LiMBO3 (M=Mn, Fe, Co):: synthesis, crystal structure and lithium deinsertion/insertion properties

The LiMBO3 (M=Mn, Fe, Co) compounds were synthesized by a solid state reaction. LiFeBO3 and h-LiMnBO3 crystal structures were determined from single crystal data. LiFeBO3 exhibits the same structure as that of other already described LiMBO3 compounds (M=Mg, Mn, Co, Zn). The structure of h-LiMnBO3 is isotypic with the hexagonal form of LiCdBO3. The electrochemical study shows that a very small amount of lithium (less than 0.04 Li per formula unit) can be deinserted reversibly from the three compounds. According to the thermodynamic study performed in the case of LiFeBO3, the Fe3+/Fe2+ redox couple lies between 3.1 and 2.9 V/Li, demonstrating an important inductive effect of the BO3 group.