Spinel LiMn₂O₄ is a promising cathode material for Li-ion batteries, but suffers from capacity fading, which can be mitigated. To this end, we developed a straightforward and cost-effective two-step synthesis strategy for high-phase-purity and crystalline spinel LiMn₂O₄ nanopowder; the precursor Mn₂O₃ was fabricated via a thermal decomposition reaction, followed by a solid-state reaction with lithium acetate dihydrate. Morphological investigation revealed the presence of nanosized octahedral particles of LiMn₂O₄, consistent with outcomes obtained via the established sol-gel method. The subsequent annealing process was elucidated; it led to the formation of pure crystalline spinel LiMn₂O₄ with a crystallite size of only 62.08 nm. The nanopowder synthesized via the two-step process exhibited exceptional cycling performance, with a substantial initial charge/discharge capacity of 136.6/133.3 mAh/g and an 81 % capacity retention after 100 charge–discharge cycles. Notably, the attained morphology closely mirrored those observed in particles prepared using the conventional sol-gel method and electrochemical results is remarkably improved. Therefore, the developed method is expected to have great potential for practical application in the development of Li-ion batteries as well as other energy storage technologies.