The air-exposed Li2FeSiO4 was characterized and regenerated by calcination under argon. The original Li2FeSiO4 was prepared by a sol–gel method and was then exposed in air for a year. The impact of long-term air exposure on the structure, surface and electrochemical characteristics of Li2FeSiO4 was investigated. In comparison with the original sample, the air-exposed sample was seriously oxidized. The oxidation speed decreases with increasing air-exposure time. The oxidization of Li2FeSiO4 led to surface change and deteriorated electrochemical performance. However, the changes induced by air exposure were entirely reversible. The one year air-exposed Li2FeSiO4 was regenerated by calcination under Argon. The regeneration conditions including calcination temperature and calcination time were optimized. The sample regenerated by calcining at 700°C for 4h had similar structure, surface and electrochemical characteristics to the original sample. Based on detailed analysis, the possible regeneration mechanisms were proposed.