The intercalation of potassium ions into graphite is demonstrated to be feasible, while the electrochemical performance of potassium-ion batteries (KIBs) remains unsatisfying. More effort is needed to improve the specific capacity while maintaining a superior rate capability. As an attempt, nitrogen/oxygen dual-doped hierarchical porous hard carbon (NOHPHC) is introduced as the anode in KIBs by carbonizing and acidizing the NH -MIL-101(Al) precursor. Specifically, the NOHPHC electrode delivers high reversible capacities of 365 and 118 mA h g at 25 and 3000 mA g , respectively. The capacity retention reaches 69.5% at 1050 mA g for 1100 cycles. The reasons for the enhanced electrochemical performance, such as the high capacity, good cycling stability, and superior rate capability, are analyzed qualitatively and quantitatively. Quantitative analysis reveals that mixed mechanisms, including capacitance and diffusion, account for the K-ion storage, in which the capacitance plays a more important role. Specifically, the enhanced interlayer spacing (0.39 nm) enables the intercalation of large K ions, while the high specific surface area of ≈1030 m g and the dual-heteroatom doping (N and O) are conducive to the reversible adsorption of K ions.

Novel and complex mesoporous 2D and 3D architectures of the oxide semiconductor Co(3)O(4), including nanosheets, nearly monodisperse microspheres that are self-assembled from nanosheets, and copper-coin-like nanosheets, have been synthesized through a facile binary-solution route and sequential thermal decomposition at atmospheric pressure. The influence of different reaction conditions on the morphology of the products has been discussed in detail. The results revealed that the volume ratio of H(2)O and ethanolamine (EA) play a crucial role in the morphology of the precursor. The thermal decomposition of the corresponding precursor leads to the formation of the mesoporous structure. The products have been characterized by X-ray diffraction techniques, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy. The electrochemical properties of the Co(3)O(4) electrodes were investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The electrochemical experiments revealed that the specific capacitance of the Co(3)O(4) nanosheets was higher than that of the Co(3)O(4) microspheres in a KOH electrolyte solution (3 m). Furthermore, the Co(3)O(4) nanosheet electrodes exhibited good rate capabilities, and maintained 93% of the initial capacity at a current density of 5 mA cm(-2) in a KOH (3 m) electrolyte solution. The results show that Co(3)O(4) nanosheets might have potential applications as electrode materials for supercapacitors.

Dendrite growth of metal anodes is one of the key hindrances for both secondary aqueous metal batteries and nonaqueous metal batteries. In this work, a freestanding Ti3C2T x MXene@Zn paper is designed as both zinc metal anode and lithium metal anode host to address the issue. The binder-free Ti3C2T x MXene@Zn paper exhibits merits of good mechanical flexibility, high electronic conductivity, hydrophilicity, and lithiophilicity. The crystal growth mechanism of Zn metal on common Zn foil and Ti3C2T x MXene@Zn composite is also studied. It is found that the Ti3C2T x MXene@Zn paper can effectively suppress the dendrite growth of Zn, enabling reversible and fast Zn plating/stripping kinetics in an aqueous electrolyte. Moreover, the Ti3C2T x MXene@Zn paper can be used as a 3D host for a lithium metal anode. In this host, Zn is utilized as a nucleation agent to suppress the Li dendrite growth. The freestanding Ti3C2T x MXene@Zn@Li anode exhibits superior reversibility with high Coulombic efficiency (97.69% over 600 cycles at 1.0 mA cm–2) and low polarization compared with the Cu@Li anode. These findings may be useful for the design of dendrite-free metal-based energy storage systems.

The first synthesis of MnO@Mn O nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn O /NPCF) through pyrolysis of mixed-valent Mn clusters is reported. The unique features of MnO@Mn O /NPCF are derived from the distinct interfacial structure of the Mn clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn O are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn O , the uniform distribution, and the NPCF, MnO@Mn O /NPCF displays unprecedented lithium-storage performance (1500 mA h g at 0.2 A g over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn O and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

Despite the desirable advancement in synthesizing transition-metal phosphides (TMPs)-based hybrid structures, most methods depend on foreign-template-based multistep procedures for tailoring the specific structure. Herein, a self-template and recrystallization-self-assembly strategy for the one-step synthesis of core-shell-like cobalt phosphide (CoP) nanoparticles embedded into nitrogen and phosphorus codoped porous carbon sheets (CoP⊂NPPCS), is first proposed. Relying on the unusual coordination ability of melamine with metal ions and the cooperative hydrogen bonding of melamine and phytic acid to form a 2D network, a self-synthesized single precursor can be attained. Importantly, this approach can be easily expanded to synthesize other TMPs⊂NPPCS. Due to the unique compositional and structural characteristics, these CoP⊂NPPCSs manifest outstanding electrochemical performances as anode materials for both lithium- and potassium-ion batteries. The unusual hybrid architecture, the high specific surface area, and porous features make the CoP⊂NPPCS attractive for other potential applications, such as supercapacitors and electrocatalysis.

Lithium–sulfur batteries (LSBs) with a high theoretical capacity of 1675 mAh g−1 hold promise in the realm of high‐energy‐density Li–metal batteries. To cope with the shuttle effect and sluggish transformation of soluble lithium polysulfides (LiPSs), varieties of traditional metal‐based materials (such as metal, metal oxides, metal sulfides, metal nitrides, and metal carbides) with unique catalytic activity for accelerating LiPSs redox have been exploited to fundamentally inhibit the shuttle effect and improve the performance of LSBs. Concurrently, some budding catalytic materials also possess enormous potential for facilitating LiPSs redox reaction in LSBs, including metal borides, metal phosphides, metal selenides, single atoms, and defect‐engineered materials. Here, recent advances in these emerging catalytic candidates as well as the evaluation methods and parameters for catalytic materials are comprehensively summarized for the first time. New insights are also given to aid in the design of high‐performance LSBs and satisfy the high expectation in the future, including the exposure of the active sites and adsorption‐catalysis synergy strategies. Finally, the current challenges and prospects for designing highly efficient catalytic materials are highlighted, aiming at providing guidance for configuring catalytic materials to make sure high‐energy and long‐life LSBs.

Sodium-ion batteries (SIBs) are considered promising next-generation energy storage devices. However, a lack of appropriate high-performance anode materials has prevented further improvements. Here, a hierarchical porous hybrid nanosheet composed of interconnected uniform TiO nanoparticles and nitrogen-doped graphene layer networks (TiO @NFG HPHNSs) that are synthesized using dual-functional C N nanosheets as both the self-sacrificing template and hybrid carbon source is reported. These HPHNSs deliver high reversible capacities of 146 mA h g at 5 C for 8000 cycles, 129 mA h g at 10 C for 20 000 cycles, and 116 mA h g at 20 C for 10 000 cycles, as well as an ultrahigh rate capability up to 60 C with a capacity of 101 mA h g . These results demonstrate the longest cyclabilities and best rate capability ever reported for TiO -based anode materials for SIBs. The unprecedented sodium storage performance of the TiO @NFG HPHNSs is due to their unique composition and hierarchical porous 2D structure.

Rechargeable aqueous zinc-ion batteries (AZIBs) have captured a surge of interest in recent years as a promising alternative for scalable energy storage applications owing to the intrinsic safety, affordability, environmental benignity, and impressive electrochemical performance. Despite the facilitated development of this technology by many investigations, however, its smooth implementation is still plagued by inadequate energy density and undesirable life span, which calls for an efficient and controllable cathode storage chemistry. Here, this review focuses on the key bottlenecks by offering a comprehensive summary of representative cathode materials and comparatively analyzing their structural features and electrochemical properties. Then, we critically present several feasible electrode design strategies to guide future research activities from a fundamental perspective for high-energy-density and durable cathode materials mainly in terms of interlayer regulation, defect engineering, multiple redox reactions, activated two-electron reactions, and electrochemical activation and conversion. Finally, we outline the remaining challenges and future perspectives of developing high-performance AZIBs.