A LiNiMnO cathode material with high surface orientation was prepared via a complexing reaction coupled with the elevated-temperature solid-state method. First, a bimetal-organic framework containing Ni and Mn ions was synthesized via a self-assembly route using pyromellitic acid (PMA) as a dispersant and complexing agent. This step was followed by calcination with lithium acetate using PMA as a structure-directing agent. The resulting LiNiMnO (M-LNMO) cathode material was investigated using X-ray diffraction, transmission and scanning electron microscopies, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. For comparison, LiNiMnO samples were prepared by coprecipitation and the solid-phase method under the same conditions. M-LNMO was highly crystalline with low impurity, uniform grain size, and a preferred orientation in the (111) and (110) planes. Owing to these advantages, the M-LNMO cathode material exhibited overwhelmingly high cyclic stability and rate capability and M-LNMO delivered a capacity of 145 mAh g at a discharge rate of 0.1C and a discharge capacity retention of 86.6% at 5C after 1000 cycles. Even at an extremely high discharge rate (10C), the specific capacity was 112.7 mAh g, and 78.7% of its initial capacity was retained over 500 cycles. The superior electrochemical performance, particularly during a low-rate operation, was conferred by improved crystallinity and the crystal orientation of the particles.

The slow Zn2+ intercalation/deintercalation kinetics in cathodes severely limits the electrochemical performance of aqueous zinc-ion batteries (ZIBs). Herein, we demonstrate a new kind of coordinately unsaturated manganese-based metal–organic framework (MOF) as an advanced cathode for ZIBs. Coordination unsaturation of Mn is performed with oxygen atoms of two adjacent −COO–. Its proper unsaturated coordination degree guarantees the high-efficiency Zn2+ transport and electron exchange, thereby ensuring high intrinsic activity and fast electrochemical reaction kinetics during repeated charging/discharging processes. Consequently, this MOF-based electrode possesses a high capacity of 138 mAh g–1 at 100 mA g–1 and a long life span (93.5% capacity retention after 1000 cycles at 3000 mA g–1) due to the above advantages. Such distinct Zn2+ ion storage performance surpasses those of most of the recently reported MOF cathodes. This concept of adjusting the coordination degree to tune the energy storage capability provides new avenues for exploring high-performance MOF cathodes in aqueous ZIBs.

In this work, a novel and facile one-pot method has been developed for the synthesis of a hybrid consisting of Ni-Mn-Co ternary oxide and poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT-PSS/NMCO) with a hierarchical three-dimensional net structure via a solvothermal-coprecipitation coupled with oxidative polymerization route. Apart from the achievement of polymerization, coprecipitation, and solvothermal in one pot, the hydroxyl (OH(-)) ions generated from the oxidative polymerization of organic monomer by neutral KMnO4 solution were skillfully employed as precipitants for metal ions. As compared with the PEDOT-PSS/Ni-Mn binary oxide, PEDOT-PSS/Co-Mn binary oxide, and PEDOT-PSS/MnO2, PEDOT-PSS1.5/NMCO exhibits overwhelmingly superior supercapacitive performance, more specifically, a high specific capacitance of 1234.5 F g(-1) at a current density of 1 A g(-1), a good capacitance retention of 83.7% at a high current density of 5 A g(-1) after 1000 cycles, an energy density of 51.9 W h kg(-1) at a power density of 275 W kg(-1), and an energy density of 21.4 W h kg(-1) at an extremely elevated power density of 5500 W kg(-1). Noticeably, the energy density and power density of PEDOT-PSS/NMCO are by far higher than those of the existing analogues recently reported. The exceptional performance of PEDOT-PSS/NMCO benefits from its unique mesoporous architecture, which could provide a larger reaction surface area, faster ion and electron transfer ability, and good structural stability. The desirable integrated performance enables the multicomponent composite to be a promising electrode material for energy storage applications.

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Because of the diversity of bonding properties between transition metal ions and multifunctional organic ligands, metal−organic frameworks (MOFs) with slow ion transport kinetics are considered as prospective materials for electrochemical energy storage. In this study, Ni−Mn-MOFs with a three-dimensional (3D) spherical structure were rationally synthesized via a hydrothermal method. The optimal electrode could provide rich redox active sites to guarantee enough Li + -storage capacity. The 3D microspheres assembled from MOF nanosheets not only provide an advantageous route for lithium-ion transport but the buffer volume also changes during the cycle because of the enhancement of electrochemical performance, resulting in a high capacity of 1380 mA h g −1 and an outstanding cycle life of 200 cycles. Additionally, the influence of the solvent content of the complex on the electrochemical properties of MOFs was also investigated. The results of this study provided insights and mechanistic explanations for the design of MOFs for lithium-ion battery applications.