Other Positive Electrode Materials

Metal sulfides (M-S) were first developed to replace elemental sulfur as the positive electrodes for higjh-temperature (above 400 °C) lithium-sulfur batteries [97]. A number of M-Ss (M = Fe, Co, Ni, etc.) are being investigated as positive 

The binder, an indispensable component, plays an important role in maintaining the structural integrity of the electrodes and thus the capacity and the cycleability of the lithium-sulfur batteries. A good binder should be able to form a good network between sulfur and conductive materials which is stable and facilitates the electronic and ionic transport [109]. 

PEO shows a fair ionic conductivity arising from its coordination with lithium ions [29]. By using PEO as binder in the cathode, 80% of theoretical capacity is delivered for the first discharge and a capacity of 100 mAh g is retained at 80 °C. The morphology and the electrochemical properties of the cathode depend on the processing procedure and the type of binder a mechanically stirred mixture of PEO, carbon, and sulfur forms a porous PEO film which has better cycleability than the ball-milled mixture, which forms a dense and thick layer of PEO over the sulfur particles. In contrast, when poly(butadiene-co-styrene) (PBS) is used as a binder the ball milled dry mixture has good cycleability [15]. In general, PEO shows poor adhesion properties [14, 21] and low ionic conductivity at low temperature [110], and electrodes made with it show better performance at elevated temperatures. 

The use of polytetrafluoroethylene (PTFE)-carboxymethyl cellulose (CMC) com-posits as the binder improves the capacity and sulfur utilization compared with polyvinylpyrrolidone (PVP) and composite PTFE-polyvinyl alcohol (PVA) binders [111], but no cycling performance has been reported. In another paper, capacity 

Additives such as methyl acetate (MA), toluene, and y-butyrolactone (GBL) have been studied for their effects on capacity and cycleabiUty [17, 129]. Only toluene improves both the initial capacity and cycleability owing to its capabiHty of forming a stable electrode/electrolyte interface [124, 129]. ImidazoHum salts, when introduced into the mixed DME-DOL electrolytes, are reported to improve the cycleability by enhancing the electrochemical reaction of polysulfides and improving the stability of the lithium negative electrode [122]. Addition of tetrabutylam-monium hexafluorophosphate (TBAPFg) into the electrolyte shows a comparable effect [113]. 

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As the cost of LiCo02 is high, other positive electrode materials will eventually take the place of LiCoOz. LiNiOz and... 

Poor performance at low temperature in comparison with other positive electrode materials such as LiCo02 and LiMn204. 

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