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Rechargeable aqueous zinc-ion batteries (AZIBs) that directly use metallic zinc as anode and mildly acidic Zn2+-containing aqueous solutions as electrolytes have exhibited promising complementarity for well-established lithium-ion batteries. The fabrication of high-voltage, high-capacity, and durable cathode and stable anode are the burning issues of fabricating high-performance AZIBs. Herein, the small amount of dual-cation preintercalated and amorphous carbon confined vanadium dioxide (Ni0.006Ca0.0045VO2@C) was prepared for high-performance Zn2+-storage materials, and subsequent in situ electrochemical anodic oxidation strategy was used to convert Ni0.006Ca0.0045VO2@C to δ-(Ni,Ca)V2O5@C as high-capacity AZIB cathode. The elaborate architecture not only showed a high specific capacity of 433.8 mAh g−1 at 0.1 A g−1 but also retained a reversible capacity of 74 mAh g−1 after 4000 cycles at 5 A g−1. In addition, the Zn2+/H+ co-intercalation mechanism was also verified by employing ex situ XRD and ex situ XPS. Finally, the flexible quasi-solid-state ZIBs were also assembled with the Ni0.006Ca0.0045VO2@C as cathode and polyvinyl alcohol hydrogel as electrolyte, suggesting its promising application for the superior Zn2+-storage performance.

Metal phosphates, such as LiFePO4 (LFP), have been attracting extensive attention as electrode materials for next-generation rechargeable metal-ion batteries (MIBs), due to their high theoretical capacity, good chemical stability, long lifespan, and natural abundance. In this review, the recent progress of the design and engineering of metal phosphate-based electrode materials for MIBs is summarized. Specifically, the survey will focus on three types of phosphates, monometallic phosphates, bimetallic phosphates, and multi-metal phosphates, within the context of their intrinsic structure and corresponding electrochemical performance. A range of experimental variables will be carefully analyzed, such as sample synthesis, crystal structure, and electrochemical reaction mechanism, in conjunction with theoretical calculations. The applications of these materials as MIB electrodes are then featured for diverse MIBs, such as lithium-ion battery, sodium-ion batteries, potassium-ion batteries, calcium-ion batteries, and magnesium-ion batteries. We conclude the review with a perspective where the promises and challenges of phosphate-based electrodes for MIBs are highlighted, along with future research directions.

Typical layered structures with large capacity have attracted much interest in lithium ion batteries and emerging post-lithium ion batteries. However, these typical layered oxides, including α-, δ-V2O5, δ-MnO2, and α-MoO3, have suffered poor electrical conductivity, severe structural deterioration, and sluggish diffusion kinetics during the repetitive charging/discharging process. In recent years, interlayer engineering of preintercalation strategies has offered effective solutions for solving these problems. Structural water molecules (H2O), monovalent alkali cations (Li+/Na+/K+) and ammonium ion ( NH 4 + ), multivalent alkali-earth cations (Mg2+/Ca2+/Ba2+) and aluminum ion (Al3+), various transition metal cations (Mn2+/Fe2+/Co2+/Ni2+/Cu2+/Zn2+/Ag+, etc.), and organic molecules (PANI/PEDOT/PEO, etc.) have been proved to be efficient “pillars” for stabilizing the fragile layered structure and enhanced diffusion kinetics. These prominent effects have boosted the developments of preintercalated layered structures for emerging multivalent metal-ion batteries, especially rechargeable aqueous zinc ion batteries (AZIBs). In this review, we have clarified the representative crystal structures, preparation methods, advanced characterization methods and corresponding mechanistic insights, and successful applications of these preintercalated layered oxides in multivalent metal-ion batteries.

Two-dimensional (2D) titanium (Ti)-based nanomaterials have been extensively investigated due to their small strain expansion, abundant ion diffusion paths, high safety, and low cost. Nonetheless, such Ti-based nanosheets typically exhibit only poor electrical conductivity and can easily restack. Great efforts have been contributed to alleviating these issues based on nanofabrication and nanoengineering strategies. In this review, we survey the recent progress of the preparation and applications of 2D Ti-based nanostructures in electrochemical energy storage, such as supercapacitors, lithium-ion batteries, sodium-ion batteries, and other multivalent metal-ion batteries, with a focus on the crystal structure, electrochemical energy storage mechanism, and advanced in situ characterization techniques. Finally, a perspective is included to highlight the challenges and promises in the exploitation of 2D Ti-based materials for further enhancement of the performance of energy storage devices.

Niobium (Nb)-based materials show great potential in the field of supercapacitors (SCs) and hybrid ion capacitors (HICs) because of their unique crystal structure, rapid ion diffusion ability, excellent chemical durability, and high safety, although they are rare and expensive. However, pure niobium pentoxide has poor conductivity, so the preparation of composite materials and doped materials can effectively enhance its conductivity, thus improving its rate capability. In this review, we summarize the research advances in Nb-based oxides and composites, niobium nitrides, niobium carbides, niobium selenides, and niobium sulfides in recent years. We compare the effect of crystal structures, synthesis methods, and morphology control on the electrochemical performance of niobium-based materials. The energy storage mechanism of Nb-based materials is discussed through corresponding electrochemical reactions and advanced characterization technologies. In addition, the feasible strategies to improve the electrochemical performance of Nb electrodes are briefly introduced. Finally, the future challenges and outlooks of Nb-based materials in energy storage devices are also discussed.

Improving the performance of advanced energy conversion and storage equipments has always been a key issue in energy research. In recent years, layered double hydroxides (LDHs), especially NiFe-LDHs, have been widely used in catalysts, photoactive materials, acid absorbers, supercapacitors and other fields because of their versatility and high efficiency. In addition, due to its unique layered structure and fascinating characteristics, two-dimensional (2D) NiFe-LDHs materials show excellent performance in various energy conversion and storage fields. This review concentrated on rationally designing of 2D NiFe-LDHs by various methods including co-precipitation method, hydrothermal treat, ion exchange, and electrodeposition method. We describe the morphology and interfacial design of 2D NiFe-LDHs and their composites, among which these 2D materials usually take on nanoscale shapes and they adopt shell-core structure, heterostructure, and others. After that this paper expounds advanced characterization technologies to analyse these materials. This review has summarized their electrochemical energy conversion and storage applications. Finally, the future challenges and prospects of 2D NiFe-LDHs materials in energy storage devices and other fields are summarized.

Under the time theme of the energy crisis and environmental pollution, a great deal of attention has been devoted to the field of supercapacitors (SCs) for relieving this situation. Two-dimensional (2D) materials show great potential in various energy storage fields due to their unique and attractive characteristics. Especially, different types of 2D spinel structured Co-based MCo2O4 (M = Co, Ni, Zn, Cu, Fe, and Mn) materials are supposed to be promising candidates of electrode materials for SCs, which ascribes to their natural abundance and superior electrochemical performances including relatively high electron conductivity, rich electroactive sites, high specific capacitance, and good cycling stability. Moreover, 2D spinel structured Co-based materials can incorporate with other nanomaterials to form various diverse composites such as heterostructures, carbonaceous composites, transition metal oxide (TMO) composites, transition metal hydroxide (TMH) composites, transition metal sulfide (TMS) composites, transition metal phosphide (TMP) composites, and ternary composites, which can deliver satisfactory electrochemical performances. In this review, we highlighted the 2D spinel structured Co-based materials and their composites for SC applications. Finally, the future challenges and outlooks of 2D spinel structured Co-based materials in energy storage devices were also discussed.