Optimization and Fabrication of Binder-Free Nickel-Copper Phosphate Battery-type Electrode Using Microwave-Assisted Hydrothermal Method

In this study, a binder-free nickel-copper phosphate battery-type electrode was fabricated using a microwave-assisted hydrothermal technique. The fabrication process was optimized with Design of Experiment (DoE) software and then validated experimentally. The electrode made at 90 °C for 12.5 min, with a Ni:Cu precursor ratio of 3:1, had the highest specific capacity. The experimental specific capacity of the optimized nickel-copper phosphate (Ni3-Cu-P) binder-free electrode was 96.2% of the theoretical value predicted by the software, which was within 10% error. Moreover, the growth of amorphous Ni3-Cu-P electrode material with irregular microspheres of small size was observed on the surface of nickel foam. These amorphous microspherical shapes of the Ni3-Cu-P electrode material provide more electroactive sites and a larger active surface area for faradaic reaction. In electrochemical energy storage applications, the Ni3-Cu-P electrode outperformed the bare Ni-P and Cu-P electrodes, with the highest areal capacity (0.77 C cm⁻²), the lowest charge transfer resistance (81.7 Ω), and the highest capacity retention (83.9%) at 2.0 mA cm⁻². The study indicates that the Ni3-Cu-P electrode’s exceptional electrochemical properties result from the interaction between nickel and copper in the binary metal phosphate framework, making it an excellent choice for battery-type electrodes used in electrochemical energy storage applications.