Symmetric full cells attract much attention because of various advantages including almost no cell volume expansion, simplified fabrication and reduced costs. Li- and Mn-rich layered oxide (LMROs), the traditional high-capacity cathode material, demonstrates excellent reversible capacities as anode electrode in half cell and the reaction mechanism is comprised mainly of conversion reaction. Herein, for the first time, a novel symmetric lithium-ion full battery is systemically studied constructed with bi-functional Li- and Mn-rich layered oxide 0.3Li2MnO3·0.7LiNi1/3Co1/3Mn1/3O2 (LMROs//LMROs), not involving any prelithiated/predelithiated treatments. Benefited from the high specific capacity of LMROs as cathode and anode electrodes and the potential gap between two redox couples, this symmetric battery exhibits excellent electrochemical performance, with a satisfactory capacity of 150.6 mAh g−1, average voltage of 2.01 V and energy density of 306.4 Wh kg−1 at 30 mA g−1 between 0.05 and 3.6 V. The specific capacity is superior among all the previous reported symmetric energy storage systems (including symmetric lithium/sodium/potassium ion batteries). Additionally, the lower charge cut-off voltage and higher discharge cut-off voltage facilitate the cycle performance. Collectively, the superior performance of LMROs//LMROs demonstrates a feasible and potential bi-functional electrode material for new symmetric lithium-ion battery.