Whether a material has application and development potential depends not only on its advantages, but also on its fundamental defects. At present, lithium ferrous phosphate is widely selected as the cathode material of power lithium ion batteries in China. Market analysts such as 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: first, influenced by the research and development direction of the United States, Valence and A 123 companies in the United States took the lead in adopting lithium iron phosphate as the cathode material of lithium ion batteries. Secondly, lithium manganate materials with good high-temperature cycling and storage performance for power lithium-ion batteries have not been prepared in China. However, lithium ferrous phosphate also has some fundamental defects that cannot be ignored, which can be summarized as: 1. In the sintering process of preparing lithium ferrous phosphate, iron oxide will be reduced to elemental iron in high temperature reducing atmosphere. Elemental iron can cause micro-short circuit of battery, which is the most taboo substance in battery. This is also the main reason why Japan has not used this material as a cathode material for power lithium-ion batteries. 2. Lithium ferrous phosphate has some performance defects, such as low tap density and compaction density, which leads to low energy density of lithium ion batteries. Poor low temperature performance, even if nano-sized, carbon-coated, this problem has not been solved. Dr. DonHillebrand, director of the Energy Storage System Center of Argonne National Laboratory in the United States, described the low-temperature performance of lithium iron phosphate batteries as terrible. Their test results of lithium iron phosphate lithium ion batteries show that lithium iron phosphate batteries cannot drive electric vehicles at low temperatures (below 0℃). Although some manufacturers claim that the capacity retention rate of lithium iron phosphate battery is good at low temperature, this is under the condition of small discharge current and low discharge cut-off voltage. In this case, the equipment can't start working at all. 3. The preparation cost of this material is higher than that of the battery, and the battery yield is low and the consistency is poor. Although nano-LiFePO4 and carbon coating improve the electrochemical properties of the materials, they also bring other problems, such as decreased energy density, increased synthesis cost, poor electrode processability and harsh environmental requirements. Although the chemical elements Li, Fe and P in lithium ferrous phosphate are rich and cheap, the cost of the prepared lithium ferrous phosphate product is not low. Even if the previous research and development costs are removed, the process cost of materials and the higher cost of preparing batteries will make the final unit energy storage cost higher. 4. Poor product consistency. At present, there is no lithium ferrous phosphate material factory in China that can solve this problem. From the point of view of material preparation, the synthesis of lithium ferrous phosphate is a complex multiphase reaction, including solid phosphate, iron oxide and lithium salt, carbon precursor and reducing gas phase. In this complicated reaction process, it is difficult to ensure the consistency of the reaction.
5. Intellectual property rights. The earliest patent application for lithium ferrous phosphate was filed by Fxmittermeier &: SOEHNEOHG(DE) on June 25th, 1993, and the application result was announced on August 9th, 1993. The basic patent of lithium ferrous phosphate is from the University of Texas, while the patent of carbon coating is applied by Canadians. These two basic patents cannot be bypassed. If royalties are included in the cost, the product cost will further increase.
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 always occupied the high-end lithium-ion battery market. Although the United States leads in some basic research, there is no large-scale lithium-ion battery manufacturer so far. Therefore, it is more reasonable for Japan to choose modified lithium manganate as the cathode material of power lithium ion battery. Even in the United States, lithium ferrous phosphate and lithium manganate are also used as cathode materials for power lithium-ion batteries, and the federal government also supports the research and development of these two systems. In view of the above problems, lithium ferrous phosphate is difficult to be widely used as a cathode material for power lithium-ion batteries in new energy vehicles and other fields. If the problems of poor high-temperature cycle and storage performance of lithium manganate can be solved, it will have great potential in the application of power lithium-ion batteries with its advantages of low cost and high rate performance.
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