New insights into the modification mechanism of Li-rich Li1.2Mn0.6Ni0.2O2 coated by Li2ZrO3

Abstract

Lithium-rich Mn-based layered cathode materials have attracted wide attention due to their high specific capacity for lithium-ion batteries. However, some critical issues i.e. poor rate capability and voltage fade have limited their practical applications. Herein, we propose a synchronous lithiation strategy to coat Li-rich Li_1.2Mn_0.6Ni_0.2O₂ (LMNO) with a thin layer of Li⁺-conductive Li₂ZrO₃. The obtained syn-Li₂ZrO₃@LMNO integrates the advantages of the Li₂ZrO₃ coating and Zr⁴⁺ doping, and shows a much higher rate capability and cycling stability than those of the counterpart post-Li₂ZrO₃@LMNO fabricated by a post-coating method. More importantly, the average voltage of syn-Li₂ZrO₃@LMNO has been enhanced by 0.15 V and the voltage decay has also been mitigated. New insights into the synergetic modification mechanism of the Li₂ZrO₃ coating and Zr⁴⁺ doping have been proposed. The coating layer of Li⁺-conductive Li₂ZrO₃ alleviates the surface side reactions, suppresses the transition metal dissolution and enhances the Li-ion conductivity. Meanwhile, the doping and incorporation of Zr⁴⁺ into the host structure accompanied by the Li₂ZrO₃ coating expands the interplanar spacing and decreases Li/Ni mixing which facilitates Li⁺ diffusion. In addition, the integration of the Li₂ZrO₃ coating and Zr⁴⁺ doping also further enhances the layered structure stability and mitigates the voltage fade during lithiation/delithiation cycles. Moreover, the proposed synchronous lithiation coating route avoids the duplicated high-temperature calcinations and can also be widely used to modify some other cathode materials.