High-voltage high-nickel lithium layered oxide cathodes show great application prospects to meet the ever-increasing demand for further improvement of the energy density of rechargeable lithium-ion batteries (LIBs) mainly due to their high output capacity. However, severe bulk structural degradation and undesired electrode-electrolyte interface reactions seriously endanger the cycle life and safety of the battery. Here, 2 mol% Ti atom is used as modified material doping into LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) to reform LiNi_0.6Co_0.2Mn_0.18Ti_0.02O₂ (NCM-Ti) and address the long-standing inherent problem. At a high cut-off voltage of 4.5 V, NCM-Ti delivers a higher capacity retention ratio (91.8% vs. 82.9%) after 150 cycles and a superior rate capacity (118 vs. 105 mAh·g-1) at the high current density of 10 C than the pristine NCM. The designed high-voltage full battery with graphite as anode and NCM-Ti as cathode also exhibits high energy density (240 Wh·kg-1) and excellent electrochemical performance. The superior electrochemical behavior can be attributed to the improved stability of the bulk structure and the electrode-electrolyte interface owing to the strong Ti-O bond and no unpaired electrons. The in-situ X-ray diffraction analysis demonstrates that Ti-doping inhibits the undesired H2-H3 phase transition, minimizing the mechanical degradation. The ex-situ TEM and X-ray photoelectron spectroscopy reveal that Ti-doping suppresses the release of interfacial oxygen, reducing undesired interfacial reactions. This work provides a valuable strategic guideline for the application of high-voltage high-nickel cathodes in LIBs.

Developing an efficient non-noble bifunctional electrocatalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in the same electrolyte is significant for lowering the cost of electrochemical water splitting. Herein, a phase-pure pentlandite Ni_4.3Co_4.7S₈ bifunctional electrocatalyst was synthesized via a hydrothermal process using a commercial nickel foam as the nickel source. The active metallic nickel source and the chelating agent ethylenediamine play important roles in the formation of phase-pure pentlandite Ni_4.3Co_4.7S₈ binary sulfide. Physicochemical characterizations, electrochemical measurements and density functional theory (DFT) computations illustrate that the material has an exposed high-indexed (022) surface with a biomimetic hydrogenase-like structure, and that the pentlandite phase has metallic characteristics, with next-nearest neighbor metal–metal bonds, as well as there being a high overlap of density of state (DOS) at the Fermi-level due to the synergistic effect between Ni and Co ions. In addition, there is an elevation of the d-state center (from −2.84 to −1.52 eV) with high occupation of the anti-bonding e_g (d_x²−y² and d_z²) d-orbitals. These properties endow the Ni_4.3Co_4.7S₈ bifunctional electrocatalyst with higher catalytic activity for OER than RuO₂, with comparative activity for HER to commercial Pt/C and with a low over-potential for all water splitting in an alkaline electrolyte. The studies here provide a novel strategy to synthesise phase-pure pentlandite nickel cobalt binary sulfides and boost their applications in electrochemical water splitting.

Metal-ionic-conductor K₂Fe₄O₇ (KFO) with instinct superhydrophilic properties was hydrothermally grown on nickel foam (NF), the formed binder-free nano-KFO/NF can deliver extremely large current density for water splitting.