Layer-structured MoS₂ is regarded as a promising anode material for potassium ion batteries. Herein, MoS₂ nanosheets on N, P-codoping reduced graphene oxide (MoS₂/N, P-rGO) have been successfully prepared via a facile two-step synthesis, where few-layered MoS₂ nanosheets are chemically bonded onto the surface of N, P-rGO. As an anode material, MoS₂/N, P-rGO exhibits a high specific capacity (462.7 mAhdg^-1 at 100 mAdg^-1 over 200 cycles), outstanding rate capability (224.9 mAhdg^-1 at 20 Adg^-1), and excellent cycle life (236.6 mAhdg^-1 at 2 Adg^-1 after 7, 000 cycles), much better than those of MoS₂ and MoS₂/rGO. These advanced performances outperform most of the reported anode materials for potassium ion batteries to date. Meanwhile, the K-storage reactions of MoS₂/N, P-rGO have been disclosed through in-situ and ex-situ characterizations. The kinetics analysis confirms that K-storage of MoS₂/N, P-rGO is predominant by pseudo-capacitance.

Ti-based anode materials in sodium ion batteries have attracted extensive interests due to its abundant resources, low toxicity, easy synthesis and long cycle life. However, low coulombic efficiency and limited specific capacity affect their applications. Here, cubic-phase TiP₂O₇ is examined as anode materials, using in-situ/ex-situ characterization techniques. It is concluded that the redox reactions of Ti⁴⁺/Ti³⁺ and Ti³⁺/Ti⁰ consecutively occur during the discharge/charge processes, both of which are highly reversible. These reactions make the specific capacity of TiP₂O₇ even higher than the case of TiO₂ that only contains a simple anion, O^2-. Interestingly, Ti species participate only one of the redox reactions, due to the remarkable difference in local structures related to the sodiation process. The stable discharge/charge products in TiP₂O₇ reduce the side reactions and improve the coulombic efficiency as compared to TiO₂. These features make it a promising Ti-based anode for sodium ion batteries. Therefore, TiP₂O₇@C microflowers exhibit excellent electrochemical performances, ~ 109 mAh·g^-1 after 10,000 cycles at 2 A·g^-1, or 95.2 mAh·g^-1 at 10 A·g^-1. The results demonstrate new opportunities for advanced Ti-based anodes in sodium ion batteries.

Carbon-coated mesoporous Co₉S₈ nanoparticles supported on reduced graphene oxide (rGO) are successfully synthesized by a simple process. This composite makes full use of the protection of the carbon layer on the surface, the good conductivity and three-dimensional (3D) structure of rGO, the mesoporous structure and nanoscale size of Co₉S₈, thereby presenting the excellent electrochemical performances in potassium-ion batteries, 407.9 mAh·g^-1 after 100 cycles at 0.2 A·g^-1 and 215.1 mAh·g^-1 at 5 A·g^-1 in rate performances. After 1,200 cycles at 1.0 A·g^-1, this composite still remains a capacity of 210.8 mAh·g^-1. The redox reactions for potassium storage are revealed by ex-situ transmission electron microscope (TEM)/high-resolution TEM (HRTEM) images, selected area electron diffraction (SAED) patterns and X-ray photoelectron spectroscopy (XPS) spectra. The application of this composite as the host of sulfur for Li-S batteries is also explored. It sustains a capacity of 431.8 mAh·g^-1 after 800 cycles at 3 C, leading to a degradation of 0.052% per cycle. These results confirm the wide applications of this composite for electrochemical energy storage.

High-capacity anode materials are highly desirable for sodium ion batteries. Here, a porous Sb/Sb₂O₃ nanocomposite is successfully synthesized by the mild oxidization of Sb nanocrystals in air. In the composite, Sb contributes good conductivity and Sb₂O₃ improves cycling stability, particularly within the voltage window of 0.02–1.5 V. It remains at a reversible capacity of 540 mAh·g^–1 after 180 cycles at 0.66 A·g^–1. Even at 10 A·g^–1, the reversible capacity is still preserved at 412 mAh·g^–1, equivalent to 71.6% of that at 0.066 A·g^–1. These results are much better than Sb nanocrystals with a similar size and structure. Expanding the voltage window to 0.02–2.5 V includes the conversion reaction between Sb₂O₃ and Sb into the discharge/charge profiles. This would induce a large volume change and high structure strain/stress, deteriorating the cycling stability. The identification of a proper voltage window for Sb/Sb₂O₃ paves the way for its development in sodium ion batteries.

Galvanic replacement, one of the popular strategies for producing hollow metallic nanostructures, has enjoyed great success in the past. However, it is rarely used with Au nanoparticles as the self-sacrificed templates, even though these nanoparticles can be produced with well-controlled size, shape, and structure. Here, both Ag and Au from the core–shell Au@Ag nanorods are demonstrated to be involved in the galvanic replacement for producing hollow nanostructures. The enhanced oxidation of metallic Au could be attributed to the close contact between Au and Ag and the unique charge compensation from Au to Ag, both of which are indispensable for the etching of Au via galvanic replacement. As a result of this reaction, these bimetallic nanorods experience a structural evolution from nanorattles, to tip-empty nanorods, and eventually to porous nanotubes. The nanotubes exhibit high catalytic activities in the electrooxidation of formic acid. These results not only disclose the underlying mechanism by which metallic Au could be replaced under mild conditions, but also expand the selection of self-sacrificed templates for galvanic replacement, which is an important reaction in many applications.

Binary transition metal oxides are considered as promising anode materials for lithium-ion batteries (LIB), because they can effectively overcome the drawbacks of simple oxides. Here, a one-step hydrothermal method is described for the synthesis of regular ZnFe₂O₄ octahedrons about 200 nm in size at a low temperature without further annealing being required. The ZnFe₂O₄ octahedrons were characterized by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance of the ZnFe₂O₄ octahedrons was examined in terms of cyclic voltammetry and discharge/charge profiles. The ZnFe₂O₄ octahedrons exhibit a high capacity of 910 mA·h/g at 60 mA/g between 0.01 and 3.0 V after 80 cycles. They also deliver a reversible specific capacity of 730 mA·h/g even after 300 cycles at 1000 mA/g, a much better performance than those in previous reports. A set of reactions involved in the discharge/charge processes are proposed on the basis of ex situ high-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns of the electrode materials. The insights obtained will be of benefit in the design of future anode materials for lithium ion batteries.