Synthesis of MnO2 Phases from LiMn2 O 4 in Aqueous Acidic Media: Mechanisms of Phase Transformations, Reactivity, and Effect of Bi Species

Abstract

The nature of the phases obtained by acid digestion of LiMn2O4 phases prepared at 800°C from a mixture of Mn02 (EMD) and Li2CO3 was investigated. We found that the complete transformation toward a-Mn02 and then -y-Mn02 observed for LiMn2O, treated in 2.5 M H2S04 for 24 h at 05°C is highly dependent on the amount of water in the reaction medium. The ) -. u/-y transformation was found to be the result of a dissolution.-crystallization mechanism that can be completely avoided by adding a soluble Ri, Pb, or TI salt to the reaction medium. By coupling energy dispersive spectroscopy analysis, infrared spectroscopy, and potentiometric titration, we demonstrated the presence of Bi species adsorbed at the surface of the X-MnO, oxide thus modifying its reactivity. In addition, the kinetics of the X -°u/-y phase transformation was found to depend on the amount of added Bi salt, suggesting the complexing role of Bi toward Mn (Ri-Mn complexes), thereby affecting the crystallization step of the reaction. The same treatment was applied to LiMn,04 in the presence of a Bi salt in anhydrous electrolyte (LiPF6/ethylene carbonate/dimethyl carbonate). In this case, the spinel oxide dissolution slows down and Ru1 precipitates. With respect to recent findings about the mechanisms involved in the electrochemical capacity failure at elevated temperature in Li-ion LiMn2O4 cells, these results open new alternatives to solve this recurrent problem.

Structure Investigation and Electrochemical Behavior of γ-MnO2 Synthesized from Three-Dimensional Framework and Layered Structures

“…The discharge capacity of CMD 2D was close to that of CMD 3D (0.87 and 0.90 electron/formula unit, e À / fu, respectively) but it was higher than that of MOL85Ti (0.79 e À /fu). This agrees with the observation of Larcher et al (17) who stated that it is not attributed to the different water content. It may be attributed to the fact that MOL85Ti has pyrolusite faults, P r ¼ 0:37 (25) (which cannot be reduced at the given pH through proton diffusion mechanism (24)) more than CMD 2D and CMD 3D , P r ¼ 0:16 and 0.20, respectively (Table 2).…”

Electrochemical Behavior of Electrolytic Manganese Dioxide in Aqueous KOH and LiOH Solutions: A Comparative Study

“…• C, 22,23,24 and the product was separated from solution by centrifugation and rinsed with water. An unidentified crystalline impurity was present in the initial product, but could be removed by washing with alkaline aqueous solution.…”

“…2b) is in agreement with that reported in previous work. 23,24 The (210), (211), (212), and (402) peaks were used in calculating the lattice parameters for the R-MnO 2 since these are expected to be unaffected by De Wolff disorder. 10 The γ-and R-MnO 2 were characterized (Table I) in terms of degree of microtwinning (Tw) and level of De Wolff disorder (P r , the pyrolusite fraction) using the method of Chabre and Pannetier, which is based upon simulated diffraction patterns for model structures.…”

α‐MnO2 Nanowires: A Catalyst for the O2 Electrode in Rechargeable Lithium Batteries

“…All other MnO 2 catalysts-bulk and nanowire a-MnO 2 , nanowire b-MnO 2 , bulk g-MnO 2 , and bulk l-MnO 2 -were prepared according to literature procedures. [11][12][13][14][15] Powder X-ray diffraction data were collected for all the catalysts on a STOE STADI/P diffractometer operating with Fe Ka1 radiation (l = 1.936 ). Surface areas were determined by N 2 adsorption/ desorption (Micrometrics ASAP2020), and morphologies were examined by SEM (JEOL JSM-5600 and FEI quanta 200F) and TEM (JEOL 2010).…”