Local Crystal Structure around Manganese in New Potassium-Based Nanocrystalline Manganese Oxyiodide

Abstract

A new nanocrystalline potassium-based lithium manganese oxyiodide has been prepared by using Chimie Douce route at room temperature. According to the electrochemical measurements, this nanocrystalline sample shows a large initial capacity up to ∼340 mAh/g at a constant current density of 0.2 mA/cm 2 , which is much larger than that of sodium-based homologue. The X-ray diffraction analysis demonstrates that the amorphous character of the nanocrystalline compounds is maintained before and after chemical lithiation reaction. The local crystal structure around manganese in these materials has been determined by performing the combinative micro-Raman and X-ray absorption spectroscopy. From the Mn K-edge X-ray absorption near-edge structure and micro-Raman results, it becomes certain that manganese ions are stabilized in the rhombohedral layered lattice consisting of edge-shared MnO 6 octahedra, and the crystal symmetry is changed into a monoclinic symmetry upon reaction with n-BuLi. The Mn K-edge extended X-ray fine structure analysis reveals that the structural distortion caused by lithiation process is less significant for these nanocrystalline compounds than for the spinel lithium manganate. In this context, the great discharge capacity of the nanocrystalline materials is attributable for the pillaring effect of larger alkali metal ion than lithium ion, providing an expanded interlayer space available for Li insertion. In addition, the I L I -edge X-ray absorption near-edge structure results presented here make it clear that iodine is stabilized as iodate species on the grain boundary or the surface of the nanocrystalline manganese oxyiodide, which helps to maintain the nanocrystalline nature of the present materials before and after Li insertion.

Environmental Pollution, Causes and Consequences

“…According to chemical physics science [2][3][4][5][6][7], this assertion is a serious mistake intentionally or not. Anyway it's a great sin before public opinion of mankind.…”

A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

“…[ 6,7 ] A great deal of research effort has been devoted to the synthesis, characterization, and application of low-dimensional, nanostructured manganese oxides. [7][8][9][10][11][12] Generally, manganese oxide nanocrystals can be synthesized by soft-chemical reactions at low temperature in which the particle size of the manganese oxide is effectively regulated to the nanometer level. [ 8,9 ] Such a low-temperature reaction frequently produces amorphous or poorly crystalline materials, which is not advantageous for many functionalities of manganese oxide.…”

“…[7][8][9][10][11][12] Generally, manganese oxide nanocrystals can be synthesized by soft-chemical reactions at low temperature in which the particle size of the manganese oxide is effectively regulated to the nanometer level. [ 8,9 ] Such a low-temperature reaction frequently produces amorphous or poorly crystalline materials, which is not advantageous for many functionalities of manganese oxide. [ 8,9 ] The crystallinity of metal oxides can be easily improved by heat-treatment at elevated temperature.…”

“…[ 8,9 ] Such a low-temperature reaction frequently produces amorphous or poorly crystalline materials, which is not advantageous for many functionalities of manganese oxide. [ 8,9 ] The crystallinity of metal oxides can be easily improved by heat-treatment at elevated temperature. However, during heat-treatment at high temperature, the crystal size of metal oxides tends to increase through the agglomeration and fusion of small crystals, leading to the loss of the nanocrystalline nature.…”

New nanocrystalline manganese oxides as cathode materials for lithium batteries: Electron microscopy, electrochemical and X-ray absorption studies

“…XAS allows to probe the local environment of an absorbing element (here manganese) and to follow the variation of its environment and oxidation state with lithium insertion. It has been recently used in the study of nanometric or amorphous manganese oxides by several groups [23][24][25][26].…”