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why LiFePO4 battery is not common use on ebike and ebike kits?

why LiFePO4 battery is not common use on ebike and ebike kits?

  • Saturday, 05 August 2017
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Lithium iron phosphate battery eight advantages and shortcomings

Lithium iron phosphate battery, refers to the use of lithium iron phosphate as a cathode material lithium-ion battery. Lithium-ion battery cathode materials are mainly lithium cobalt oxide, lithium manganese oxide, lithium nickelate, ternary materials, lithium iron phosphate and so on. Lithium cobalt oxide which is currently the vast majority of lithium-ion battery using the cathode material.

Eight advantages

Improved safety performance

The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose, and it does not have the same structure as the lithium cobalt oxide, or it forms a strong oxidizing substance even at high temperature or overcharge. It has been reported that a small part of the sample is found to have a burning phenomenon in the acupuncture or short circuit experiment, but there is no case of explosion, and the overcharge test uses a high voltage charge that is much higher than its own discharge voltage. Explosion phenomenon. Even so, its overcharge safety than ordinary liquid electrolyte lithium cobalt oxide battery, has been greatly improved.

Improved life expectancy

Lithium iron phosphate batteries refer to lithium ion batteries using lithium iron phosphate as the cathode material.

Long life lead-acid battery cycle life of about 300 times, the highest will be 500 times, while the lithium iron phosphate battery, the cycle life of more than 2000 times, the standard charge (5 hours rate) use, up to 2000 times. The same quality lead-acid battery is the "new half year, the old half year, maintenance and maintenance of six months", up to 1 ~ 1.5 years, and lithium iron phosphate batteries in the same conditions, the theoretical life will reach 7 to 8 years. Considering, the performance-cost ratio is more than four times theoretically for lead-acid batteries.

Can be a large current rapid discharge

Large current discharge can be high current 2C fast charge and discharge, in a dedicated charger, 1.5C charge 40 minutes to make the battery is full, starting current up to 2C, and lead-acid batteries without this performance.

High temperature performance is good

The peak value of lithium iron phosphate can reach 350 ℃ -500 ℃ and lithium manganese oxide and lithium cobalt oxide only about 200 ℃. Wide operating temperature range (-20C - +75), high temperature characteristics of lithium iron phosphate heating peak up to 350 ℃ -500 ℃ and lithium manganese oxide and lithium cobalt oxide only about 200 ℃.

High capacity

Has a larger capacity than ordinary batteries (lead acid, etc.). 5AH-1000AH (monomer)

No memory effect

Rechargeable batteries are often in the conditions of full of spare conditions, the capacity will quickly lower than the rated capacity value, this phenomenon is called the memory effect. Like nickel-metal hydride, nickel-cadmium battery memory, and lithium iron phosphate battery without this phenomenon, regardless of what state the battery can be charged with the use, no need to put the first re-charge.

Light weight

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

Environmental protection

The battery is generally considered to be free of any heavy metal and rare metal (nickel-metal hydride batteries to be rare metal), non-toxic (SGS certified), non-polluting, in line with European RoHS requirements for absolute green battery card. So the reason why the lithium battery is optimistic about the industry, mainly environmental considerations, so the battery was included in the "15" during the "863" national high-tech development plan, a national key support and encourage the development of the project. With China's accession to the WTO, China's electric bicycle exports will increase rapidly, and enter the European and American electric bicycles have been equipped with non-polluting batteries.

Disadvantages

Whether a material has application development potential, in addition to its advantages, the more critical is whether the material has a fundamental flaw.

China is now widely selected lithium iron phosphate as a dynamic lithium-ion battery cathode material, from the government, research institutions, enterprises and even securities companies and other market analysts are optimistic about this material, as a dynamic lithium-ion battery development. Analysis of the reasons, mainly the following two points: First, by the direction of the US R & D, the United States Valence and A123 company first use lithium iron phosphate lithium battery as a cathode material. Followed by the domestic has not prepared for the use of power-type lithium-ion battery with good high temperature cycle and storage performance of lithium manganese oxide material. But there is also a lithium iron phosphate can not be ignored fundamental defects, summed up mainly in the following points:

1. In the sintering process when lithium iron phosphate is prepared, the presence of iron oxide in the high-temperature reducing atmosphere is reduced to the possibility of being reduced to elemental iron. Elemental iron will cause the battery short circuit, is the most taboo material in the battery. This is also Japan has not the material as a power lithium-ion battery cathode material the main reason.

2, lithium iron phosphate there are some performance defects, such as tap density and compaction density is very low, resulting in lithium ion battery energy density is low. Low temperature performance is poor, even if its nano-carbon and carbon coating did not solve this problem. Dr. Don Hillebrand, Director of Energy Storage Systems Center, Argonne National Laboratory, said that when he spoke of low-temperature performance of lithium iron phosphate batteries, he used terrible to describe their lithium iron lithium ion battery test results showed that lithium iron phosphate battery at low temperature (0 ℃ below) can not make electric vehicles driving. Although there are manufacturers claim that lithium iron phosphate battery capacity at low temperatures is not bad, but it is in the discharge current is small and the discharge cut-off voltage is very low case. In this situation, the device simply can not start work.

3, the cost of preparation of materials and battery manufacturing costs higher, low battery yield, poor consistency. The nanocrystallization and carbon coating of lithium iron phosphate, while improving the electrochemical properties of the material, also bring other problems such as lower energy density, improved synthesis cost, poor electrode processing performance and harsh environmental requirements. Although the chemical elements in lithium iron phosphate Li, Fe and P is very rich, the cost is low, but the preparation of lithium iron phosphate product cost is not low, even if the early removal of the cost of research and development, the material cost of the process with a higher The cost of preparing the battery will make the final unit of the higher cost of energy storage.

4, product consistency is poor. At present, there is not a lithium iron phosphate plant can solve this problem. From the point of view of material preparation, the synthesis reaction of lithium iron phosphate is a complex multiphase reaction with solid-phase phosphates, iron oxides and lithium salts, plus carbon precursors and reducing gas phase. In this complex reaction process, it is difficult to ensure the consistency of the reaction.

5, intellectual property issues. The earliest patent application for lithium iron phosphate was obtained by F X MITTERMAIER & SOEHNE OHG (DE) on June 25, 1993 and published on August 19 of the same year. The basic patent for lithium iron phosphate is owned by the University of Texas, and the carbon-coated patent is filed by Canadians. These two basic patents can not be bypassed, if the cost of the calculation of royalties on the use of the product cost will be further improved.

In addition, from the experience of R & D and production of lithium-ion battery, Japan is the first commercial lithium-ion battery country, and has occupied the high-end lithium-ion battery market. While the United States despite some basic research on the lead, but so far there is no large-scale lithium-ion battery manufacturers. Therefore, Japan chose to change the lithium manganese oxide as a dynamic lithium-ion battery cathode material more reason. Even in the United States, the use of lithium iron phosphate and lithium manganese oxide as a power lithium-ion battery cathode material manufacturers are also half of the federal government is also supporting the development of these two systems. In view of the existence of lithium iron phosphate of the above problems, it is difficult as a dynamic lithium-ion battery cathode materials in the field of new energy vehicles and other widely used. If you can solve the problem of high temperature cycle and storage performance of lithium manganate, with its low cost and high magnification performance advantages, in the application of power lithium-ion battery will have great potential.

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