Dimensionally stable LiCoMnO4 having a spinel-framework structure was developed as a positive electrode of lithium-ion batteries with a long cycle life. Well-crystallized LiCoMnO4 prepared by a two-step solid-state reaction shows large rechargeable capacity of 120 mAh g−1 at high operating voltage of 5 V. Ex-situ XRD measurements of the LiCoMnO4 revealed small change in the cubic lattice parameter (ca. 0.7%) during charge and discharge. Change in electrode thickness of LiCoMnO4 measured by using a precision dilatometer is accordance with the change in the cubic lattice parameter. The LiCoMnO4 electrode showed high dimensional stability compared with other LiMn2O4-based materials having a spinel-framework structure.