High voltage spinels are of great interest as positive electrode materials for lithium-ion batteries in recent years due to the increasing market of electric vehicles. In this study, a new organic solvent system is explored for preparing this composite material via a co-precipitation process. The use of a functional polymer surfactant significantly affects both the structure and stoichiometry of the spinel compounds in the non-aqueous batch reaction. It was revealed that the residual halides and impurities can be completely eliminated at the precursor stage. A good cycling stability was demonstrated at room temperature and a greatly improved rate capability was successfully derived from this novel system as compared with the traditional aqueous system. The superior rate performance is mainly attributed to the appreciable formation of trivalent Mn, correlating with the change of Ni/Mn ordering and crystallographic phase transformation in the detailed structural analysis.