The co-doping with metal cations and incorporation of the Li₇La₃Zr₂O₁₂ (LLZO) superionic conductor into spinel LiNi_0.5Mn_1.5O₄ are achieved in situ through a spray drying method by co-doping with Zr and La elements. Microscopic structural characterizations reveal that the doping of hetero-cations into LiNi_0.5Mn_1.5O₄ is effective at reducing the amount of Mn³⁺, enhancing the cation ordering, and improving the structural stability of LNMO crystals. Scanning transmission electron microscopy (STEM) and Energy Dispersive Spectrometric (EDS) analyses validate the successful growth of LLZO during the calcination of the LNMO material. Incorporation of the LLZO superionic conductor into the bulk phase of LNMO considerably improves the intrinsic lithium diffusion rate within the crystal. Electrochemical studies reveal that the LNMO/LLZO composite at 50 : 1 ratio exhibits the best overall electrochemical behavior, in terms of reversible capacity, rate capability, and long-term cycling performance. At 20C discharge rate, the composite cathode delivers a capacity of 84.5 mA h g⁻¹, whereas the pristine LNMO only maintains 14.8 mA h g⁻¹ capacity. After 300 cycles, a capacity retention of 95.9% is obtained for the composite electrode, but only 87.6% for the pure LNMO cathode. The lithium ion diffusion coefficient of 1.83 × 10⁻¹⁰ cm² s⁻¹ is obtained for the composite cathode, which is three times as high as that of pure LNMO (6.43 × 10⁻¹¹).