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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 (LiLi2CO3/LiLiOH) along with the incorporation of stabilizers are also discussed. The harmony between Mg and Cu with as little as 0.5 at % Mg and 0.3 at % 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 towards developing cobalt-free layered oxide cathodes for high-energy-density LIBs.