Lithium Iron Phosphate: One of Promising Power Lithium-ion Battery Cathode Materials   

By Walker Wu, CCR

Since their inception in the early 1990s, lithium-ion batteries have become a fast-growing class of secondary batteries, because of their high energy density, good cycle performance and good electricity retention capability. As a key part of lithium-ion batteries, cathode materials have always been a hot research field.
   Till now, a variety of compounds have been found to be used as lithium-ion battery cathode materials, such as LiCoO2, LiMn2O4, LiNiO2 and LiFePO4. Of them, LiCoO2 has been commercialized and widely used in mobile phones, notebook PC and many other portable electronic devices. But because of its poor thermal stability, high security risks, limited cobalt resources and high costs, LiCoO2 is now only used in small-sized lithium-ion batteries, greatly limiting its future development. LiNiO2 has a complicated production process, limiting its industrialization. LiMn2O4 has a low theoretical specific discharge capacity (148 mAh/g) and poor cycle stability. Especially under high temperature conditions, it has severe capacity fading. LiFePO4 (lithium iron phosphate) has abundant and cheap raw materials, being cheap, non-toxic and environmentally friendly, and having high theoretical specific discharge capacity (170 mAh/g) and a high discharge voltage (3.45V for Li / Li+). Because of these, it has become a very promising cathode material for power lithium-ion batteries for electric vehicles.
    Electric vehicles have been developing fast around the world. Thus, the global demand for power lithium-ion batteries is growing fast. Power lithium-ion batteries for electric vehicles should meet the following requirements: high discharge capacity, high discharge voltage, good charge-discharge cycle performance, good discharge voltage stability, good high-rate performances, good electrochemical stability, high safety performance (no fires or explosions occur due to overcharge, over discharge, short circuit and other improper operations), wide operating temperature range, no or little toxicity and environmental friendliness. Power lithium-ion batteries using LiFePO4 as the cathode material have good performances in these aspects, featuring good high-rate discharge performance (5 - 10C discharge), stable discharge voltage, good safety performance (no fires, no explosion), long cycle life and environmentally friendliness, etc.
   Now, LiFePO4 has been used in electric bicycles, electric motorcycles, electric golf carts, electric boats, electric vehicles, power tools, electric toys, lighting batteries and other energy storage devices.
   In China, there are dozens of LiFePO4 producers. Major producers are PULead Technology Industry Co Ltd, BYD, Hunan Reshine New Material Co Ltd, China BAK Battery Inc, and Tianjin Lishen Battery Co Ltd. They each have a LiFePO4 production capacity of 5 000 - 10 000 t/a.