Using the first-principles method within the density functional theory and the generalized gradient approximation, the properties of lithium deintercalation were studied in the ternary lithium transition metal nitride Li2.5Cu0.5N. The lithium deintercalation formation energies per lithium atom were found to be between −2.72 and −4.08eV for various amounts of Li extraction. The changes in the crystal volume, the electronic structures and the changes in charge densities of the Li x Cu0.5N due to Li extractions are also presented. This study demonstrates that the extraction of lithium ions from the [Li2N] layer is easier than that from the [Li0.5Cu0.5] layer. The change in unit cell volume was less than 5% for extractions of less than 30% of the Li ions in the unit cell. However, for a higher percentage of Li extractions, the system could shrink much more remarkably. The sequence of Li deintercalation, which was based on the calculated formation energies and the ratio of volume change, also gave some insight into the amorphization phenomenon after the first charge.