NCA (LiNi 0.85 Co 0.10 Al 0.05−x M x O 2 , M=Mn or Ti, < 0.01) cathode materials are prepared by a hydrothermal reaction at 170 ∘ C and doped with Mn and Ti to improve their electrochemical properties. The crystalline phases and morphologies of various NCA cathode materials are characterized by XRD, FE-SEM, and particle size distribution analysis. The CV, EIS, and galvanostatic charge/discharge test are employed to determine the electrochemical properties of the cathode materials. Mn and Ti doping resulted in cell volume expansion. This larger volume also improved the electrochemical properties of the cathode materials because Mn 4+and Ti 4+ were introduced into the octahedral lattice space occupied by the Li-ions to expand the Li layer spacing and, thereby, improved the lithium diffusion kinetics. As a result, the NCA-Ti electrode exhibited superior performance with a high discharge capacity of 179.6 mAh g −1 after the first cycle, almost 23 mAh g −1 higher than that obtained with the undoped NCA electrode, and 166.7 mAh g −1 after 30 cycles. A good coulombic efficiency of 88.6% for the NCA-Ti electrode is observed based on calculations in the first charge and discharge capacities. In addition, the NCA-Ti cathode material exhibited the best cycling stability of 93% up to 30 cycles.

The rational design and synthesis of multicomponent core@shell structures with fine morphology is a promising approach to develop electrode materials for advanced supercapacitors. In this study, Zn-Ni LDH@NiMoS x nanosheets with a hierarchical heterostructure are grown in situ on nickel foam through the hydrothermal routes, for the potential use as an integrated positive electrode material. The Zn-Ni LDH@NiMoS x shows a unique morphology and mesoporous feature with excellent synergistic effects between individual components. Compared to the single components of Zn-Ni LDH and NiMoS x , the Zn-Ni LDH@NiMoS x nanosheet arrays show better specific capacity (357.88 mA h g–1 at a current of 5 mA cm–2) and rate performance. Meanwhile, ZIF-8 derived 3D nanoporous N-doped carbon (ZPNC) material is used as an negative electrode material with high surface area (918.3 m2 g–1), excellent capacity (52.42 mA h g–1 at 2 mA cm–2), and rate performance (∼55% at 50 mA cm–2). The asymmetric supercapacitor device based on Zn-Ni LDH@NiMoS x and ZPNC electrodes exhibits a specific capacity of 73.18 mA h g–1 at 3.5 mA cm–2 and an excellent cycle lifespan of 90% after 6000 cycles. The device also demonstrates excellent energy density (58.54 W h kg–1) and very high power density (7397.34 W kg–1).

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The anionic components have a significant role in regulating the electrochemical properties of mixed transition-metal (MTM)-based materials. However, the relationship between the anionic components and their inherent electrochemical properties in MTM-based materials is still unclear. Herein, we report the anion-dependent supercapacitive and oxygen evolution reaction (OER) properties of in situ grown binary Ni–Co–selenide (Se)/sulfide (S)/phosphide (P) nanosheet arrays (NAs) over nickel foam starting from MOF-derived Ni–Co layered double hydroxide precursors. Among them, the Ni–Co–Se NAs exhibited the best specific capacity (289.6 mA h g–1 at 4 mA cm–2). Furthermore, a hybrid device constructed with Ni–Co–Se NAs delivered an excellent energy density (74 W h kg–1 at 525 W kg–1) and an ultra-high power density (10 832 W kg–1 at 46 W h kg–1) with outstanding durability (∼94%) for 10 000 cycles. Meanwhile, the Ni–Co–Se NAs showed superior electrocatalytic OER outputs with the lowest overpotential (235 mV at 10 mA cm–2) and Tafel slope. In addition, Ni–Co–Se NAs outperformed IrO2 as an anode in an anion exchange membrane water electrolyzer at a high current density (>1.0 A cm–2) and exhibited a stable performance up to 48 h with a 99% Faraday efficiency. Theoretical analyses validate that the Se promotes OH adsorption and improves the electrochemical activity of the Ni–Co–Se through a strong electronic redistribution/hybridization with an active metal center due to its valence 4p and inner 3d orbital participations. This study will provide in-depth knowledge of bifunctional activities in MTM-based materials with different anionic substitutions.

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