Complementary Effects of Mg and Cu Incorporation in Stabilizing the Cobalt-Free LiNiO2 Cathode for Lithium-Ion Batteries

Since the discovery of LiNiO₂ several decades ago, a new era of electric vehicles demanding high-energy-density lithium-ion batteries (LIBs) has recently rebooted the interest in this cathode material to eliminate the dependence on expensive and scarcely available cobalt. However, LiNiO₂ has been plagued by cycle instability, thermal instability, and air instability. We present here an exploration of the mutual interaction of magnesium and copper in stabilizing the cobalt-free LiNiO₂ cathode. Although Mg doping is beneficial for the robustness of the bulk structure of LiNiO₂, surface characterization results of Mg-doped LiNiO₂ implies the need for further surface protection. To that end, we have incorporated Cu in addition to Mg in that Cu stabilizes the surface of Mg-doped LiNiO₂ by forming a protective stable surface layer without harming the bulk. Notable variations of the surface residual lithium composition (Li_Li2CO3/Li_LiOH) along with the incorporation of stabilizers are also discussed. The harmony between Mg and Cu with as little as 0.5 atom % Mg and 0.3 atom % Cu significantly enhances the specific energy and cycle life of LiNiO₂. This study demonstrates how the co-incorporation of optimal dopants can help stabilize both the bulk and surface and provides new insights toward developing cobalt-free layered oxide cathodes for high-energy-density LIBs.