Design,preparation And Modification Research Of Lithium Iron Phosphate Cathode Materials With High Compacted Density

The increasingly severe energy crisis is one of the greatest challenges mankind faced in the 21st century.Developing environmentally friendly and sustainable energy storage route is vital to meet the increasing demand.Lithium-ion rechargeable battery is the most promising power system that can offer the higher operative voltage and energy density.Lithium iron phosphate is a kind of ideal cathode material for lithium ion power battery,because of its high capacity density,excellent cycling performance,stability and safety,environmental friendliness and low cost of raw materials.However,the low energy density is a problem that needs to be solved urgently.We use the following solutions to increase the compaction density of the battery.?1?LiFePO₄@C with high tap density 1.45 g cm^-3 was synthesized via ball-milling method and calcination using Li₃PO₄,FePO₄,Fe and glucose as raw materials.Comparing with other methods,it achieves nearly 100%utilization of raw materials and is easy to realize industrial production,and no other by-products are generated except for a small amount of gas decomposed from glucose.The raw materials are tightly bounded together,which is beneficial to the crystallization and easy to form dense lithium iron phosphate.The combination of theoretical research and industrialization can lead to the greatest economic benefits.?2?Lithium iron phosphate with olivine type crystal structure has good electrochemical and thermal stability,however,the one-dimensional lithium ion diffusion obstructs its rate performance.In this aspect,the LiFePO₄ with iron vacancies was designed and synthesized which allows lithium ions to transport to the adjacent diffusion channels through vacant iron sites and thus increase the lithium ion diffusion rate,thereby the high rate performance is improved.The specific capacity is 140mAh g^-1 with charge and discharge rate at 1C.?3?Compaction density is an important parameter in the manufacture of lithium-ion batteries which has a significant influence on the improvement of cycle performance and volumetric energy density,especially for poor conductivity materials such as lithium iron phosphate.Based on the investigation of compaction density,we find that the appropriate compaction density is positive to the battery's rate performance.Once the commonly used acetylene black is replaced by carbon nanotubes with high conductivity,the conductivity and the high-current charge/discharge capacity will be improved.In this work,the compaction density of the prepared electrode is 2.32 g cm^-3,which is higher than that of the contrast electrode(2.15 g cm^-3 prepared by commercial LiFePO₄@C).