J. Gnanaraj, E. Zinigrad, L. Asraf
Nov 1, 2003
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Influential Citations
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Journal
Electrochemistry Communications
Abstract
Abstract Electrolyte solutions comprising a mixture of LiPF 6 and LiPF 3 (CF 2 CF 3 ) 3 (LiFAP) in alkyl carbonates (ethylene, dimethyl and diethyl carbonate) were found to be superior to single salt LiFAP or LiPF 6 solutions for lithium–graphite anodes at elevated temperatures. Graphite electrodes could be cycled (Li insertion–deinsertion) more than hundred times at 80 °C with high and stable capacity in the two-salt solutions, while in the single-salt solutions this was impossible. Preliminary studies by voltammetry and impedance spectroscopy indicate that the combination of the two salts in solution has a unique influence on the electrodes surface (not yet defined). Thermal studies by accelerating rate and differential scanning calorimetry show that thermal decomposition of LiFAP solutions has a higher onset, but very high heat and pressure developing rates, compared to LiPF 6 solutions. The presence of LiPF 6 in LiFAP solutions decreased their self-heating and pressure-developing rates pronouncedly. From product analysis of the thermal reactions by NMR, FTIR and MS, we can suggest possible unique bulk reactions that occur in LiPF 6 –LiFAP solutions. One of these is a nucleophilic reaction between F − and PF 3 (CF 2 CF 3 ) 3 − , which may neutralize the effect of trace HF in solutions (thus forming new P–F bonds and HCF 2 CF 3 ). Such a reaction should have a positive effect on both the performance of the Li–graphite electrodes and the thermal behavior of the solutions.