Spinel LiMn2O4 is an inexpensive, eco-friendly and highly abundant cathode material for lithium ion batteries. Here, we report a synthesis of nanoporous LiMn2O4 cathode material using a simple vacuum induced self-assembly reaction. Ammonia molecules play a key role in the formation of the nanoporous structure in our method. The galvanostatic charge/discharge results show that the nanoporous LiMn2O4 delivers a high specific capacity at high power rates. About 95.9% of its initial capacity (94.5 mAh g-1) is retained after 100 cycles at 10 C. The enhanced kinetics of nanoporous LiMn2O4 with low apparent activation energies indicates that the nanoporous structure provides short Li-ion diffusion paths and a continuous three-dimensional network of pathways for the transport of Li-ions and electrons. These results reveal that the nanoporous spinel LiMn2O4 material is a promising cathode candidate for next generation of high-power lithium ion battery.