Sodium-ion batteries (SIBs) have attracted much interest as a low-cost and environmentally benign energy storage system, but more attention is justifiably required to address the major technical issues relating to the anode materials to deliver high reversible capacity, superior rate capability, and stable cyclability. A SnSe/reduced graphene oxide (RGO) nanocomposite has been prepared by a facile ball-milling method, and its structural, morphological, and electrochemical properties have been characterized and compared with those of the bare SnSe material. Although the redox behavior of SnSe remains nearly unchanged upon the incorporation of RGO, its electrochemical performance is significantly enhanced, as reflected by a high specific capacity of 590 mA h g⁻¹ at 0.050 A g⁻¹, a rate capability of 260 mA h g⁻¹ at 10 A g⁻¹, and long-term stability over 120 cycles. This improvement may be attributed to the high electronic conductivity of RGO, which also serves as a matrix to buffer changes in volume and maintain the mechanical integrity of the electrode during (de)sodiation processes. In view of its excellent Na⁺ storage performance, this SnSe/RGO nanocomposite has potential as an anode material for SIBs.

Silver molybdate, Ag₂Mo₂O₇, has been prepared by a conventional solid-state reaction. Its electrochemical properties as an anode material for sodium-ion batteries (SIBs) have been comprehensively examined by means of galvanostatic charge–discharge cycling, cyclic voltammetry, and rate performance measurements. At operating voltages between 3.0 and 0.01 V, the electrode delivered a reversible capacity of nearly 190 mA h g⁻¹ at a current density of 20 mA g⁻¹ after 70 cycles. Ag₂Mo₂O₇ also demonstrated a good rate capability and long-term cycle stability, the capacity reaching almost 100 mA h g⁻¹ at a current density of 500 mA g⁻¹, with a capacity retention of 55 % over 1000 cycles. Moreover, the sodium storage process of Ag₂Mo₂O₇ has been investigated by means of ex situ XRD, Raman spectroscopy, and HRTEM. Interestingly, the anode decomposes into Ag metal and Na₂MoO₄ during the initial discharge process, and then Na⁺ ions are considered to be inserted into/extracted from the Na₂MoO₄ lattice in the subsequent cycles governed by an intercalation/deintercalation mechanism. Ex situ HRTEM images revealed that Ag metal not only remains unchanged during the sodiation/desodiation processes, but is well dispersed throughout the amorphous matrix, thereby greatly improving the electronic conductivity of the working electrode. The “in situ” decomposition behavior of Ag₂Mo₂O₇ is distinct from that of chemically synthesized, metal-nanoparticle-coated electrode materials, and provides strong supplementary insight into the mechanism of such new anode materials for SIBs and may set a precedent for the design of further materials.

Cu₃V₂O₈ nanoparticles with particle sizes of 40–50 nm have been prepared by the co-precipitation method. The Cu₃V₂O₈ electrode delivers a discharge capacity of 462 mA h g⁻¹ for the first 10 cycles and then the specific capacity, surprisingly, increases to 773 mA h g⁻¹ after 50 cycles, possibly as a result of extra lithium interfacial storage through the reversible formation/decomposition of a solid electrolyte interface (SEI) film. In addition, the electrode shows good rate capability with discharge capacities of 218 mA h g⁻¹ under current densities of 1000 mA g⁻¹. Moreover, the lithium storage mechanism for Cu₃V₂O₈ nanoparticles is explained on the basis of ex situ X-ray diffraction data and high-resolution transmission electron microscopy analyses at different charge/discharge depths. It was evidenced that Cu₃V₂O₈ decomposes into copper metal and Li₃VO₄ on being initially discharged to 0.01 V, and the Li₃VO₄ is then likely to act as the host for lithium ions in subsequent cycles by means of the intercalation mechanism. Such an “in situ” compositing phenomenon during the electrochemical processes is novel and provides a very useful insight into the design of new anode materials for application in lithium-ion batteries.

Li-rich layered oxide Li_1.18Ni_0.15Co_0.15Mn_0.52O₂ (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium-ion battery and its Na⁺ storage properties are comprehensively studied in terms of galvanostatic charge–discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium-ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g⁻¹ at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g⁻¹ for 200 cycles at 5 C rate. Moreover, ex situ ICP-OES suggests interesting mixed-ions migration processes: In the initial two cycles, only Li⁺ can intercalate into the LNCM cathode, whereas both Li⁺ and Na⁺ work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge–discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium-ion batteries.

Tin–iron–carbon nanocomposite is successfully prepared by a sol–gel method followed by a chemical vapor deposition (CVD) process with acetylene gas as the carbon source. The structural properties, morphology, and electrochemical performances of the nanocomposite are comprehensively studied in comparison with those properties of tin–carbon and iron–carbon nanocomposites. Sheet-like carbon architecture and different carbon contents are induced thanks to the catalytic effect of iron during CVD. Among three nanocomposites, tin–iron–carbon demonstrates the highest reversible capacity of 800 mA h g⁻¹ with 96.9 % capacity retention after 50 cycles. It also exhibits the best rate capability with a discharge capacity of 420 mA h g⁻¹ at a current density of 1000 mA g⁻¹. This enhanced performance is strongly related to the carbon morphology and content, which can not only accommodate the large volume change, but also improve the electronic conductivity of the nanocomposite. Hence, the tin–iron–carbon nanocomposite is expected to be a promising anode for lithium-ion batteries.