Reversible capacity, origins

DBMS) [ARM 06] nevertheless, the quantity of gas detected was not sufficient to compensate for the total quantity of lithium deintercalated on the plateau . It has been shown that this unusual mechanism arose due to the reversible participation of the oxygen anion in the redox processes. This original mechanism, demonstrated for the first time for layered oxides, is possible due to the particular composition of these Li- and Mn-rich materials the hybridization of transition metals nd levels and anions 2p levels leads to a mixed redox process involving both the cations and the anions [KOG 13a, SAT 13a, SAT 13b]. This mechanism, responsible for the exceptional reversible capacity these materials deliver, is enhanced for transition metals that are highly oxidized and electronegative (Figure 2.13). 

The encapsulations of organic molecules, like 9,10-dichloro-anthracene, jS-carotene, and coronene was found to be effective to increase the reversible storage capacity. Especially for the SWNT with coronene, the reversible capacity is 736 mAh/g, which is about 2.5 times greater than that of original empty tube. This is due to the steric hindrance of the organic molecules in the tube. The electrol3 e molecules and solvated Li ions cannot enter the tube. 

Disproportionation of Olefins. Disproportionation or the metathesis reaction offers an opportunity to convert surplus olefins to other desirable olefins. Phillips Petroleum and Institut Fransais du Petrc le have pioneered this technology for the dimerization of light olefins. The original metathesis reaction of Phillips Petroleum was intended to convert propylene to 2-butene and ethylene (58). The reverse reaction that converts 2-butene in the presence of excess ethylene to propylene has also been demonstrated (59). A commercial unit with a capacity of about 136,000 t/yr of propylene from ethylene via 2-butene has been in operation in the Gulf Coast since 1985 (60,61). In this process, ethylene is first dimerized to 2-butene foUowed by metathesis to yield propylene. Since this is a two-stage process, 2-butene can be produced from the first stage, if needed. In the dimerization step, about 95% purity of 2-butene is achieved at 90% ethylene conversion. 

Relaxation methods for the study of fast electrode processes are recent developments but their origin, except in the case of faradaic rectification, can be traced to older work. The other relaxation methods are subject to errors related directly or indirectly to the internal resistance of the cell and the double-layer capacity of the test electrode. These errors tend to increase as the reaction becomes more and more reversible. None of these methods is suitable for the accurate determination of rate constants larger than 1.0 cm/s. Such errors are eliminated with faradaic rectification, because this method takes advantage of complete linearity of cell resistance and the slight nonlinearity of double-layer capacity. The potentialities of the faradaic rectification method for measurement of rate constants of the order of 10 cm/s are well recognized, and it is hoped that by suitably developing the technique for measurement at frequencies above 20 MHz, it should be possible to measure rate constants even of the order of 100 cm/s. 

Figure 5. Comparison of the reversible and irreversible capacities of the original and ground B-doped carbon from WUT.

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