ion battery made of 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 overcharging, 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 battery 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 (number of cycles), no pollution to the environment, it is good, is currently a good high current output power battery.
Structure and working principle
LiFePO4 as the positive electrode of the battery is connected by aluminum foil to the positive electrode of the battery, in the middle is the diaphragm of polymer, which separates the positive electrode from the negative electrode, but lithium-ion Li can pass while electron e- cannot pass, and the negative electrode of the battery is composed of carbon (graphite) on the right, which is connected by copper foil to the negative electrode of the battery. Between the upper and lower ends of the battery is the electrolyte of the battery, which is hermetically encapsulated by a metal shell. liFePO4 battery during charging, the lithium-ion Li in the positive electrode migrates to the negative electrode through the polymer diaphragm; during discharging, the lithium-ion Li in the negative electrode migrates to the positive electrode through the diaphragm. Li-ion batteries are named after the lithium ions that migrate back and forth during charging and discharging.
Main performance
The nominal voltage of the LiFePO4 battery is 3.2V, the termination charging voltage is 3.6V, and the termination discharging voltage is 2.0V. Due to the different quality and processes of positive and negative electrode materials and electrolyte materials used by each manufacturer, there are some differences in its performance. For example, the same model (standard battery in the same package) has a large difference (10% to 20%) in its battery capacity.
It should be noted here that different factories that produce lithium iron phosphate power batteries in the various performance parameters will have some differences; in addition, there are some battery performance is not included, such as battery resistance, self-discharge rate, charge, and discharge temperature, etc..
Lithium iron phosphate power battery capacity has a large difference, can be divided into three categories: small zero-point a few to a few mAh, medium-sized tens of mAh, large hundreds of mAh. Similar parameters of different types of batteries also have some differences.
Over-discharge to zero voltage test: STL18650 (1100mAh) lithium iron phosphate power battery was used to do the discharge to zero voltage test.
Test conditions: use a 0.5C charge rate to fill the 1100mAh STL18650 battery, and then use a 1.0C discharge rate to discharge the battery voltage to 0C. Then the battery will be put into two groups of 0V: one group stored for 7 days, and the other group stored for 30 days; after the expiration of storage and then use 0.5C charge rate to fill, and then use 1.0C discharge. Compare the difference between the two types of zero-voltage storage periods different.
The result of the test is that after 7 days of zero-voltage storage battery no leakage, good performance, the capacity of 100%; after 30 days of storage, no leakage, good performance, the capacity of 98%; after 30 days of storage battery and then do 3 charge and discharge cycles, the capacity is back to 100%. This test shows that the lithium iron phosphate battery even if over-discharge (even to 0V), and stored for a certain period of time, battery does not leak, damage. These is other types of lithium-ion batteries that do not have the characteristics.
Advantages:
1, safety performance improvement lithium iron phosphate crystals in the P-O bond are stable, difficult to decompose, even at high temperatures or overcharge will not be as hot as lithium cobalt acid structure collapse or the formation of strong oxidizing substances, so it has good safety. There is a report that a small number of samples were found to be burning in the pinprick or short-circuit test, but there was no case of explosion, while there was still an explosion in the overcharge test when it was charged with a high voltage that greatly exceeded its own discharge voltage by several times. Despite this, its overcharge safety compared to ordinary liquid electrolyte lithium cobalt-acid batteries has been greatly improved.
2, the improvement of life lithium iron phosphate batteries are lithium-ion batteries with lithium iron phosphate as the cathode material. Long-life lead-acid battery cycle life of about 300 times, high also 500 times, and lithium iron phosphate power battery, the cycle life of more than 2000 times, the standard charge (5-hour rate) use, can reach 2000 times. The same quality of lead-acid batteries are "new six months, old six months, maintenance and six months", more than 1 to 1.5 years, while lithium iron phosphate batteries used under the same conditions, the theoretical life will reach 7 to 8 years. Considered together, the performance-to-price ratio is theoretically more than four times that of lead-acid batteries. High-current discharge can be high current 2C rapid charge and discharge, in a special charger, 1.5C charging within 40 minutes can make the battery full, starting current up to 2C, while the lead-acid batteries do not have this performance.
3, the high-temperature performance of lithium iron phosphate electric peak of 350 ℃ -500 ℃ and lithium manganate and lithium cobalt acid only in about 200 ℃. Wide operating temperature range (-20C- 75C), high-temperature resistance lithium iron phosphate peak electrical heating up to 350 ℃ -500 ℃ and lithium manganate and lithium cobalt acid only in about 200 ℃.
4, high-capacity ∩ rechargeable batteries in often in the full not put out under the conditions of work, the capacity will quickly fall below the rated capacity value, this phenomenon is called the memory effect. Like nickel-metal hydride, nickel-cadmium batteries have memory, while lithium iron phosphate batteries do not have this phenomenon, no matter what state the battery is in, can be used as it is charged, no need to first put out and then charged.
5, lightweight
The same capacity of lithium iron phosphate battery volume is the volume of lead-acid batteries 2 / 3, the weight of lead-acid batteries 1 / 3.
6, environmental protection
Lithium iron phosphate batteries are generally considered to be free of any heavy metals and rare metals (NiMH batteries require rare metals), non-toxic (SGS certification through), non-polluting, in line with European RoHS regulations, for the absolute green battery certificate. So lithium batteries are favored by the industry, mainly because of environmental considerations, so the battery was included in the "863" national high-tech development plan during the "Tenth Five-Year Plan", becoming key national support and encouraging the development of the project.
With China's accession to the WTO, the export volume of Chinese electric bicycles will increase rapidly, and the electric bicycles entering Europe and America are required to be equipped with non-polluting batteries. However, some experts say that the environmental pollution caused by lead-acid batteries mainly occurs in the enterprise's unregulated production process and recycling treatment.
Similarly, lithium batteries belonging to the new energy industry is good, but it can not avoid the problem of heavy metal pollution. Metal material processing has lead, arsenic, cadmium, mercury, chromium, etc. are likely to be released into the dust and water.
The battery itself is a chemical substance, so there may be two kinds of pollution: one is the production engineering process excretion pollution; the second is the battery pollution after the end of life. Lithium iron phosphate batteries also have their drawbacks: for example, poor low-temperature performance, cathode material vibranium density is small, the volume of lithium iron phosphate batteries of equal capacity is larger than lithium cobalt acid and other lithium-ion batteries, so it does not have an advantage in micro-batteries. And for power batteries, lithium iron phosphate batteries and other batteries, like other batteries, need to face the problem of battery consistency.
