Effect of electric fields on the thermal decomposition of solids

Zingel, E.M.

doi:10.1016/0040-6031(92)85073-5

Cited by 1 publication

(1 citation statement)

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“…Once again, the possible influence of a electromagnetic field on thermal decomposition temperatures and mechanisms add further uncertainty. 47 Assuming oxygen levels similar to air in the crucible, together with the absence of a visible glow in the CuO, one may speculate that the maximum peak temperature reached in the crucible was in the region of 500ЊC, although the presence of ␥-MnOOH in the IR spectra would suggest that such temperatures could not have endured for a long period. one would expect that this was due to absorbed water and/or water of crystallization.…”

Section: Resultsmentioning

confidence: 99%

Microwave Synthesis of Li[sub 1.025]Mn[sub 1.975]O[sub 4] and Li[sub 1+x]Mn[sub 2−x]O[sub 4−y]F[sub y] (x = 0.05, 0.15; y = 0.05, 0.1)

Whitfield

Davidson

2000

J. Electrochem. Soc.

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Rechargeable lithium-ion batteries are becoming increasingly important as power sources for a multitude of portable consumer electronics. Currently the material of choice for the cathode material is LiCoO 2 , which although having good capacity and rechargeability, suffers from the high cost and environmental toxicity of cobalt. Consequently, much effort has been put into developing alternatives. At present, the materials most likely to succeed in future commercial applications are LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , and related substituted systems. 1 Manganese-based compounds are particularly attractive due to the low cost and toxicity of manganese, so a wide range of compounds of that element has been studied. 2 LiMn 2 O 4 spinel in particular came to prominence in the early 1980s after it was demonstrated that lithium ions could be reversibly intercalated into LiMn 2 O 4 . 3,4 The material exhibits a two-stage charge/discharge at 3 and 4 V vs. Li, yielding a theoretical capacity of 296 mAh/g. However, it suffered from a number of practical problems, many of which have been overcome in the intervening years. The most troubling was the spinel's lack of long-term cyclability, shown by a marked fade in discharge capacity with cycle number. 2 This was attributed to a number of factors, including manganese dissolution, 5 electrolyte decomposition, 5 and microstructural fatigue brought about by a Jahn-Teller induced cubic-tetragonal transition. 2 Limiting the cycling to the 4 V plateau reduced but did not eliminate this structural distortion, as well as reducing the available theoretical capacity to 148 mAh/g. Substitution of some of the manganese for another element, e.g., excess Li, keeps the manganese oxidation state above 3.5 during cycling over the 4 V plateau, thus eliminating the Jahn-Teller distortion on discharge. This, together with an improved understanding of materials synthesis and processing, 6,7 has led to the achievement of good room-temperature cyclability with substituted spinel. However, its poor cyclability at elevated temperatures typically found in laptop computers, electric vehicles, etc., is an obstacle to its widespread introduction as a commercial cathode material. This mode of failure has been associated with accelerated manganese dissolution and formation of a protonated -MnO 2 phase, 8 and efforts to combat the problem have resorted to more exotic techniques than simple cation substitution.Fluorination as a means to change the structure and electronic properties of oxides became an established technique in the field of high-temperature cuprate superconductors. 9 Fluorine's ability to stabilize metastable structures made it a natural substituent in the quest for improved high-temperature storage and cycling of the lithium manganese spinels. [10][11][12] An alternative approach is the use of a barrier layer on the spinel particles to prevent contact with the nonaqueous electrolyte. 13 To date, much progress has been made, but further improvements in the elevated temperature performance of spin...

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Section: Resultsmentioning

confidence: 99%