Li-rich-layered oxide is considered to be one of the most promising cathode materials for high-energy lithium ion batteries. However, it suffers from poor rate capability, capacity loss, and voltage decay upon cycling that limits its utilization in practical applications. Surface properties of Li-rich-layered oxide play a critical role in the function of batteries. Herein, a novel and successful strategy for synchronous tailoring surface structure and chemical composition of Li-rich-layered oxide is proposed. Poor nickel content on the surface of carbonate precursor is initially prepared by a facile treatment of NH 3 ·H 2 O, which can retain at a certain low amount on the surface in the final lithiated Li-rich-layered oxide after a solid-phase reaction process. Moreover, a phase-gradient outer layer with "layered-coexisting phasespinel" structure toward to the outside surface is self-induced and formed synchronously based on poor nickel surface of the precursor. Electrochemical tests reveal this unique surface enables excellent cycling stability, improved rate capability, and slight voltage decay of cathodes. The finding here sheds light on a universal principle both for masterly tailoring surface structure and chemical composition at the same time for improving electrochemical performance of electrode materials.

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The serious shuttle effect, sluggish reduction kinetics of polysulfides and the difficult oxidation reaction of Li 2 S have hindered LiS battery practical application. Herein, a 3D hierarchical structure composed of NiMoO 4 nanosheets in situ anchored on NS doped carbon clothes (NiMoO 4 @NSCC) as the free-standing host is creatively designed and constructed for LiS battery. Dual transitional metal oxide (NiMoO 4 ) increases the electrons density near the Fermi level due to the contribution of the incorporating molybdenum (Mo), leading to the smaller bandgap, and thus stronger metallic properties compared with NiO. Furthermore, as a bidirectional catalyst, NiMoO 4 is proposed to facilitate reductions of polysulfides through lengthening the SS bond distance of Li 2 S 4 and reducing the free energy of polysulfides conversion, meanwhile promote critical oxidation of insulative discharge product (Li 2 S) via lengthening LiS bond distance of Li 2 S and decreasing Li 2 S decomposition barrier. Therefore, after loading sulfur (2 mg cm −2 ), NiMoO 4 @NSCC/S as the self-supporting cathode for the LiS battery exhibits impressive long cycle stability. This study proposes a concept of a bidirectional catalyst with dual metal oxides, which would supply a novel vision to construct the high-performance LiS battery.

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