<p>In this work, doped spinels LiNi_0.05Mn_1.95O₄ and LiLa_0.05Mn_1.95O₄, as well as pure LiMn₂O₄, were successfully obtained by a citrate synthesis method and investigated as cathode materials for lithium-ion batteries with aprotic and aqueous electrolytes. It has been shown that due to the closeness of the ionic radius to Mn³⁺, nickel ions easily incorporate into the spinel structure, increasing its stability. In contrast, lanthanum ions, due to their large size, do not integrate into the structure but form a separate LaMnO₃ phase on the spinel surface, enhancing charge transfer and kinetics. In an aprotic system, LiNi_0.05Mn_1.95O₄ and LiLa_0.05Mn_1.95O₄ showed excellent capacity retention of 92.7 and 83.1%, respectively, after 200 cycles, compared to 69.8% for pure LiMn₂O₄. At high discharge rates (up to 50 C), the doped samples exhibited improved rate performance, attributed to enhanced structural stability and transport properties. In an aqueous system, all samples exhibited poorer cycling stability but superior rate capability (with capacity retention up to 92% at 50 C) compared to aprotic systems. In contrast to the aprotic system, where the LiNi_0.05Mn_1.95O₄ sample showed slightly better performance, the LiLa_0.05Mn_1.95O₄ sample exhibited the highest cyclic stability in the aqueous system, indicating in this case a greater effectiveness of the LaMnO₃ surface layer formation. The calculated values of the lithium diffusion coefficient for the spinel samples confirmed the improved kinetics and charge transfer in the aqueous system, due to the higher electrical conductivity of the aqueous electrolyte and the lack of a solid electrolyte interface characteristic of aprotic systems.</p> Graphical abstract <p></p>