Mechanical processes such as ball milling trigger lattice deformations into particles. The electrochemical performances of the electrode materials used for Li-ion batteries depend on Li+ mobility within the crystal structure. Therefore, the preparation of electrode particles that contain no lattice deformations is required. However, electrode particles are subjected to mechanical stresses during manufacturing processes such as grinding, mixing, and coating of powders. In this study, the introduction of lattice strains and defects into the LiNi0.5Mn1.5O4 (LNMO) spinel by a simple ball-milling process is investigated, together with the relationship between lattice deformation and cathode properties. Lattice strain accumulates in the LNMO crystal with increased milling time, but the crystallite size of the distorted particles reduces in order to mitigate this effect. Although mechanical treatment leads to a decrease in the first discharge capacity, there is a recovery in capacity after the second discharge owing to crystal rearrangement that occurs after the initial extraction and insertion of Li+ from the distorted LNMO spinel. Nonetheless, excessive lattice deformation in the LNMO spinel, which contains a three-dimensional diffusion pathway for Li+, disturbs fast migration. The design and quality management of electrode particles throughout the manufacturing process are key factors for improving battery performances.