Insertion lithium alloys

As to anodes, in most of the research work a generously dimensioned sheet of lithium metal has been used. Such an electrode is rather irreversible, but this is not noticed when a large excess of lithium is employed. Li-Al alloys and carbon materials inserting lithium cathodically during recharging can be used as anodes in nonaqueous solutions. Zinc has been used in polymer batteries with aqueous electrolyte (on the basis of polyaniline). 

When the halogen in the precursor is exceptionally mobile as an anion, even chloro compounds may give poor yields due to extensive self-destruction. For example, chloromethyl methyl ether can be expediently converted into methoxymethyllithium only if sodium/lithium alloy is used and a carefully elaborated protocol is meticulously followed . In the case of 7-chloronorbomadiene, the lithium/4,4 -di-ferf-butylbiphenyl radical anion has to be employed to further reduce the contact time between 7-norbornadienyllithium and its labile precursor. Many reductive metal insertions into... 

Lithium insertion negative electrodes — (i) Some transition-metal oxides or chalcogenides insert Li ion reversibly at low redox potentials, for example, TiC>2, LL I iOy, M0S2, M0O2. (ii) Lithium alloys - in this case lithium ions, react with other elements polarized to low potentials to reversibly form Li alloys. The reaction usually proceeds reversibly according to the... 

Higher OCV values can be attained with lithium alloys (Figure 16), which are under study as negative insertion electrode materials for their high specific capacity... 

Observations based on the alloy-type mechanism have shown that the reversible capacity of composite Sn oxides fades with cycling. In contrast, with the ionic-type mechanism, only slow capacity fading was observed with cycling. Using Li NMR (with LiCl solution as a reference), it was shown that the ionic nature of the inserted lithium is more than that for other negative electrode materials (Table 8.1). This indicates that ionic-type mechanisms may be possible. 

In the meantime, it was demonstrated that lithium can be reversibly inserted into graphite at room temperature in an organic electrolyte in 1983. Lithium-ion battery was first commercialized with this carbon-based anode in 1991. Graphite bas a capacity of 372 mAh/g, corresponding to the intercalation of one lithium atom per six carbon atoms. Though carbon bas ratber lower capacity than lithium metal and lithium alloy anodes, volume change was small and represented longer cycle performance. After this commercialization, many researchers and companies have put their effort on new carbonaceous anodes. 

From a thermodynamic point of view, apart from charge density and specific charge, the redox potential of lithium insertion into/removal from the electrode materials has to be considered also. For instance, the redox potential of many Li alloys is between -0.3 and -1.0 V vs. Li/Li+, whereas it is only -0.1 V vs. 

ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion [353]. Therefore, it may be an interesting network modifier for tin oxides. Also, ZnSnOs was proposed as a new anode material for lithium-ion batteries [354]. It was prepared as the amorphous product by pyrolysis of ZnSn(OH)6. The reversible capacity of the ZnSn03 electrode was found to be more than 0.8 Ah/g. Zhao and Cao [356] studied antimony-zinc alloy as a potential material for such batteries. Also, zinc-graphite composite was investigated [357] as a candidate for an electrode in lithium-ion batteries. Zinc parhcles were deposited mainly onto graphite surfaces. Also, zinc-polyaniline batteries were developed [358]. The authors examined the parameters that affect the life cycle of such batteries. They found that Zn passivahon is the main factor of the life cycle of zinc-polyaniline batteries. In recent times [359], zinc-poly(anihne-co-o-aminophenol) rechargeable battery was also studied. Other types of batteries based on zinc were of some interest [360]. 

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