Whether a material has potential for application development, in addition to focusing on its advantages, is more critical whether the material has fundamental defects.
Lithium iron phosphate is widely used as a positive electrode material for power lithium-ion batteries in China. Market analysts such as government, scientific research institutions, enterprises and even securities companies are optimistic about this material as the development direction of power lithium-ion batteries. Analysis of the reasons, mainly have the following two points: First, the impact of the US research and development direction, the United States Valence and A123 company first used lithium iron phosphate as the cathode material for lithium-ion batteries. Secondly, there has been no preparation of lithium manganate materials with good high temperature cycle and storage properties for use in power lithium-ion batteries. However, lithium iron phosphate also has fundamental defects that cannot be ignored. The main points are as follows:
1. During the sintering process in the preparation of lithium iron phosphate, iron oxide is likely to be reduced to elemental iron under a high temperature reducing atmosphere. Elemental iron can cause micro short circuit of the battery, which is the most taboo substance in the battery. This is also the main reason why Japan has not used this material as a positive electrode material for a lithium-ion battery.
2. There are some performance defects in lithium iron phosphate, such as low tap density and compaction density, resulting in low energy density of lithium ion batteries. Low temperature performance is poor, even if it is nano-sized and carbon coated, this problem is not solved. Dr. Don Hillebrand, director of the Center for Energy Storage Systems at Argonne National Laboratory, spoke about the low-temperature performance of lithium iron phosphate batteries. He used terrible to describe that their test results for lithium iron phosphate-type lithium-ion batteries indicate that lithium iron phosphate batteries are at low temperatures. Under (below 0 °C), electric vehicles cannot be driven. Although some manufacturers claim that the lithium iron phosphate battery has a good capacity retention rate at low temperatures, it is in the case of a small discharge current and a low discharge cut-off voltage. In this situation, the device simply cannot start working.
3. The preparation cost of the material and the manufacturing cost of the battery are high, the battery yield is low, and the consistency is poor. The nanocrystallization and carbon coating of lithium iron phosphate, while improving the electrochemical performance of the material, also brings other problems such as a decrease in energy density, an increase in synthesis cost, poor electrode processing performance, and environmentally demanding problems. Although the chemical elements Li, Fe and P in lithium iron phosphate are abundant and the cost is low, the cost of the prepared lithium iron phosphate product is not low, even if the previous research and development cost is removed, the process cost of the material is higher. The cost of preparing the battery will make the cost of the final unit of stored energy higher.
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