Carbon coated K0.8Ti1.73Li0.27O4 (KTLO) has been synthesized by a facile flux method followed by ball-milling and gaseous carbon coating. The carbon coated KTLO delivers a reversible specific capacity of 119.6 mA h g−1 at 20 mA g−1 with no capacity loss after 250 cycles as an anode material in sodium ion batteries, exhibiting an improved rate capability of 66 mA h g−1 at 200 mA g−1. It was found that carbon coating of KTLO not only enhances its electronic conductivity, but also improves the structure stability, proving that the carbon coated KTLO is a promising anode material for sodium ion batteries.

•NaxFeFe(CN)6 nanocubes with various Na content are synthesized via a facile coprecipitation method.•Na+ ions may intercalate into multiple sites on 8c and 24d sites in Na-rich NaxFeFe(CN)6.•The coordination environment has a great effect on extraction of Na+ ions.•Na-rich NaxFeFe(CN)6 as cathodes exhibit excellent electrochemical performance.Na-rich prussian blue analogues (PBs) with high coulombic efficiency are of fundamental and technological importance for sodium-ion batteries (SIBs). Here we report high-quality NaxFeFe(CN)6 nanocubes as cathode materials for SIBs and investigate their sodium storage mechanism. Among them, Na-rich Na1.70FeFe(CN)6 shows highly reversible electrochemical reactions, delivering a capacity as high as 120.7 mA h g−1 at a current density of 200 mA g−1; even at 1200 mA g−1, the capacity still retains up to 73.6 mA h g−1. The first-cycle coulombic efficiency strongly depends on the sodium content in NaxFeFe(CN)6. Experimental results and first-principle calculations demonstrate that sodium cations in the large cavities of PBs have a priority to occupy the 8c site, while in the Na-rich samples, Na+ ions can be pushed into other 24d site. We believe that our findings can provide new insights into sodium storage mechanism for the PBs.High-quality sodium iron hexacyanoferrate nanocubes with different sodium content have been successfully synthesized via a facile coprecipitation method. It is demonstrated that Na+ ions may occupy multiple sites in the cubic structure of Na-rich NaxFeFe(CN)6, and the coulombic efficiency strongly depends on the sodium content.

A porous hard carbon material was synthesized by the simple pyrolysis of H3PO4-treated biomass, i.e., pomelo peels, at 700 °C in N2. The as-obtained hard carbon had a 3D connected porous structure and a large specific surface area of 1272 m2 g−1. XPS analysis showed that the carbon material was functionalized by O-containing and P-containing groups. The porous hard carbon was used as an anode for sodium ion batteries and exhibited good cycling stability and rate capability, delivering a capacity of 181 mA h g−1 at 200 mA g−1 after 220 cycles and retaining a capacity of 71 mA h g−1 at 5 A g−1. The sodium storage mechanisms of the porous hard carbon can be explained by Na+ intercalation into the disordered graphene layers, redox reaction of the surface O-containing functional groups and Na+ storage in the nanoscale pores. However, the porous hard carbon demonstrated a low coulombic efficiency of 27%, resulting from the formation of a solid electrolyte interphase film and the side reactions of surface phosphorus groups.

A facile process is developed to synthesize MoS2 in basic solutions via a hydrothermal route by employing ammonium heptamolybdate and thiourea as starting materials and post-annealing in a N2 atmosphere at 450 °C for 5 h. The morphologies of the MoS2 products can be tuned from porous flowers to dense spheres by addition of NaOH. Experimental results show that the MoS2 products have good crystallinity. A formation mechanism of the MoS2 is proposed in which the dense MoS2 spheres are evolved from the porous MoS2 flowers through growth along the 〈00l〉 direction of the nanosheets. Based on the growth mechanism, the microstructure of MoS2 can be successfully controlled by adjustment of the S/Mo ratio or addition of a surfactant in the recipe. Electrochemical measurements demonstrate that the flower-like MoS2 shows better electrochemical performance than MoS2 spheres as anode materials for Li-ion batteries, which deliver a high reversible capacity of 900 mA h g−1 at a current density of 100 mA g−1, excellent cycling stability and rate capability.

•Dual phase Li4Ti5O12/TiO2 nano-composite is synthesized by a gacilehydrothermal approach.•The dual phase formation mechanism is proposed by the inhomogeneous Li distribution.•The phase composition can be tuned by the solution composition.A facile hydrothermal approach has been developed to synthesize the nanostructured dual phase Li4Ti5O12/TiO2 composite. The fabrication process simply involves the hydrothermal treatment of tetrabutyl titanate with LiOH in glycerol-water solution and a subsequent calcination procedure. The calcination treatment at 500 °C leads to the phase evolution from Li1.81H0.19Ti2O5•nH2O to Li4Ti5O12/TiO2 composite with a particle size of about 30 nm. It is found that glycerol as chelating agent plays an important role in the formation of TiO2. The Li4Ti5O12 and anatase TiO2 nano-composite exhibits rich hierarchical pores and a specific surface area of 91.88 m2 g−1, delivers ultrahigh rate performance of over 150 mA h g−1 at 20 C, as well as superior capacity retention of 151.4 mAh g−1 after 100 cycles at 1 C. It is therefore concluded that Li4Ti5O12/TiO2 nano-composite is a promising candidate for applications in high rate lithium ion batteries.

•Hierarchical layered K0.27MnO2 has been synthesized via a facile topochemical reaction.•Aqueous NaTi2(PO4)3/K0.27MnO2 sodium-ion full cell exhibits excellent performance.•Na-insertion mechanism in K0.27MnO2 is proposed.•K0.27MnO2 shows potential application in large-scale low-cost energy storage devices.Hierarchical layered K0.27MnO2 microflowers are firstly synthesized via a facile and efficient route based on a topochemical reaction process. As cathode materials for aqueous sodium-ion battery, such microflowers exhibit high reversible capacity, long cyclic life and excellent rate capability. After 100 cycles, a reversible capacity of 68.5 mA h g–1 at a current density of 0.2 A g–1 is attained in a full cell with K0.27MnO2 as cathode and NaTi2(PO4)3 as anode. We propose a sodium storage mechanism in K0.27MnO2 by analyzing the evolution of structure and interface during charge/discharge process.

Coral-like α-MnS composites with nitrogen-doped carbon (NC) were designed as anode materials for lithium-ion batteries. A facile two-step method was developed to synthesize the composites. Hydrothermally obtained polyvinyl pyrrolidone (PVP) capped (NH4)2Mn2(SO4)3 was used as a precursor. The α-MnS–NC composites were attained by heating the precursor at different temperatures for an appropriate time in a N2 atmosphere. The microstructure and morphology were carefully investigated by means of field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). As anode materials, the α-MnS–NC composites exhibit large reversible capacity, excellent cyclic stability and high rate capability. At a current density of 500 mA g−1, the discharge capacity reaches as high as 878 mA h g−1 at the first cycle and remains at 699 mA h g−1 even after 400 cycles.

A porous hard carbon material was synthesized by the simple pyrolysis of H3PO4-treated biomass, i.e., pomelo peels, at 700 °C in N2. The as-obtained hard carbon had a 3D connected porous structure and a large specific surface area of 1272 m2 g−1. XPS analysis showed that the carbon material was functionalized by O-containing and P-containing groups. The porous hard carbon was used as an anode for sodium ion batteries and exhibited good cycling stability and rate capability, delivering a capacity of 181 mA h g−1 at 200 mA g−1 after 220 cycles and retaining a capacity of 71 mA h g−1 at 5 A g−1. The sodium storage mechanisms of the porous hard carbon can be explained by Na+ intercalation into the disordered graphene layers, redox reaction of the surface O-containing functional groups and Na+ storage in the nanoscale pores. However, the porous hard carbon demonstrated a low coulombic efficiency of 27%, resulting from the formation of a solid electrolyte interphase film and the side reactions of surface phosphorus groups.

Carbon coated K0.8Ti1.73Li0.27O4 (KTLO) has been synthesized by a facile flux method followed by ball-milling and gaseous carbon coating. The carbon coated KTLO delivers a reversible specific capacity of 119.6 mA h g−1 at 20 mA g−1 with no capacity loss after 250 cycles as an anode material in sodium ion batteries, exhibiting an improved rate capability of 66 mA h g−1 at 200 mA g−1. It was found that carbon coating of KTLO not only enhances its electronic conductivity, but also improves the structure stability, proving that the carbon coated KTLO is a promising anode material for sodium ion batteries.

A facile process is developed to synthesize MoS2 in basic solutions via a hydrothermal route by employing ammonium heptamolybdate and thiourea as starting materials and post-annealing in a N2 atmosphere at 450 °C for 5 h. The morphologies of the MoS2 products can be tuned from porous flowers to dense spheres by addition of NaOH. Experimental results show that the MoS2 products have good crystallinity. A formation mechanism of the MoS2 is proposed in which the dense MoS2 spheres are evolved from the porous MoS2 flowers through growth along the 〈00l〉 direction of the nanosheets. Based on the growth mechanism, the microstructure of MoS2 can be successfully controlled by adjustment of the S/Mo ratio or addition of a surfactant in the recipe. Electrochemical measurements demonstrate that the flower-like MoS2 shows better electrochemical performance than MoS2 spheres as anode materials for Li-ion batteries, which deliver a high reversible capacity of 900 mA h g−1 at a current density of 100 mA g−1, excellent cycling stability and rate capability.

Coral-like α-MnS composites with nitrogen-doped carbon (NC) were designed as anode materials for lithium-ion batteries. A facile two-step method was developed to synthesize the composites. Hydrothermally obtained polyvinyl pyrrolidone (PVP) capped (NH4)2Mn2(SO4)3 was used as a precursor. The α-MnS–NC composites were attained by heating the precursor at different temperatures for an appropriate time in a N2 atmosphere. The microstructure and morphology were carefully investigated by means of field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). As anode materials, the α-MnS–NC composites exhibit large reversible capacity, excellent cyclic stability and high rate capability. At a current density of 500 mA g−1, the discharge capacity reaches as high as 878 mA h g−1 at the first cycle and remains at 699 mA h g−1 even after 400 cycles.