The nanoscale 0.5Li2MnO3·0.5Li(Ni0.44Mn0.44Co0.12)O2 Li-manganese-rich electrode material was synthesized by the co-precipitate method, and its electrochemical properties were systematically analyzed, especially the electrochemical impedance spectroscopy. The failure of the electrode interface and the structural transformation of the material at high potential are the main reasons for the deterioration of the Li-manganese-rich electrode, and high temperatures accelerate the deterioration. Based on the systematic analysis of the induced reactance change with electrode polarization potential, it is found that the induced reactance of a Li-manganese-rich electrode is not only related to the degree of delithiation/lithiation but also has a great relationship with the performance of the electrode/electrolyte interface. This conclusion is beneficial for the manufacturing of battery failure analysis by providing a theoretical basis for guidance.