Phase Transformation of Gamma‐EMD to Beta Manganese Dioxide during Digestion in Sulfuric Acid

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.

Section: X-rays Mn02mentioning

confidence: 85%

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

Larcher

Courjal

Urbina

et al. 1998

“…The solid was then separated, washed, dried, and analyzed using XRD. The concentration of barium metalplumbate after soak was calculated from the XRD pattern based on the "degree of resemblance," a technique reported in the literature (21,22). The XRD peak of BaPbO3 used for this purpose corresponds to the diffraction from the (110) plane with a d spacing about 3.00 A.…”

Section: Methodsmentioning

confidence: 99%

A Conductive Additive to Enhance Formation of a Lead/Acid Battery

Kao

Bullock

1992

Barium metaplumbate, a conductive ceramic having the perovskite structure, is relatively stable in sulfuric acid. Addition of this material in positive plates in a lead/acid battery significantly improves formation efficiency. The formation mechanism is changed when the conductive particles are dispersed in the plate. Formation not only proceeds from the grid toward the center of the pellet but also slowly around the conductive particles in the plate. The conductive paths of PbO2 grow and make connection with each other during formation to establish a network which further facilitates the formation.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.119.168.112 Downloaded on 2014-10-01 to IP

“…Because of its low electrochemical activity in dry cells, the beta-phase material is an undesirable product in the EMD processes. The description of the formation of this beta-phase material in EMD or the transformation of ~-EMD to ~-MnO2 under the conditions similar to that for the EMD preparation can be found in the literature (1)(2)(3)(4)(5)(6). However, the kinetics of this phase transformation, denoted as betafication hereafter in the text, is still not well understood.…”

mentioning

confidence: 99%

“…Some other authors suggested that the oxidation or disproportionation of MnOOH on partially reduced or hydrated MnO2 surfaces would lead to the formation of ~-MnO2 (7,8). In the presence of Mn 2 § in the acidic electrolyte, betafication occurred at a temperature lower than the boiling point of the electrolyte (3)(4)(5)(6). Under dry conditions, in contrast, one had to raise the temperature of ~-EMD beyond 300~ before betafication could be observed (9,10).…”

mentioning

confidence: 99%

“…From this laboratory we reported (3,4) the rate of betafication as a function of temperature, initial Mn 2 § concentration in the acidic electrolyte, and EMD particle size. The betafication was speculated to be initiated by the equilibration between EMD and Mn 2+ in the electrolyte to yield an intermediate Mn(III), either as MnOOH on the EMD surfaces or as free Mn 3 § ions…”

mentioning

confidence: 99%

See 1 more Smart Citation

The Role of the Acidic Electrolyte in the Phase Transformation of Gamma‐EMD to Beta‐Manganese Dioxide

Kao¹

1989

The influence of acidic strength of the manganous sulfate electrolyte on the nucleation and growth of ~-MnQ in the gamma-phase electrolytic manganese dioxide (~]-EMD) is examined. It is found that the growth of ~-MnO2 in EMD is firstorder with respect to the bulk acid concentration. It is suggested that the reduction of EMD by Mn 2 § to generate Mn(III) intermediates initiates the phase transformation. The subsequent disproportionation of Mn(III) intermediates produces ~-MnQ. The growth of ~-MnO2 in EMD is controlled by the diffusion of hydrogen ions in the lattice of EMD and the redox of EMD and Mn 2 § ions in the electrolyte via a galvanic type cell through the semiconducting EMD.