Highly cross-linked porous NiCo2S4 nanosheets arrays are synthesized by a high-efficiency hydrothermal conversion from the preformed electrodeposited NiCo2O4 arrays. By using thioacetamide as the sulfur source, the electrodeposited NiCo2O4 is directly converted into NiCo2S4 nanosheets arrays without high-temperature sulfurization. Higher porosity and better electrical conductivity are obtained for the NiCo2S4 nanosheets arrays. In addition, reduced diffusion paths of electrons/ions and alleviated volume expansion during cycling are achieved due to the unique porous structure of NiCo2S4. Consequently, as the cathode of alkaline batteries, the obtained NiCo2S4 nanosheets arrays show better electrochemical performance with a high specific capacity (83.5 mAh g−1 at 0.5 A g−1) and better cycling stability (capacity retention of 93% after 5000 cycles) than the NiCo2O4 counterpart arrays (40.3 mAh g−1 at 0.5 A g−1). Our work demonstrates that sulfurization on binary metal oxides can greatly enhance electrochemical performance and shows a new way for construction of advanced electrodes for high-rate batteries.