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Na super ionic conductor (NASICON)-type Na3V2(PO4)3 (NVP) has been considered as a potential positive electrode material for sodium ion batteries (NIBs) owing to its high theoretical specific capacity. Nonetheless, the practical application of NVP is hindered by the intrinsically poor electronic conductivity. Herein, polydopamine-derived nitrogen-doped carbon-covered Na3V2(PO4)3/C composites (NVP/C/NC) have been prepared through a self-polymerization of dopamine on the NVP/C surface and subsequent calcination at high temperature. The as-synthesized NVP/C/NC composite cathode exhibits a high initial reversible capacity (109.2 mAh/g at 0.2C), superior rate performance (87.2 mAh/g at a rate up to 20C), and excellent cycling capability (91.2% of the initial capacity is kept after 500 cycles at 2C) in NIBs. Furthermore, compared with NVP/C electrode, the NVP/C/NC electrode presents low resistance and high sodium ions diffusion coefficient. The good performance can be ascribed to the nitrogen-doped carbon layer in improving the electronic conductivity, shortening diffusion length of Na+ ions and electrons, and relieving the volume changes of electrode materials. These preliminary results suggest that the as-obtained NVP/C/NC composite is a novel promising electrode material for low-cost sodium energy storage.

Free-standing Co3O4 on nickel foam is synthesized by a simple hydrothermal route, using cobalt nitrate hexahydrate as the cobalt source, and urea as the precipitator. The effects of urea on the structural and electrochemical characteristics are investigated in detail. As the urea increased, the morphology of the free-standing Co3O4 turns from hexagonal nanosheets to nanoflakes, and finally turns to nanoflakes/nanowires hybrid structure. This hybrid structure is made up of ultrathin porous nanoflakes, and short nanowires anchored at the edge of the nanoflakes, which may enhance the diffusion rate of the electrolyte and O2 and provide more active sites for both O2 reduction and evolution reactions. When applied as a free-standing cathode for the Li O2 cells, it shows better performance for the nanoflakes/nanowires hybrid structure than the others. It exhibits a high specific capacity of 5958 mA h g−1 at 0.1 mA cm−2, a long cycle life of 108 cycles with a limited capacity of 500 mA h g−1, and unique morphology of the discharge products.

Hollow MoO2 /reduced graphene oxide (MoO2 /rGO) sub-microsphere composites have been fabricated through a simple hydrothermal approach followed by a heat treatment process. When employed as an anode material for potassium-ion batteries, the as-synthesized MoO2 /rGO composite can deliver an initial charge specific capacity of 367.2 mAh g-1 at 50 mA g-1 , and its reversible capacity is 218.9 mAh g-1 after 200 cycles. Even when cycled at 500 mA g-1 , a high charge specific capacity of 104.2 mAh g-1 is achieved after 500 cycles. The excellent cycling capability and rate performance may be ascribed to the synergistic effects of the reduced graphene oxide and the hollow MoO2 spheres, which can increase the electrical conductivity of the composite, as well as resisting the strain arising from the repeated discharge-charge processes. These results indicate that the MoO2 /rGO hollow sphere composites are promising negative electrode materials for potassium-ion batteries.

Manganese-based layered KxMnO2 (x = 0.3 and 0.45) cathodes with P2/P3-type structure for K-ion batteries are prepared through a simple co-precipitation method. It is discovered that the amount of K not only plays an important role in the structure and morphology of the samples, but also has a certain effect on the electrochemical performance. In spite of the same synthesis conditions, the K0.45MnO2 sample displays different structure and smaller particle sizes in comparison with that of the K0.3MnO2 sample. The redox potentials of the two samples are almost the same. Both of them present excellent cycle stability and rate performance when tested as cathodes for K-ion batteries. However, K0.45MnO2 shows slightly better performance than that of K0.3MnO2. It can deliver a reversible specific capacity of 128.6 mAh g−1 at 20 mA g−1 with an average voltage of 2.75 V vs. K/K+. In addition, the K0.45MnO2 exhibits a fast rate performance with a specific capacity of 51.2 mAh g−1 even at 200 mA g−1, which exceeds the performance of some reported metal-based oxide cathodes. These results may provide new insight into developing manganese-based oxides cathode materials for K-ion batteries.

To enable lithium–oxygen batteries for practical applications, the design and efficient synthesis of nonprecious metal catalysts with high activity and stable structural properties are demanded. The objective is to accelerate the sluggish kinetics of both oxygen reduction reaction and oxygen evolution reaction by facilitating electronic/ionic transport and improving oxygen diffusion in a porous structure. In this study, high-surface-area and porous cobalt phosphide (Co2P) nanosheets are synthesized via an environmentally safe hydrothermal method, where red phosphorous is used as the phosphorous source. It was found that the as-prepared Co2P/acetylene black (AB) composite delivered enhanced electrochemical performances, such as high capacities of 2551 mA h g–1 (based on the total weight of Co2P and AB) or 5102 mA h g–1 (based on the weight of Co2P or AB) and a good cycle life of more than 1800 h (132 cycles) in lithium–oxygen battery. The rational design of the Co2P/AB porous oxygen electrode structure pro...

A layered potassium vanadate K0.23V2O5 has been successfully prepared by the hydrothermal method and evaluated as an anode material for lithium-ion and potassium-ion batteries. High structural stability is demonstrated by the ex situ X-ray diffraction (XRD) and ex situ scanning electron microscopy (SEM). When used as an anode material for lithium-ion batteries, the K0.23V2O5 exhibits a reversible capacity of 480.4 mAh g−1 at 20 mA g−1 after 100 cycles and 439.7 mAh g−1 at 200 mA g−1 after 300 cycles as well as good cycling stability. Even at a high current density of 800 mA g−1, a high reversible capacity of 202.5 mAh g−1 can be retained, indicating excellent rate performance. Whereas in potassium-ion batteries, it retains a capacity of 121.6 mAh g−1 after 150 cycles at 20 mA g−1 and 97.6 mAh g−1 at 100 mA g−1 after 100 cycles. Such superior electrochemical performance of K0.23V2O5 can be ascribed to the special flower-like morphology and structure. Overall, the results highlight the great potential of K0.23V2O5 as an anode material for both lithium-ion and potassium-ion batteries.

Highly mesoporous cobalt oxide nanosheets are grown on nickel foam (M-Co3O4/NF) by a hydrothermal method. Ag nanoparticles with 10–50 nm diameters are uniformly distributed on the surface of the mesoporous Co3O4 nanosheets (Ag/M-Co3O4/NF) after chemical bath reaction. Moreover, we discovered that the homogeneous distribution of Ag nanoparticles on free-standing, highly mesoporous Co3O4 nanosheets showed the synergistic effect of the high electrocatalyst reactions toward the ORR from Ag and OER from M-Co3O4. Highly mesoporous Co3O4 nanosheets with a thickness of 10 nm as free-standing cathode for Li-O2 battery are beneficial to accommodating insoluble discharge products and facilitating oxygen diffusion and electrolyte impregnation. Ag nanoparticles can improve the electrical conductivity of the O2 electrode and provide a catalytic activity for ORR at the same time. The Ag/M-Co3O4/NF exhibited a robust catalytic activity as cathode for Li-O2 batteries with a high reversible capacity of 2471.1 mA h g−1, a low discharge/charge overpotential, and a cycle life of 124 cycles (under the curtaining capacity of 500 mA h g−1). The preliminary results indicate that Ag/M-Co3O4/NF is an efficient and stable bifunctional cathode for Li-O2 batteries.

A novel layered ternary material K0.67Ni0.17Co0.17Mn0.66O2 has been fabricated via a co-precipitation assisted solid-phase method and further evaluated as a cathode for potassium-ion batteries for the first time. Highly reversible K+ intercalation/deintercalation is demonstrated in this material. It delivers a reversible capacity of 76.5mAh/g with average voltage of 3.1V and shows good cycling performance with capacity retention of 87% after 100cycles at 20mA/g. This work may give a new insight into developing cathode materials for potassium-ion batteries. Keywords: Potassium-ion batteries, Cathode, Ternary material, K0.67Ni0.17Co0.17Mn0.66O2

Traditionary oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) electrocatalysts are mainly precious metal materials, but their expensive cost and low amount of storing limit their applications in Li–O2 batteries. Here is a simple way to report that we synthesis cobalt nanoparticle in-situ encapsulated into N-doped carbon polyhedral (Co@NC) by pyrolyzing ZIF-67 and we find that 900 °C is the optimal temperature for pyrolysis. The Co@NC and Co@NC-900/acetylene black (AB) is used as a bifunctional electrocatalysts and an oxygen electrode in Li–O2 batteries respectively. The Co@NC-900/AB can be the promising non-noble-metal-based oxygen electrode in Li–O2 batteries.

A series of iron-substituted layered P3-type manganese oxides, K0.45Mn1−xFexO2 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were fabricated using a convenient solid-state method and studied as cathode materials for potassium-ion batteries. The microstructure and morphology of the as-synthesized materials were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The electrochemical characteristics of K0.45Mn1−xFexO2 samples have been investigated systematically and K0.45Mn0.8Fe0.2O2 shows the best cyclic stability and highest rate performance. It delivers a large reversible discharge capacity of 106.2 mAh g−1 at 20 mA g−1 with a capacity retention rate of 77.3% after 100 cycles. It also presents obviously enhanced rate performance with the capacity of 64.9 mAh g−1 at 200 mA g−1 and stable cycling capability of 44.7 mAh g−1 after 100 cycles. The results demonstrate that the relatively small substitution (20%) at the transition metal site can improve the cycle stability during potassium ions insertion and extraction. Therefore, the layered P3-K0.45Mn0.8Fe0.2O2 possibly serves as a potentially promising cathode material that made from completely earth-abundant elements for potassium-ion batteries applications.