Enhanced structural and electrochemical stability in Ni-Co substituted lithium ferrites for energy storage devices

Nickel and cobalt co-substituted lithium ferrites, Li 0.5- x Ni x Co x Fe 2.5- x O 4 (with x = 0.0, 0.1, 0.3 and 0.5), were synthesized via a sol–gel auto-combustion route to examine their potential for energy-storage applications. X-ray diffraction confirmed a structural evolution from a single-phase cubic P4 1 32 lattice at x = 0.0 to a spinel Fd-3 m structure with increasing Ni–Co content, indicating cation redistribution within the lattice. SEM micrographs revealed a reduction in average particle size from 140 nm to 123 nm and agglomerated spherical morphologies that enhance interparticle contact. EDX analysis verified elemental uniformity and stoichiometric precision. Magnetic characterization showed progressive increases in saturation magnetization and coercivity with higher Ni–Co substitution, attributed to stronger superexchange coupling and increased magnetic anisotropy. FESEM images displayed a porous nanostructure resulting from gas release during combustion, which improves electrolyte penetration and charge transfer. Such porosity enhances the electrochemical response of the ferrite electrodes. Electrochemical analyses (CV, EIS, and GCD) demonstrated superior capacitive performance for the substituted compositions, exhibiting higher capacitance, lower impedance, and excellent rate capability. The materials retained about 30–40% of their initial capacitance after 10,000 cycles, confirming long-term stability. These findings highlight that Ni–Co-doped lithium ferrites combine tunable magnetic behavior with enhanced electrochemical performance, making them promising candidates for efficient supercapacitor and energy-storage systems.