1、Improvement of safety performance
Lithium iron phosphate crystals in the P-O bond is stable, difficult to decompose, even at high temperatures or overcharge will not be like lithium cobaltate structure collapse and heat or the formation of strong oxidizing substances, so it has a 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, the overcharge safety has been greatly improved compared with the ordinary liquid electrolyte lithium cobalt acid battery.
2, the improvement of life
Lithium iron phosphate battery is a lithium-ion battery with lithium iron phosphate as the cathode material.
Long-life lead-acid battery cycle life of about 300 times, up to 500 times, and lithium iron phosphate power battery, 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 maintenance and six months", at most 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, high temperature performance
Lithium iron phosphate electric heat peak up to 350 ℃ -500 ℃ and lithium manganate and lithium cobalt acid only in about 200 ℃. Wide operating temperature range (-20C - 75C), with high temperature resistance lithium iron phosphate peak electrical heating up to 350 ℃ -500 ℃ and lithium manganate and lithium cobalt only in about 200 ℃.
4, large capacity
Although the capacity of lithium iron phosphate and ternary lithium batteries compared to the capacity of any gap, but because of its greater stability, so it is more suitable for making high-capacity monoblock batteries.
6, light weight
The same size capacity of lithium iron phosphate battery volume is 2/3 of the volume of lead-acid batteries, the weight is 1/3 of the lead-acid batteries.
7, 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 a key national support and encourage the development of the project. With China's accession to the WTO, China's exports of electric bicycles will rapidly increase, and into Europe and the United States electric bicycles have been required to be equipped with non-polluting batteries.
The disadvantages of lithium iron phosphate batteries
Whether a material has the potential for application development, in addition to focus on its advantages, more critical is whether the material has fundamental flaws.
Domestic now generally choose lithium iron phosphate as the cathode material for power lithium-ion batteries, from the government, research institutions, enterprises and even securities companies and other market analysts are optimistic about this material, as the direction of development of power lithium-ion batteries. Analysis of the reasons for the following two main points: First, the influence of the U.S. research and development direction, the U.S. Valence and A123 companies were the first to use lithium iron phosphate as the cathode material for lithium-ion batteries. The second is that the domestic has not been prepared for power lithium-ion batteries with good high-temperature cycle and storage performance of lithium manganate materials. But lithium iron phosphate also has fundamental defects that can not be ignored, boiled down to the following points.
1, in the preparation of lithium iron phosphate sintering process, iron oxide in a high-temperature reducing atmosphere there is the possibility of being reduced to singlet iron. Monolithic iron will cause a micro-short circuit in the battery, is the most taboo substance in the battery. This is the main reason why Japan has not been the material as a power-type lithium-ion battery cathode material.
2, lithium iron phosphate has a number of performance defects, such as vibration density and compaction density is very low, resulting in a low energy density of lithium-ion batteries. Poor low-temperature performance, even if it is nanosized and carbon cladding does not solve this problem. Dr. DonHillebrand, director of the Center for Energy Storage Systems at Argonne National Laboratory, talked about the low-temperature performance of lithium-iron phosphate batteries, he used terrible to describe their lithium-iron phosphate-type lithium-ion battery test results show that lithium iron phosphate batteries at low temperatures (below 0 ℃) can not make electric vehicles. Although some manufacturers claim that lithium iron phosphate battery capacity retention at low temperatures is not bad, but that is in the case of low discharge current and discharge cut-off voltage is very low. In this condition, the device simply can not start working.
3, the cost of material preparation and manufacturing costs of the battery is high, the battery yield is low and consistency is poor. Nanosized lithium iron phosphate and carbon cladding, despite the improved electrochemical performance of the material, but also brings other problems, such as the reduction of energy density, increased synthesis costs, poor electrode processing performance and harsh environmental requirements. Although the chemical elements in lithium iron phosphate Li, Fe and P are abundant, and the cost is low, but the cost of preparing lithium iron phosphate products is not low, even if you remove the preliminary research and development costs, the process cost of the material plus the higher cost of preparing the battery, will make the final unit of energy storage power cost is higher.
4, poor product consistency. There is no domestic lithium iron phosphate materials factory can solve this problem. From the point of view of material preparation, lithium iron phosphate synthesis reaction is a complex multiphase reaction, there are solid phase phosphate, iron oxides and lithium salts, plus carbon precursors as well as the reducing gas phase. In this complex reaction process, it is difficult to ensure the consistency of the reaction.
5, intellectual property issues. Currently the basic patent for lithium iron phosphate is owned by the University of Texas, while the patent for carbon cladding is applied for by the Canadians. These two basic patents can not be bypassed, if the cost of the patent royalties, then the product cost will be further increased.
In addition, from the experience of developing and producing lithium-ion batteries, Japan is the first country to commercialize lithium-ion batteries, and has been occupying the high-end lithium-ion battery market. And although the United States is leading in some basic research, there is not a large lithium-ion battery production enterprise so far. Therefore, Japan's choice of modified lithium manganate as a power-type lithium-ion battery cathode material is more justified. Even in the United States, the use of lithium iron phosphate and lithium manganate as a power-type lithium-ion battery cathode material manufacturers are also half of each, the federal government is also supporting the research and development of these two systems. In view of the above-mentioned problems of lithium iron phosphate, it is difficult to be widely used as the cathode material for power-type lithium-ion batteries in new energy vehicles and other fields. If the problems of high temperature cycling and poor storage performance of lithium manganate can be solved, there will be great potential for its application in power-type lithium-ion batteries with its advantages of low cost and high multiplier performance.
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