Common preparation methods of manganese-based Li-rich layered oxides include co-precipitation, combustion, spray pyrolysis, and molten salt synthesis. Herein, we present a facile new reactive-templating route to prepare manganese-based lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 using β−MnO2 nanorod, which plays a dual role as reactive template as well as Mn-source. Rietveld refinement and electron diffraction patterns confirm the formation of phase pure, highly crystalline Li1.2Mn0.54Ni0.13Co0.13O2 with two integrated layered components of 0.5(Li2MnO3).0.5(LiMn1/3Ni1/3Co1/3O2). Electron microscopy studies reveal the formation of anisotropic rod-like crystals of 0.8–1.0 μm in length and ∼200 nm in thickness. The Li1.2Mn0.54Ni0.13Co0.13O2 nanorod as cathode for Li-ion battery, delivers an impressive reversible capacity of 223 mAh.g−1 at 0.1C rate after 150 cycles and 161 mAh.g−1 at 1 C rate after 300 cycles. Rapid structural transition from layered to spinel-like phase at high temperature (55 °C) leads to gradual decay in discharge capacity upon cycling, whereas low Li-ion diffusivity, cell resistance, and high viscosity hampers the performance at low temperature (5 °C). Impedance spectroscopy along with (dis)charge differential plots corroborate that activation of Li2MnO3 and Li-ion de(intercalation) into the MnO2 phase is very facile at high temperature (55 °C), which leads to high specific capacity, high coulombic efficiency, and high-power capability.