(49d) Passivated Lithium Anodes of Lithium Sulfur Batteries with Modified Electrolyte Containing Transition Metal Acetate

One of the major challenges of Li-sulfur battery is long-term stability which can be due to dendrite formation and decomposition products on lithium metal anode. Herein, we propose a facile method to stabilize lithium anode surface in lithium sulfur batteries by incorporating transition metal acetate as electrolyte additives. A series of transition metal (zinc, copper, cobalt, nickel and manganese) acetates as electrolyte additives was investigated for their effectiveness in forming passivation layers. The most effective additive was found to be zinc acetate, showing an initial energy capacity of 950 mAh g^-1 and moderate decay to 855 mAh g^-1 after 100 cycles under 0.1 C, representing an average decay rate of 0.1%. However, the control sample without any electrolyte additive exhibited a rapid decay from 910 to 650 mAh g^-1 with an average decay rate of 0.27%.

Characterization of surface morphology of anodes before and after cycling revealed the effect of additives on promoting a smoother passivation layer with higher mechanical stability. This may be attributed to the fact that the passivation layer, mainly composed of transition metal sulfide, lithium sulfide and electrolyte decomposition product, could act as a physical barrier to suppress the lithium metal from dendrite formation, and continuously parasitic reactions with electrolyte and diffused polysulfides. In fact, XRD spectra indicated that the typical peaks of transition metal sulfide on lithium surface after 50 cycles.