<p>The development of energy storage devices with high energy density, environmental compatibility, and cost-effectiveness requires strategies to overcome the intrinsic structural instabilities of LiMn₂O₄. In this work, a chemical doping approach based on aluminum metal diffusion via thermal annealing was investigated to suppress the Jahn–Teller distortion in LiMn₂O₄ thin-film cathodes. Cyclic voltammetry revealed the characteristic high-voltage redox couple of LiMn₂O₄ (3.9–4.2&#xa0;V vs. Li/Li⁺), but also displayed electrochemical activity in the lower voltage range (2.6–3.1&#xa0;V), indicative of a persistent Jahn–Teller distortion. Charge–discharge measurements yielded specific capacities (30 to 100 mAh g⁻¹) below the theoretical value of 148 mAh g⁻¹ and lower than the ~ 119 mAh g⁻¹ reported in previous studies. Electrochemical impedance spectroscopy showed lithium-ion diffusion coefficients in the range of 10⁻⁹–10⁻¹¹ cm²&#xa0;s⁻¹, consistent with typical LiMn₂O₄ values but without evidence of enhanced transport kinetics from aluminum diffusion. These results suggest that diffusion-driven doping via thermal annealing is insufficient to mitigate the Jahn–Teller effect in LiMn₂O₄, highlighting the need for alternative doping strategies.</p> Graphical abstract <p></p>