On the performance of a hierarchically porous Ag₂S-CuS electrode in Li-ion batteries

A new binder- and carbon-free electrode for lithium-ion batteries was prepared using a hierarchically porous Ag-based current collector. The latter was produced by applying the method of selective dissolution of the less noble metals from the Cu₆₀Ag₃₀Al₁₀ master alloy tape. The current collector was reaction-coated with an electrochemically active Ag₂S-CuS coating. The metallic structure provided a mechanically stable conductive scaffold on the walls of which the Ag₂S-CuS skin material was directly deposited. The ordered porosity - hierarchical and directional - provided easy penetration of the liquid electrolyte as well as short Li⁺ ion diffusion paths. The as-prepared electrodes were tested in a half-cell configuration vs. Li/Li⁺ at various current rates to study the cycling and rate performances of the electrode. The first cycling capacity of ∼1250 mA h g^-1 was measured at 0.4 A g^-1 current rate. After a rapid decrease, a stable reversible capacity of ∼230 mA h g^-1 was established at a current rate of 0.4 A g^-1 (calculated vs. the weight of the incorporated sulphur). Excellent charge/discharge cycling and rate properties were observed for over 1000 cycles at higher rates of 1.0 and 2.0 A g^-1, in the potential window of 0.15-2.8 V vs. Li/Li⁺. The observed cycling stability was ascribed to the mechanism of a "displacement" reaction with Li ions. Additional capacity is also available from alloying-dealloying with Ag (and Cu to some extent) and S redox reactions. These results open up a new opportunity for using a Cu-Ag alloy as the precursor for making electrodes for thin Li-ion and Li-S batteries with high cycling stability at relatively high current rates.