1, improvement of safety performance
P-O bond in LiFePO4 crystal is stable and difficult to decompose. Even in the case of high temperature or overcharge, it will not collapse and generate heat or form strong oxidizing substances like lithium cobaltate, and the safety is good. It has been reported that a small number of samples were found to burn in the acupuncture or short-circuit experiment in actual operation, but no explosion occurred. In the overcharge experiment, it was found that there was still an explosion when charging with high voltage. Nevertheless, its overcharge safety has been greatly improved compared with the common liquid electrolyte lithium cobalt oxide battery.
2. Improve the service life
Lithium iron phosphate battery refers to a lithium ion battery with lithium ferrous phosphate as cathode material.
The cycle life of long-life lead-acid battery is about 300 times, and the maximum cycle life is 500 times, while the cycle life of lithium iron phosphate power battery is more than 2000 times, and the standard charging (5-hour rate) can reach 2000 times. The lead-acid battery with the same quality is "new half year, old half year and maintenance half year", and the longest time is 1~ 1.5 years, while the theoretical life of lithium iron phosphate battery will reach 7~8 years under the same conditions. Considering comprehensively, the cost performance ratio is theoretically more than four times that of lead-acid batteries. Large current discharge can charge and discharge quickly with large current 2C. Under the special charger, 1.5C can fully charge the battery within 40 minutes, and the starting current can reach 2C, but the lead-acid battery has no such performance.
3, good high temperature performance
The peak value of electric heating in Ferrous lithium phosphate can reach 350℃-500℃, while that of lithium manganate and lithium cobaltate is only about 200℃. The working temperature range is wide (-20℃-+75℃), and the Ferrous lithium phosphate peak electric heating with high temperature resistance can reach 350℃-500℃, while that of lithium manganate and lithium cobaltate is only about 200℃.
4. Large capacity
The capacity is larger than that of ordinary batteries (lead acid, etc.). ) .5ah-1000ah (monomer)
5. No memory effect
Rechargeable batteries often work when fully charged, and their capacity will soon drop below the rated capacity. This phenomenon is called memory effect. For example, Ni-MH and Ni-Cd batteries have memories, but lithium iron phosphate batteries do not. No matter what state the battery is in, it can be used while charging without first discharging and then charging.
6. Lightweight
The volume of lithium iron phosphate battery with the same specification and capacity is 2/3 of that of lead-acid battery, and its weight is 1/3 of that of lead-acid battery.
7. Environmental protection
Generally speaking, this battery is considered to be free of any heavy metals and rare metals (rare metals are required for Ni-MH batteries), non-toxic (certified by SGS), pollution-free, in line with European RoHS regulations, and is an absolute green battery certificate. Therefore, the reason why lithium batteries are favored by the industry is mainly due to environmental considerations. Therefore, the battery has been included in the national "863" high-tech development plan during the Tenth Five-Year Plan period and has become a key project supported and encouraged by the state. With China's entry into WTO, the export volume of electric bicycles in China will increase rapidly, and electric bicycles entering Europe and America have been required to be equipped with pollution-free batteries.
However, some experts said that the environmental pollution caused by lead-acid batteries mainly occurred in the irregular production process and recycling process of enterprises. Similarly, it is good that lithium batteries belong to the new energy industry, but the problem of heavy metal pollution cannot be avoided. Lead, arsenic, cadmium, mercury and chromium may be released into dust and water during the processing of metal materials. The battery itself is a chemical substance, so there may be two kinds of pollution: one is the pollution of process waste in production engineering; The second is the battery pollution after scrapping.
Lithium iron phosphate battery also has some disadvantages, such as poor low-temperature performance, low tap density of cathode materials, and the volume of lithium iron phosphate battery with the same capacity is larger than that of lithium ion batteries such as lithium cobalt oxide, so it has no advantage in miniature batteries. When lithium iron phosphate battery is used in power battery, it needs to face the problem of battery consistency like other batteries.
8. Comparison of power batteries
At present, the most promising cathode materials for power lithium ion batteries are modified lithium manganate (LiMn2O4), lithium ferrous phosphate (LiFePO4) and nickel cobalt lithium manganate (Li(Ni, Co, Mn)O2). Nickel-cobalt-lithium manganate ternary materials are generally considered to be difficult to become the mainstream of lithium-ion batteries for electric vehicles due to the lack of cobalt resources, high nickel-cobalt content and large price fluctuations, but they can be mixed with spinel lithium manganate in a certain range.
Second, the shortcomings of lithium iron phosphate battery
Whether a material has application and development potential depends not only on its advantages, but also on its fundamental defects.
At present, lithium ferrous phosphate is widely selected as the cathode material of power lithium ion batteries in China. Market analysts such as government, scientific research institutions, enterprises and even securities companies are optimistic about this material and regard it as the development direction of power lithium-ion batteries. There are two main reasons: first, influenced by the research and development direction of the United States, Valence and A 123 companies in the United States took the lead in adopting lithium iron phosphate as the cathode material of lithium ion batteries. Secondly, lithium manganate materials with good high-temperature cycling and storage performance for power lithium-ion batteries have not been prepared in China. However, lithium ferrous phosphate also has fundamental defects that cannot be ignored, which can be summarized as follows:
1. In the sintering process of preparing lithium ferrous phosphate, iron oxide can be reduced to elemental iron in a high-temperature reducing atmosphere. Elemental iron can cause micro-short circuit of battery, which is the most taboo substance in battery. This is also the main reason why Japan has not used this material as a cathode material for power lithium-ion batteries.
2. Lithium ferrous phosphate has some performance defects, such as low tap density and compaction density, which leads to low energy density of lithium ion batteries. Poor low temperature performance, even if nano-sized, carbon-coated, this problem has not been solved. Dr. DonHillebrand, director of the Energy Storage System Center of Argonne National Laboratory in the United States, described the low-temperature performance of lithium iron phosphate batteries as terrible. Their test results of lithium iron phosphate lithium ion batteries show that lithium iron phosphate batteries cannot drive electric vehicles at low temperatures (below 0℃). Although some manufacturers claim that the capacity retention rate of lithium iron phosphate battery is good at low temperature, this is under the condition of small discharge current and low discharge cut-off voltage. In this case, the equipment can't start working at all.
3. The preparation cost of this material is higher than that of the battery, and the battery yield is low and the consistency is poor. Although nano-LiFePO4 and carbon coating improve the electrochemical properties of the materials, they also bring other problems, such as decreased energy density, increased synthesis cost, poor electrode processability and harsh environmental requirements. Although the chemical elements Li, Fe and P in lithium ferrous phosphate are rich and cheap, the cost of the prepared lithium ferrous phosphate product is not low. Even if the previous research and development costs are removed, the process cost of materials and the higher cost of preparing batteries will make the final unit energy storage cost higher.
4. Poor product consistency. At present, there is no lithium ferrous phosphate material factory in China that can solve this problem. From the point of view of material preparation, the synthesis of lithium ferrous phosphate is a complex multiphase reaction, including solid phosphate, iron oxide and lithium salt, carbon precursor and reducing gas phase. In this complicated reaction process, it is difficult to ensure the consistency of the reaction.
5. Intellectual property rights. The earliest patent application for lithium ferrous phosphate was filed by Fxmittermeier &: SOEHNEOHG(DE) on June 25th, 1993, and the application result was announced on August 9th, 1993. The basic patent of lithium ferrous phosphate is from the University of Texas, while the patent of carbon coating is applied by Canadians. These two basic patents cannot be bypassed. If royalties are included in the cost, the product cost will further increase.