Propylene carbonate decomposition potentials

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

Baranski and Lu [209] have carried out, applying microelectrodes, voltammetric studies on ammonium amalgam in propylene carbonate solutions at room temperatures. The sweep rates up to 80 V s were appropriate for the analysis of the formation kinetics of this compound. Experimental and numerical simulation results have shown that ammonium amalgam was formed via fast charge-transfer process and its first-order decomposition was characterized by the rate constant of about 0.6 s . Diffusion coefficient of NH4 radical in mercury was estimated to be about 1.8 X 10 cm s k The formal potential of NH4+ (aq)/NH4(Hg) couple was determined as—1.723 V (SHE). 

Other solvents that have high anodic decomposition potentials (above 2.5 V vs see) are nitromethane, nitroethane, propylene carbonate, sulfolane, dichloromethane/ methanesulfonic acid or trifluoromethanesulfonic acid " . Except for the latter two " there are no reports on their use as solvents for alkane oxidation. 

Ab initio calculation methods predicted that the current solvents for the electrolytes used in Li-ion batteries often have oxidation stability to 5.5 V vs. Li" /Li (propylene carbonate, ethylene carbonate, dimethyl carbonate). In practice, the potential limits are far below as illustrated by the work of Kanamura et For instance, the stability of PC-based electrolyte varied from 5 V (calculation) to 4.2 V vs. Li" /Li (experiment). The origin of this difference may be multiple "catalytic effect of the insertion materials, traces of water in the electrochemical system, influence of Li salts. In some cases, the decomposition of the electrolyte is accompanied by the formation of a solid film on the surface of the positive electrode. ... 

The fact that Schrock s proposed metallocyclobutanes decomposed to propylene derivatives rather than cyclopropanes was fortunate in that further information resulted regarding the stereochemistry of the olefin reaction with the carbene carbon, as now the /3-carbon from the metal-locycle precursor retained its identity. The reaction course was consistent with nucleophilic attack of the carbene carbon on the complexed olefin, despite potential steric hindrance from the bulky carbene. Decomposition via pathways f-h in Eq. (26) was clearly confirmed in studies utilizing deuterated olefins (67). 

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