机械活化-湿化学合成LiMn_2O_4的组成、结构与表征

Characterization, structure and performances of LiMn_2O_4 synthesized by mechanically activated-wet chemistry

以MnO2和LiOH·H2O为原料,采用机械活化与湿化学集成的方法,在水溶液中直接合成了结晶态的尖晶石锂锰氧化物。当锂含量介于3.78%～4.35%之间时,所得锂锰氧化物为纳米级球形粉末,以尖晶石结构为主,含极少量的Mn3O4杂相;在300～800℃温度范围内热处理后,Mn3O4杂相消失,尖晶石结构更趋完善。所合成的含锂5.80%的高锂样品则以LiMnO2层状结构为主,含少量Mn3O4杂相,其SEM形貌为片状;在300～700℃下热处理8h后,层状LiMnO2转变成尖晶石LiMn2O4,Mn3O4杂相峰明显减弱并随热处理温度的升高而消失;当温度升高至700～800℃时,开始出现缺锂的Li1-xMn2O4相。结果表明:该法制备锂锰氧化物可实现锂、锰、氧在原子级水平的均匀混合,所得产物的热稳定性能良好,其化学计量组成与结构易于调整和控制。

A crystal spinel LiMn_2O_4 was directly synthesized by using MnO_2 and LiOH·H_2O as raw materials in aqueous solution by the process of wet-chemistry integrated with mechanically activation. The synthesized Li-Mn-O compound with Li content between 3.78%4.35% is a nano-powerder with mainly spinel structure of LiMn_2O_4 besides a little impurity Mn_3O_4 and similar spherical morphology. After being heat treated at 300800 ℃ for 8 h, a single spinel LiMn_2O_4 with perfect structure was obtained with the disappearing of Mn_3O_4 phase. The sample with Li content of 5.80% has a mainly layered structure of LiMnO_2 besides some Mn_3O_4 and lamellar morphology. The layered LiMnO_2 can be transformed completely into spinel LiMn_2O_4 after being heat treated at 300700 ℃ and the Mn_3O_4 phase decreased gradually and disappeared at last, but a little Li_(1-x)Mn_2O_4 was formed above 700 ℃. The results show that Li, Mn and O can be mixed in atomic level to form spinel LiMn_2O_4 in the present process. The products synthesized with Li less than 4.35% have a good thermal stability and the chemical composition and phase structure can be easily adjusted and controlled.