A layered structure Ni-based MOF was firstly used as the electrode material for a supercapacitor and exhibited a large specific capacitance of 1127 F g−1 at 0.5 A g−1.

By contrast, sodium is widely distributed and accessible worldwide, offering a low-cost and inexhaustible resource, and has similar electrochemical properties as lithium, making Na-ion batteries (NIBs) the most promising alternative to LIBs, especially for large-scale stationary applications. [4][5][6][7] Cathode materials, mainly including oxides [8][9][10][11] and polyanionic compounds, [12][13][14][15] have been reported to deliver encouraging electrochemical performances for practical applications. Although extensive investigations into anode materials, such as carbonaceous materials, [16][17][18][19] alloys, [20][21][22] oxides, [23][24][25] and organic compounds, [26][27][28] have been performed, most show insufficient performance to match the cathodes well, thus greatly impeding the commercialization of NIBs. Presently, hard carbons (HCs), turbostratic carbon with nanosized parallel/random-aligned graphene sheets with abundant nanopores and defects, are the most intriguing anodes for NIBs due to their good performance. [18,19,29,30] Typically, the sodium-storage behavior in HCs shows two distinct voltage regions: one slope above 0.1 V and one flat plateau below 0.1 V. Although many investigations into Na storage in HCs have been conducted, [18,[31][32][33][34][35][36][37][38][39][40][41][42] the specific Na-insertion mechanisms in the two voltage regions are still controversial.Stevens and Dahn first investigated the sodium-insertion behavior into HCs derived from pyrolytic glucose. [31][32][33] They conducted in situ small-angle X-ray scattering (SAXS)/wideangle X-ray scattering measurements at different sodiation/desodiation states and observed a (002) peak shift of the graphitic interlayer spacing in the high-potential sloping region and a change in the electron density of voids in the low-potential plateau, revealing Na + -ion intercalation inside the turbostratic graphene layers (sloping region) and nanopore filling (plateau region), respectively. Subsequently, similar results were obtained by Komaba et al. using ex situ X-ray diffraction (XRD) and SAXS. [34] The Raman peak of the G-band displayed an obvious shift in the sloping region, while no shift in the plateau region was observed, further manifesting that sodium intercalated between the graphene layers and then filled into nanopores. Then, they performed solid-state 23 Na nuclear magnetic resonance (NMR) analysis to study the state of Na-ion insertion in HCs and corroborated the storage mechanisms. [35] Conversely, Liu and co-workers concluded that Na + ions can intercalate between the graphene layers of HCs with a Hard carbons (HCs) are the most promising candidate anode materials for emerging Na-ion batteries (NIBs). HCs are composed of misaligned graphene sheets with plentiful nanopores and defects, imparting a complex correlation between its structure and sodium-storage behavior. The currently debated mechanism of Na + -ion insertion in HCs hinders the development of high-performance NIBs. In this article, ingenious and reliable strategies a...

Metal–organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li‐ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox‐active 2D copper–benzoquinoid (Cu‐THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu‐THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li‐ion battery cathode with a high reversible capacity (387 mA h g−1), large specific energy density (775 Wh kg−1), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three‐electron redox reaction per coordination unit and one‐electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high‐performance MOF‐based cathode materials for efficient energy storage and conversion.

Lithium–sulfur batteries are regarded as one of the most promising candidates for next‐generation rechargeable batteries. However, the practical application of lithium–sulfur (Li–S) batteries is seriously impeded by the notorious shuttling of soluble polysulfide intermediates, inducing a low utilization of active materials, severe self‐discharge, and thus a poor cycling life, which is particularly severe in high‐sulfur‐loading cathodes. Herein, a polysulfide‐immobilizing polymer is reported to address the shuttling issues. A natural polymer of Gum Arabic (GA) with precise oxygen‐containing functional groups that can induce a strong binding interaction toward lithium polysulfides is deposited onto a conductive support of a carbon nanofiber (CNF) film as a polysulfide shielding interlayer. The as‐obtained CNF–GA composite interlayer can achieve an outstanding performance of a high specific capacity of 880 mA h g−1 and a maintained specific capacity of 827 mA h g−1 after 250 cycles under a sulfur loading of 1.1 mg cm−2. More importantly, high reversible areal capacities of 4.77 and 10.8 mA h cm−2 can be obtained at high sulfur loadings of 6 and even 12 mg cm−2, respectively. The results offer a facile and promising approach to develop viable lithium–sulfur batteries with high sulfur loading and high reversible capacities.

Antimony (Sb)-based anode materials have recently aroused great attention in potassium-ion batteries (KIBs), because of their high theoretical capacities and suitable potassium inserting potentials. Nevertheless, because of large volumetric expansion and severe pulverization during potassiation/depotassiation, the performance of Sb-based anode materials is poor in KIBs. Herein, a composite nanosheet with bismuth–antimony alloy nanoparticles embedded in a porous carbon matrix (BiSb@C) is fabricated by a facile freeze-drying and pyrolysis method. The introduction of carbon and bismuth effectively suppress the stress/strain originated from the volume change during charge/discharge process. Excellent electrochemical performance is achieved as a KIB anode, which delivers a high reversible capacity of 320 mA h g–1 after 600 cycles at 500 mA g–1. In addition, full KIBs by coupling with Prussian Blue cathode deliver a high capacity of 396 mA h g–1 and maintain 360 mA h g–1 after 70 cycles. Importantly, the operando X-ray diffraction investigation reveals a reversible potassiation/depotassiation reaction mechanism of (Bi,Sb) ↔ K­(Bi,Sb) ↔ K3(Bi,Sb) for the BiSb@C composite. Our findings not only propose a reasonable design of high-performance alloy-based anodes in KIBs but also promote the practical use of KIBs in large-scale energy storage.

Bismuth has emerged as a promising anode material for sodium‐ion batteries (SIBs), owing to its high capacity and suitable operating potential. However, large volume changes during alloying/dealloying processes lead to poor cycling performance. Herein, bismuth nanoparticle@carbon (Bi@C) composite is prepared via a facile annealing method using a commercial coordination compound precursor of bismuth citrate. The composite has a uniform structure with Bi nanoparticles embedded within a carbon framework. The nanosized structure ensures a fast kinetics and efficient alleviation of stress/strain caused by the volume change, and the resilient and conductive carbon matrix provides an interconnected electron transportation pathway. The Bi@C composite delivers outstanding sodium‐storage performance with an ultralong cycle life of 30 000 cycles at a high current density of 8 A g−1 and an excellent rate capability of 71% capacity retention at an ultrahigh current rate of 60 A g−1. Even at a high mass loading of 11.5 mg cm−2, a stable reversible capacity of 280 mA h g−1 can be obtained after 200 cycles. More importantly, full SIBs by pairing with a Na3V2(PO4)3 cathode demonstrates superior performance. Combining the facile synthesis and the commercial precursor, the exceptional performance makes the Bi@C composite very promising for practical large‐scale applications.

Layered structure Zn-doped Ni-MOF was first used as the electrode material for a supercapacitor and exhibited a large specific capacitance of 1620 F g−1 at 0.25 A g−1.

Red phosphorus (P) has been recognized as a promising storage material for Li and Na. However, it has not been reported for K storage and the reaction mechanism remains unknown. Herein, a novel nanocomposite anode material is designed and synthesized by anchoring red P nanoparticles on a 3D carbon nanosheet framework for K-ion batteries (KIBs). The red P@CN composite demonstrates a superior electrochemical performance with a high reversible capacity of 655 mA h g at 100 mA g and a good rate capability remaining 323.7 mA h g at 2000 mA g , which outperform reported anode materials for KIBs. The transmission electron microscopy and theoretical calculation results suggest a one-electron reaction mechanism ofP + K + e → KP, corresponding to a theoretical capacity of 843 mA h g ,which is the highest value for anode materials investigated for KIBs. The study not only sheds light on the rational design of high performance red P anodes for KIBs but also offers a fundamental understanding of the potassium storage mechanism of red P.