************ The 20th Lab Seminar **************************************

Title : Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable 
Batteries Electrochemistry Branch, 
Sensor and Electron Devices Directorate, U.S. Army Research Laboratory, 
Adelphi, Maryland 20783-1197
(Chem. Rev. 2004,104,4303-4417)
6.2. Electrolyte/Carbonaceous Anode Interface:SEI

Speaker : Sakai Hirofumi

Date : Thu. Mar. 28th, 1:30 pm

Abstract:
6.2.1. Exfoliation and Irreversible Capacities on a Carbonaceous Anode
  It has been known since the mid 1950s that graphite can form inter-
calation compounds with lithium ions, which are accommodated in the 
interstitial region between the planar graphene sheets. The most lithium-
enriched intercalation compound of this family has a stoichiometry of 
LiC6, and its chemical reactivity is very similar to that of lithium metal.

6.2.2. Mechanism of SEI Formation
  According to Peled's model, the existence of an SEI constitutes the 
foundation on which lithium ion chemistry could operate reversibly. 
Therefore, an ideal SEI should meet the following requirements:
(1) electron transference number te ) 0 (otherwise, electron tunneling 
would occur and enable continuous electrolyte decomposition), (2) high 
ion conductivity so that lithium ions can readily migrate to intercalate 
into or deintercalate from graphene layers, (3) uniform morphology and 
chemical composition for homogeneouscurrent distribution, (4) good 
adhesion to the carbonaceous anode surface, (5) good mechanical strength 
and flexibility so that it allows the expansion and contraction of the 
graphene lattice during the reversible intercalation/deintercalation 
process, and (6) low solubility in electrolytes so that continuous 
dissolution of SEI would not occur, resulting in persistent decomposition 
of electrolyte and consummation of the limited source of lithium from the 
cathode.

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