The First Intercalation Step in Carbonaceous Anodes

The first 1.5 charge-discharge cycles of lithium/carbon cells are presented in Fig. 4 for both graphite (b) and petroleum coke (a) [71], In both cases, the first intercalation capacity is larger than the first deintercalation capacity. 

This difference is the irreversible capacity loss ( 2jr). Dahn and co-workers [71] were the first to correlate 21R with the capacity required for the formation of the SE1. They found that 2ir is proportional to the specific surface area of the carbon electrode and, assuming the fonnation of an Li2C03 film, calculated an SEI thickness of 45 5 A on the carbon particles, consistent with the barrier thickness needed to prevent electron tunneling [1,2]. They concluded [71] that when all the available surface area is coated with a film of the decomposition products, further decomposition ceases. 

In general, lithium-ion batteries are assembled in the discharged state. That is, the cathode, for example LqCoC, is filly intercalated by lithium, while the anode (carbon) is completely empty (not charged by lithium). In the first charge the anode is polarized in the negative direction (electrons are inserted into the carbon) and lithium cations leave the cathode, enter the solution, and are inserted into the carbon anode. This first charge process is very complex. On the basis of many reports it is presented schematically [6, 74, 76] in Fig. 5. The reactions presented in Fig. 5 are also discussed in Sec. 6.2.1, 6.2.2 and 6.3.5. 

At the electrode surface there is competition among many reduction reactions, the rates of which depend on iQ and overpotential q for each process. Both /0 and q depend on the concentration of the electroactive materials (and on the catalytic properties of the carbon surface). However, the chemical composition of the SEI is also influenced by the solubility of the reduction products. As a result, the voltage at 

Reference v E, (V) r (Lmol 1 s ) Material Carbon type Electrolyte 

Reference VsEi (V) fceNlmoM s-1] 1 Material Carbon type Electrolyte 

Bar-Tow, C. and Menachem, E. Peled, (unpublished results) 1.2 9 X 10 AsFe Graphite fibers LiAsFe/EC-DEC 

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