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New materials have been sought for battery cathodes for lithium-ion batteries and supercapacitors due to their shorter charging times, faster electron resorption, and high potential capacities. The development of single crystals is essential to analyze intrinsic properties of a material since they eliminate contributions from extrinsic factors such as impurities and grain boundaries. Here we present a method to grow high quality Li₂Mn₂(MoO₄)₃ single crystals from molten oxide solution. In-situ x-ray diffraction measurements allowed us to optimize the crystal growth of this material and avoid the formation of an undesired intermediary compound. These results show a way to accelerate the discovery and synthesis of new battery cathode materials.