Impurities in LiFePO4 and Their Influence on Material Characteristics

Li 3 PO 4 impurity was found in hydrothermally grown LiFePO 4 samples made with excess Li. The impurity dissociates in water, leading to an apparent alkaline nature of the LiFePO 4 sample. The impurity can be removed by washing the sample in a neutral buffer solution, after which an increase in specific capacity of the LiFePO 4 sample was observed. Li 3 PO 4 , as an inactive component within the active material, reduces the energy density of LiFePO 4 . Additional experiments were performed to study the reactivity of LiFePO 4 in different environments. It is found that LiFePO 4 decomposes in a strong alkaline solution and the decomposition can be slowed down by carbon coating the material. After prolonged storage in water, the specific capacity of carbon-coated LiFePO 4 is reduced and Fe dissolution is observed. Material degradation is thought to be due to interactions among LiFePO 4 , impurities, and water.