Abstract
MnO2 was chemically prepared from birnessite (CMD2D) and from spinel-like LiMn2O4 (CMD3D) by acid leaching. X-ray diffractometry, FTIR spectrometry, chemical and thermal analyses were used to determine the structure and chemical disorder. On the basis of cation vacancy model, the structural water was found to be mainly due to Coleman protons in both samples. Both samples were found to be of very close structure belonging to γ-MnO2 type I according to Chabre and Pannetier classification with de Wolff disorder (Pr) of 0.19 and 0.30 and microtwinning (Tw) of 9.9 and 17%, respectively. The activation energy of structural water release calculated from thermal analysis was apparently higher than that of other γ-MnO2 types (150 and 156.6 kJ/mol, respectively).A high reduction capacity in aqueous and non-aqueous batteries was delivered for both samples except for the electro- chemical lithium insertion of CMD2D, which was attributed to the different oxygen packing.
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