<p>This study presents the development and characterization of a novel spinel/layered heterostructured cathode material designed for enhanced energy storage capacity of lithium-ion batteries. The investigation began with the synthesis of Li-rich layered (Li_1.2Mn_0.5Ni_0.2Co_0.1O₂) and spinel (Li₄Mn₅O₁₂₎ cathode materials via a modified sol–gel method. These materials were then integrated to create heterostructured cathodes with compositions of xLi₄Mn₅O₁₂·(1-x)Li_1.2Mn_0.5Ni_0.2Co_0.1O₂ (x = 0.01, 0.03, 0.05, and 0.07). Comprehensive structural characterization using X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HR-TEM) confirmed the successful formation of the spinel/layered heterostructure. X-ray photoelectron spectroscopy validated the presence of the Li₄Mn₅O₁₂ spinel structure within the heterostructure matrix and verified the valence states of transition metal ions. The electrochemical performance of the Li-rich layered and heterostructure cathode materials was assessed through various measurements, including galvanostatic charge–discharge at different C rates, cyclic voltammetry, differential capacity, and electrochemical impedance spectroscopy. Electrochemical performance evaluation revealed that the optimized composition (x = 0.01) exhibited superior performance metrics, delivering specific capacities of 299.38, 231.48, 205.03, 174.93, and 115.67 mAh g⁻¹ at rates of 0.1C, 0.5C, 1C, 2C, and 5C, respectively. Notably, this composition maintained a stable capacity of 175.3 mAh g⁻¹ after 100 cycles at 1C rate, representing a 76.89% capacity retention. The enhanced performance is attributed to the synergistic effect of the ultrathin spinel layer, which facilitates Li-ion diffusion kinetics while protecting the layered structure from electrolyte degradation.</p>