Disadvantages of lithium iron phosphate batteries

Whether a material has application development potential, in addition to focusing on its advantages, it is more critical whether the material has fundamental defects.
Lithium iron phosphate is now generally chosen as the positive electrode material of power lithium-ion batteries in China. Market analysts from the 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 to analyze the reasons: First, under the influence of the research and development direction of the United States, the American Valence and A123 companies were the first to use lithium iron phosphate as the positive electrode material for lithium-ion batteries. Secondly, there is no lithium manganate material with good high temperature cycle and storage performance that can be used in power lithium-ion batteries in China. However, lithium iron phosphate also has fundamental defects that cannot be ignored, which can be summed up as follows:
1. During the sintering process during the preparation of lithium iron phosphate, iron oxide may be reduced to elemental iron in a high-temperature reducing atmosphere. Elemental iron can cause micro-short circuit of the battery and 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 power lithium-ion batteries.
2. Lithium iron phosphate has some performance defects, such as low tap density and compaction density, resulting in low energy density of lithium-ion batteries. The low temperature performance is poor, and even nano-encapsulation and carbon coating did not solve this problem. When Dr. Don Hillebrand, director of the Energy Storage System Center of Argonne National Laboratory in the United States, talked about the low temperature performance of lithium iron phosphate batteries, he described it as terrible. It is not possible to drive an electric vehicle at low temperature (below 0°C). Although some manufacturers claim that the capacity retention rate of lithium iron phosphate batteries is good at low temperatures, that is when the discharge current is small and the discharge cut-off voltage is very low. In this condition, the device cannot start working at all.
3. The material preparation cost and the battery manufacturing cost are high, the battery yield is low, and the consistency is poor. Although the nanoscale and carbon coating of lithium iron phosphate improves the electrochemical performance of the material, it also brings other problems, such as the reduction of energy density, the increase of synthesis cost, poor electrode processing performance, and harsh environmental requirements. Although the chemical elements Li, Fe and P in lithium iron phosphate are very rich and the cost is low, the cost of the prepared lithium iron phosphate product is not low. Even if the early research and development costs are removed, the process cost of the material is relatively high. The cost of preparing the battery will make the final cost per unit of energy storage higher.
4. Poor product consistency. At present, there is no lithium iron phosphate material factory in China that can solve this problem. From the perspective of material preparation, the synthesis reaction of lithium iron phosphate is a complex heterogeneous reaction, including solid phase phosphate, iron oxide and lithium salt, plus carbon precursor 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 the application results were announced on August 19 of the same year. The basic patent of lithium iron phosphate is owned by the University of Texas, and the carbon coating patent is applied by Canadians. These two basic patents cannot be bypassed. If the patent royalty is included in the cost, the product cost will be further increased.
In addition, from the experience of R&D and production of lithium-ion batteries, Japan is the first country to commercialize lithium-ion batteries, and has been occupying the high-end lithium-ion battery market. Although the United States is leading in some basic research, so far there is no large-scale lithium-ion battery manufacturer. Therefore, it is more reasonable for Japan to choose modified lithium manganate as the positive electrode material of power lithium-ion battery. Even in the United States, the number of manufacturers using lithium iron phosphate and lithium manganate as cathode materials for power lithium-ion batteries is equally divided, and the federal government supports the research and development of these two systems at the same time. In view of the above problems of lithium iron phosphate, it is difficult to be widely used as a positive electrode material for power 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, with its advantages of low cost and high rate performance, the application in power lithium-ion batteries will have great potential.