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Keywords:

  • Copper;
  • Sulfur;
  • Cluster compounds;
  • Structure elucidation;
  • Electrochemistry

Abstract

Two different approaches were developed for the synthesis of lithiated copper(I) sulfide with the formal composition “Li2Cu4S3”. In the first approach, thiolato-bridged copper cluster complexes [Li(dme)3]2[Cu4(SPh)6] (dme = dimethoxyethane) and [Li(diglyme)2]2[Cu4(SPh)6] (diglyme = diethylene glycol dimethyl ether) were decomposed/thermolized at 400 °C to form the lithiated copper(I) sulfides upon cleavage of the ether ligands and 3 equiv. of SPh2. In the second approach, Li2S and 2 equiv. of Cu2S were allowed to react in quartz ampoules sealed under vacuum at 400 °C. The as-synthesized powders reveal complex room-temperature XRD powder patterns with clear differences between the two materials. Scanning electron microscopy reveals that the material synthesized by thermolysis of the cluster material is composed of a porous network of agglomerated nanoparticles, whereas the other material is composed of compact micron-sized crystals. The initial specific capacities for galvanostatic charging and discharging of nanostructured and porous “Li2Cu4S3” cathodes vs. lithium metal anodes in a limited range between 1.7 and 3 V are ca. 143 A h kg–1. This is 97.3 % of the theoretical value for the exchange of two lithium ions and 5 % higher than for the compact material at ca. 136 A h kg–1. However, we observed that upon prolonged cycling the capacity of the nanostructured and porous “Li2Cu4S3” fades much faster than that of the compact material. This means that after 100 cycles the nanostructured and porous material had faded by 67 %, whereas the compact material still reaches a specific capacity of 109 A h kg–1.