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-type lithium-ion batteries. However, lithium iron phosphate also has fundamental defects that cannot be ignored. It comes down to the following points:
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, it does not solve this problem. 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 their lithium iron phosphate battery test results indicating that lithium iron phosphate battery is at low temperature. (Below 0 °C) It is not possible to drive an electric car. 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.
4. Poor product consistency. At present, there is no domestic lithium iron phosphate material factory that can solve this problem. From the viewpoint of material preparation, the synthesis reaction of lithium iron phosphate is a complex heterogeneous reaction, which has solid phase phosphate, iron oxide and lithium salt, a carbon precursor and a reducing gas phase. In this complex reaction process, it is difficult to ensure the consistency of the reaction.
5. Intellectual property issues. At present, the basic patent for lithium iron phosphate is owned by the University of Texas, and the carbon coated patent is applied by Canadians. These two basic patents cannot be circumvented. If the cost of the patent is calculated, the cost of the product will be further increased.
In addition, from the experience of research and development and production of lithium-ion batteries, Japan is the first commercialized country of lithium-ion batteries, and has always occupied the high-end lithium-ion battery market. Although the United States is leading in some basic research, there is still no large-scale lithium-ion battery manufacturer. Therefore, Japan has chosen modified lithium manganate as the positive electrode material for power lithium-ion batteries. Even in the United States, lithium iron phosphate and lithium manganate are used as the cathode materials for power-based lithium-ion batteries, and the federal government also supports the development of these two systems. In view of the above problems of lithium iron phosphate, it is difficult to be widely used as a positive electrode material for a power lithium ion battery in fields such as new energy vehicles. If it can solve the problem of high temperature cycle and poor storage performance of lithium manganate, with its advantages of low cost and high rate performance, it will have great potential in the application of power lithium-ion batteries.
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