Publications (2)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: The current-potential relationships for the electrochemical oxidation of organic solvent electrolytes on microelectrodes are confirmed for various lithium salts, namely ${\rm LiClO}_4$, ${\rm LiBF}_4$, ${\rm LiCF}_3{\rm SO}_3$ and ${\rm LiPF}_6$. The oxidation is expected to occur by means of a two stage process; the chemical degradation of the solvent followed by the electrochemical generation of anion radical species, and the direct electrochemical oxidation of the solvent. The dependence of the oxidation current on temperature and the lithium salt concentration confirms this two step reaction feature. In other words, a reaction based on electrochemically generated anion radicals seems to occur below 4.8V vs. Li/Li$^+$ and direct oxidation of the solvent occurs above 4.8V. Above 4.8V, we cannot disregard the distribution of the diffusion-limiting current of the anion radical into the whole oxidation current.
-
[show abstract]
[hide abstract]
ABSTRACT: The decomposition of LiPF$_6$ electrolytes with water was studied by measuring the water content after storage. The solvents used are ethylene carbonate (EC) + diethyl carbonate (DEC), EC + dimethyl carbonate (DMC), propylene carbonate (PC) + DEC and PC + DMC. The experimental results were in good agreement with $-d[{\rm H}_2{\rm O}]/dt = k [{\rm H}_2{\rm O}]^2 [{\rm LiPF}_6]$. We obtained rate constant (k) from this empirical equation and rate constant (k) increased in the order of EC+DMC < EC+DEC < PC+DMC < PC+DEC. This order is inverse proportion to order of dielectric constant of these solvents. Non-ionized LiPF$_6$ dissociates to PF$_5$ and LiF in organic solvents and PF$_5$ reacts with water. High dielectric constant solvent increases the ionization of LiPF$_6$. Therefore, the reaction with water is suppressed in high dielectric constant solvent.
