Nickel/sulfur composite electroplated nickel foams for the use as 3D cathode in lithium/sulfur batteries – A proof of concept

In this work, a composite electroplating method of manufacturing organic binder and conductive carbon free electrode materials is applied on nickel foam substrates, used as 3D current collector. Thereby, sulfur particles (d50 = 24 µm) are functionalized with polythiophene (layer thickness 100–200 nm) and brought to the surface of the nickel foam by means of composite electroplating while using nickel as a mechanically stable and electrically well conducting binding matrix for sulfur (Ni layer thickness around the sulfur particles < 1 µm). Therefore, organic nonconducting binders such as PVDF and conducting additives such as carbon are redundant. The method of composite electroplating ensures high sulfur loading with additional surface structuring, while keeping all pores accessible to the battery electrolyte. The naturally high surface of the metal foam is thereby further increased, which helps to decrease local current densities in the battery application. Cross-section SEM micrographs and CT images show that the functionalized sulfur particles are uniformly and densely distributed throughout the nickel foam. A battery capacity of about 300 mA h g−1sulfur over 100 cycles at a current density of 1 mA cm−2 (0.167 C) for a cathode containing 3.57 mg cm−2 sulfur is achieved. With an additional 50 nm thin NiSx alloy coating, the utilization of sulfur is improved by 250–300% (a battery capacity of about 800 mA h g−1sulfur over 100 cycles at a current density of 1 mA cm−2 (0.162 C) for a cathode containing 3.68 mg cm−2 sulfur is achieved). Furthermore, a high reversibility and rate capability is found when cycled between 0.1 and 1 C, respectively. A stable coulombic efficiency of about 100% is achieved.