Suppression of voltage decay and improvement in electrochemical performance by zirconium doping in li-rich cathode materials for li-ion batteries

Lithium manganese rich cathode materials (represented as xLi₂MnO₃-(1-x)LiMO₂, where M = Mn, Ni, Co) for Li-ion batteries have gained considerable research interests as they exhibit higher nominal voltage (∼4.0 V) and specific capacity (>250 mAhg⁻¹) as compared to commercially available cathodes. In the present work, we have studied the effect of zirconium ion doping in Li₂MnO₃ and Li_1.2Mn_0.55Ni_0.15Co_0.1O₂ (layered notation of 0.5Li₂MnO₃-0.5LiMn_0.375Ni_0.375Co_0.25O₂) cathode. As compared to its undoped counterpart Li_1.2Zr_0.008Mn_0.542Ni_0.15Co_0.1O₂ is found to yield superior cycleability, rate capability and voltage fade characteristics. Thus, capacity retention ∼78% is maintained in Zr doped LMR cathode after 100 charge-discharge cycles whereas for undoped LMR <30% capacity is retained after similar number of charge-discharge cycles. We have performed pre and post cycling X-ray diffraction, Raman spectroscopy, impedance spectroscopy, and dQ/dV analyses to understand the effect of Zr doping on the electrochemical performances of these LMR cathodes. We have demonstrated that the cycling induced layered to spinel phase transformation is substantially suppressed in Zr modified LMR cathodes and leads to their improved electrochemical performances. Also, as analyzed using galvanostatic intermittent titration technique, we have found that Zr doping increases the Li⁺ diffusion coefficient and thereby improves the rate performance of the doped LMR cathode.