Ethylene Carbonate-diethyl Research Articles

Chemical properties of various organic electrolytes for lithium rechargeable batteries: 1. Characterization of passivating layer formed on graphite in alkyl carbonate solutions

The characteristics and reaction mechanisms of the passivating film formed on the surface of graphite were investigated in ethylene carbonate-diethyl carbonate solutions containing LiClO 4, LiPF 6 and LiN(SO 2CF 3) 2. The electron consumption resulting on the irreversible capacity of graphite was almost equivalent to that used in the one-electron reduction of Li + found in the film. The electrochemical reactions in the first discharge process may be divided into the following steps: (i) ‘initial film formation step’ from 1.4 to 0.55 V; (ii) ‘main film formation step’ from 0.55 to 0.2 V, and (iii) 'lithium intercalation step from 0.2 to 0.0 V. Most of the passivating film is formed together with the lithium intercalation reaction at step (ii). The passivating film formed at this step contained a significant amount of organic film such as EtOCO 2Li, (CH 2OCO 2Li) 2, etc. Through the consecutive formation of passivating film at steps (i) and (ii), lithium intercalation into graphite proceeds smoothly without further decomposition of the organic electrolyte.

Electrochemical behavior of an advanced graphite whisker anodic electrode for lithium-ion rechargeable batteries

Graphite whiskers, produced by Nikkiso Co., Ltd., (sample code 2GWH-2A) have been investigated with respect to their electrochemical characteristics in different types of liquid electrolytes: LiClO 4, LiPF 6, LiAsF 6, LiBF 4, LiCF 3SO 3 in ethylene carbonate-diethyl carbonate and in solid electrolytes. A high capacity (363 mAh/g) is obtained when a liquid electrolyte was used and 330 mAh/g at 80 °C in the case of a polymer electrolyte. The coulombic efficiency during the first cycle is lower when polymer electrolyte is used. 2GWH-2A shows very different performances in LiClO 4 and in LiPF 6 electrolytes. The degree of intercalation depends upon of the nature of the binder, composition of the electrode and electrolyte. The color of the carbon electrode also changed from black to gold in the presence of some lithium salt electrolytes, when lithium was fully intercalated into the electrode. The galvanostatic charge/discharge tests show a large plateau near 0 V. On measuring the slow cyclic voltammogram of the 2GWH-2A, five cathodic peaks were observed.