锂硫二次电池正极研究进展

综述了锂硫电池中硫基正极材料的制备方法、结构特征以及电化学性能. 简述了单质硫正极材料, 重点探讨了有机硫化物、碳/硫复合材料、聚合物/硫复合材料的结构设计、材料制备、反应机理以及充放电特性, 并对其中存在的问题进行了分析, 还介绍了硫化锂正极材料. 最后对硫基正极的进一步发展, 以及锂硫电池的商业化应用进行了展望.     

Graphs to chemical structures 1. Sphericity indices of cycles for stereochemical extension of Pólya’s theorem

Pólyas theorem has been concluded to be concerned with graphs, but not with chemical structures, where it is incapable of treating chiral ligands properly. In order to take account of chiral ligands along with achiral ones, coset representations (CRs) for cyclic subgroups have been examined to classify permutations of the CRs into proper and improper elements. As a result, a k-cycle contained in each permutation has been classified into an enantiospheric, homospheric, or hemispheric one. Thereby, sphericity indices of k-cycles have been defined according to the enantiospheric, homospheric, or hemispheric nature of each k-cycle. On the basis of the sphericity indices, cycle indices with chirality fittingness (CIs-CF) have been defined in place of Pólyas cycle indices. The CIs-CF have been proved to be capable of enumerating of stereoisomers with chiral and achiral ligands. Their capabilities have been confirmed by using allene derivatives as examples.