Lithium-rich cathode materials have attracted great interests due to their advantages, such as high energy density and wide voltage window. However, their shortcomings like low initial coulombic efficiency and poor cycle performance have hindered their commercial application. Lithium-rich cathode materials Li_1.2Ni_0.13Co_0.13Mn_0.54O_2-xCl_x (x=0, 0.025, 0.050, 0.100) with different molar ratios of chloride ion (Cl^-) doping were prepared by a co-precipitation method. The regulation mechanism of Cl^- doping on the improvement of the electrochemical performance was investigated by X-ray photoelectron spectroscopy, in-situ X-ray diffraction and galvanostatic intermittent titration analysis. Compared with the pristine material, the initial coulombic efficiency of the cathode material with Cl-doping in a molar ratio of 0.05 increases from 72.8% to 81.5% at 0.2 C, and the capacity retention increases from 57.9% to 79.1% after 200 cycles at 1 C. It is indicated that Cl-doping can regulate the electrochemical behavior of O^2- by oxidizing the more into O^n- (n<2) and less production of oxygen gas, thus reducing the structural deterioration. Meanwhile, the larger ion radius of Cl^- can expand the layer spacing, reduce the polarization and accelerate the lithium ions diffusion in the lithium-rich and manganese-based cathode material, thereby enhancing the initial coulombic efficiency and the cycle performance.

P2-type layered Na_0.67MnO₂ has been considered to be a promising candidate cathode material for sodium ion batteries. Nevertheless, the undesired phase transitions during operation and the large Na⁺ radius induced sluggish ion diffusion remain the stumbling blocks to realize its high performance. Herein, we propose a Zn/Mg co-doping strategy, which is proved to have bifunctional effects. First, relative to the pristine P2-Na_0.67MnO₂ and the single-ion (Zn/Mg) doped samples, the Zn/Mg dual-doped P2-Na_0.67MnO₂ demonstrates a lower Mn³⁺/Mn⁴⁺ ratio and a higher lattice O content, which facilitate the structural stability of the cathode material. More intriguingly, the Zn/Mg co-doping gives rise to enlarged interplanar spacing, which provides spacious ion diffusion channels for fast Na⁺ intercalation/extraction. As a result, the Zn/Mg dual-doped sample exhibits a high Na⁺ diffusion coefficient and a solid-solution reaction during charge/discharge, with a cell volume change determined to be only 0.55%. Taking advantages of the above favorable features, the Zn/Mg dual-doped P2-Na_0.67MnO₂ demonstrates a high rate performance with 67.2 mAhdg^-1 delivered at 10 C and a decent cycling stability with a capacity retention of 93.8% achieved at 1 C after 100 cycles. This work introduces the Zn/Mg co-doping strategy to simultaneously improve the cycling stability and rate capability of P2-Na_0.67MnO₂, which may offer a promising avenue for further performance enhancement of the layered Na-ion batteries cathode materials.

Improving catalytic activity and durabilty through the structural and compositional development of bifunctional electrocatalysts with low cost, high activity and stability is a challenging issue in electrochemical water splitting. Herein, we report the fabrication of heterostructured P-CoMoO₄@NiCoP on a Ni foam substrate through interface engineering, by adjusting its composition and architecture. Benefitting from the tailored electronic structure and exposed active sites, the heterostructured P-CoMoO₄@NiCoP/NF arrays can be coordinated to boost the overall water splitting. In addition, the superhydrophilic and superaerophobic properties of P-CoMoO₄@NiCoP/NF make it conducive to water dissociation and bubble separation in the electrocatalytic process. The heterostructured P-CoMoO₄@NiCoP/NF exhibits excellent bifunctional electrocatalysis activity with a low overpotential of 66 ​mV at 10 ​mA ​cm⁻² for HER and 252 ​mV at 100 ​mA ​cm⁻² for OER. Only 1.62 ​V potential is required to deliver 20 ​mA ​cm⁻² in a two-electrode electrolysis system, providing a decent overall water splitting performance. The rational construction of the heterostructure makes it possible to regulate the electronic structures and active sites of the electrocatalysts to promote their catalytic activity.