Defect-Induced Dense Amorphous/Crystalline Heterophase Enables High-Rate and Ultrastable Sodium Storage

Nanoarchitectured Fe3C@N-Doped C/FeVO4 as High-Performance Anode for Sodium-Ion Batteries

Ferric vanadate exhibits potential as an attractive anode material for sodium-ion batteries (SIBs) due to the multiple oxidation states of vanadium and natural abundances of iron. However, the design and fabrication of high-performance ferric vanadate-based SIB anode materials with unique composite nanostructures are still challenging. Herein, a facile self-template method is reported to synthesize 1D nanostructured Fe3C@N-doped C/FeVO4 (Fe3C@NC/FeVO4) anode materials by the combination of morphology regulation with hybrid composite construction, for the first time. To this end, a 1D Fe, N-doped carbon nanotube (FeNC) is used as a template, followed by etching and re-growth to obtain the 1D Fe3C@N-doped C/FeVO4 nanostructure. The introduction of Fe3C can improve its electronic conductivity and enhance capacitive behavior. Additionally, the 1D nanostructure can effectively shorten the ions transport path and alleviate volume expansion during the charge-discharge processes. With these advantages, the SIBs using such anodes show a remarkable rate performance with a capacity of 325.4 mAh g-1 at 0.1 A g-1, 150.6 mAh g-1 at 5 A g-1, and excellent cycling stability with a reversible capacity of 139.6 mAh g-1 at 1 A g-1 after 1500 cycles. This work offers a new strategy for the future development of SIBs with ferric vanadate-based anode.

Oxalate-derived porous C-doped NiO with amorphous-crystalline heterophase for supercapacitors

Constructing amorphous/crystalline heterophase structure with high porosity is a promising strategy to effectively tailor the physicochemical properties of electrode materials and further improve the electrochemical performance of supercapacitors. Here, the porous C-doped NiO (C-NiO) with amorphous/crystalline heterophase grown on NF was prepared using NF as Ni source via a self-sacrificial template method. Calcining the self-sacrificial NiC2O4 template at a suitable temperature (400 °C) was beneficial to the formation of porous heterophase structure with abundant cavities and cracks, resulting in high electrical conductivity and rich ion/electron-transport channels. The density functional theory (DFT) calculations further verified that in-situ C-doping could modulate the electronic structure and enhance the OH- adsorption capability. The unique porous amorphous/crystalline heterophase structure greatly accelerated electrons/ions transfer and Faradaic reaction kinetic, which effectively improved the charge storage. The C-NiO calcined at 400 °C (C-NiO(400)) displayed a markedly enhanced specific charge, outstanding rate property and excellent cycling stability. Furthermore, the hybrid supercapacitor assembled by C-NiO(400) and active carbon achieved a high energy density of 49.0 Wh kg-1 at 800 W kg-1 and excellent cycle stability (90.9 % retention at 5 A/g after 10 000 cycles). This work provided a new strategy for designing amorphous/crystalline heterophase electrode materials in high-performance energy storage.

Amorphous MnRuOx Containing Microcrystalline for Enhanced Acidic Oxygen-Evolution Activity and Stability

Compared to Ir, Ru-based catalysts often exhibited higher activity but suffered significant and rapid activity loss during the challenging oxygen evolution reaction (OER) in a corrosive acidic environment. Herein, we developed a hybrid MnRuOx catalyst in which the RuO2 microcrystalline regions serve as a supporting framework, and the amorphous MnRuOx phase fills the microcrystalline interstices. In particular, the MnRuOx-300 catalyst from an annealing temperature of 300 °C contains an optimal amorphous/crystalline heterostructure, providing substantial defects and active sites, facilitating efficient adsorption and conversion of OH-. In addition, the heterostructure leads to a relative increase of the d-band center close to the Fermin level, thus accelerating electron transfer with reduced charge transfer resistance at the active interface between crystalline and amorphous phases during the OER. The catalyst was further thoroughly evaluated under various operating conditions and demonstrated exceptional activity and stability for the OER, representing a promising solution to replace Ir in water electrolyzers.

Al-Based MOF-Derived Amorphous/Crystalline Heterophase Cobalt Sulfides as High-Performance Supercapacitor Materials

Transition metal sulfides (TMSs) are promising electrode materials due to their high theoretical specific capacitance, but sluggish charge transfer kinetics and an insufficient number of active sites hamper their applications in supercapacitors. In this work, a self-sacrificial template strategy was employed to construct Al-based MOF-derived metal sulfides with an amorphous/crystalline (a/c) heterophase, in which aluminum, nitrogen, and carbon species were evenly coordinated in the amorphous phase. The metal sulfides a/c-Co(Al)S-1 and a/c-Co(Al)S-2, originating from the CAU-1 and CoAl-MOF on NF as self-sacrificial templates, were investigated as electrode materials, respectively, in which the a/c-Co(Al)S-1 showed a more excellent electrochemical performance. Through acid etching CAU-1 using Co(NO3)2 followed by sulfuration, the a/c-Co(Al)S-1 with a unique 3D network structure was constructed, whose unique architecture expanded the interfacial contact with the electrolyte and provided vast active sites, accelerating the charge transportation and ion diffusion. Notably, the a/c-Co(Al)S-1 displayed a high specific charge of 1791.8 C g-1 at 1 A g-1, satisfactory cycle stability, and good rate capability. The corresponding assembled a/c-Co(Al)S-1//AC device delivered a high energy density of 77.1 Wh kg-1 at 800 W kg-1 and good durability (87.4% capacitance retention over 10 000 cycles).

One-step Solid-State Synthesis of V1.13Se2/V2O3 Heterostructure as a High Pseudocapacitance Anode for Fast-Charging Sodium-Ion Batteries

Sodium-ion batteries (SIBs) offer several benefits, including cost-efficiency and fast-charging characteristics, positioning them as attractive substitutes for lithium-ion batteries in energy storage applications. However, the inferior capacity and cycling stability of electrodes in SIBs necessitate further enhancement due to sluggish reaction kinetics. In this respect, the utilization of heterostructures, which can provide an inherent electric field and abundant active sites on the surface, has emerged as a promising strategy for augmenting the cycling stability and rate features of the electrodes. This work delves into the utilization of V1.13Se2/V2O3 heterostructure materials as anodes, initially fabricated via a simplified one-step solid-state sintering technique. The high pseudocapacitance and low characteristic relaxation time constant give the V1.13Se2/V2O3 heterostructure impressive properties, such as a high capacity of 328.5 mAh g-1 even after 1500 cycles at a high current density of 2 A g-1 and rate capability of 278.9 mAh g-1 at 5 A g-1. Moreover, the assembled sodium-ion full battery delivers a capacity of 118.5 mAh g-1 after 1000 cycles at 1 A g-1. These findings provide novel insight and guidance for the rapid synthesis of heterojunction materials and the advancement of SIBs.

Amorphous Modulation of Atomic Nb-O/N Clusters with Asymmetric Coordination in Carbon Shells for Advanced Sodium-Ion Hybrid Capacitors

Anode materials with excellent properties have become the key to develop sodium-ion hybrid capacitors (SIHCs) that combine the advantages of both batteries and capacitors. Amorphous modulation is an effective strategy to realize high energy/power density in SIHCs. Herein, atomically amorphous Nb-O/N clusters with asymmetric coordination are in situ created in N-doped hollow carbon shells (Nb-O/N@C). The amorphous clusters with asymmetric Nb-O3/N1 configurations have abundant charge density and low diffusion energy barriers, which effectively modulate the charge transport paths and improve the reaction kinetics. The clusters are also enriched with unsaturated vacancy defects and isotropic ion-transport channels, and their atomic disordering exhibits high structural stress buffering, which are strong impetuses for realizing bulk-phase-indifferent ion storage and enhancing the storage properties of the composite. Based on these features, Nb-O/N@C achieves notably improved sodium-ion storage properties (reversible capacity of 240.1 mAh g-1 at 10.0 A g-1 after 8000 cycles), and has great potential for SIHCs (230 Wh Kg-1 at 4001.5 W Kg-1). This study sheds new light on developing high-performance electrodes for sodium-ion batteries and SIHCs by designing amorphous clusters and asymmetric coordination.

The synthesis and application of crystalline-amorphous hybrid materials

Crystalline-amorphous hybrid materials (CA-HMs) possess the merits of both pure crystalline and amorphous phases. Abundant dangling bonds, unsaturated coordination atoms, and isotropic structural features in the amorphous phase, as well as relatively high electronic conductivity and thermodynamic structural stability of the crystalline phase simultaneously take effect in CA-HMs. Furthermore, the atomic and bandgap mismatch at the CA-HM interface can introduce more defects as extra active sites, reservoirs for promoted catalytic and electrochemical performance, and induce built-in electric field for facile charge carrier transport. Motivated by these intriguing features, herein, we provide a comprehensive overview of CA-HMs on various aspects-from synthetic methods to multiple applications. Typical characteristics of CA-HMs are discussed at the beginning, followed by representative synthetic strategies of CA-HMs, including hydrothermal/solvothermal methods, deposition techniques, thermal adjustment, and templating methods. Diverse applications of CA-HMs, such as electrocatalysis, batteries, supercapacitors, mechanics, optoelectronics, and thermoelectrics along with underlying structure-property mechanisms are carefully elucidated. Finally, challenges and perspectives of CA-HMs are proposed with an aim to provide insights into the future development of CA-HMs.

Synergistically Designed Dual Interfaces to Enhance the Electrochemical Performance of MoO2 /MoS2 in Na- and Li-Ion Batteries

It is indispensable to develop and design high capacity, high rate performance, long cycling life, and low-cost electrodes materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, MoO₂ /MoS₂ /C, with dual heterogeneous interfaces, is designed to induce a built-in electric field, which has been proved by experiments and theoretical calculation can accelerate electrochemical reaction kinetics and generate interfacial interactions to strengthen structural stability. The carbon foam serves as a conductive frame to assist the movement of electrons/ions, as well as forms heterogeneous interfaces with MoO₂ /MoS₂ through CS and CO bonds, maintaining structural integrity and enhancing electronic transport. Thanks to these unique characteristics, the MoO₂ /MoS₂ /C renders a significantly enhanced electrochemical performance (324 mAh g^-1 at 1 A g^-1 after 1000 cycles for SIB and 500 mAh g^-1 at 1 A g^-1 after 500 cycles for LIBs). The current work presents a simple, useful and cost-effective route to design high-quality electrodes via interfacial engineering.

Origin of oxygen-redox and transition metals dissolution in Ni-rich LixNi0.8Co0.1Mn0.1O2 cathode

Recently, Ni-rich LiNi_xCo_yMn_1-x-yO₂ (x ≥ 0.8) draw significant research attention as cathode materials in lithium-ion batteries due to their superiority in energy density. However, the oxygen release and the transition metals (TMs) dissolution during the (dis)charging process lead to serious safety issues and capacity loss, which highly prevent its application. In this work, we systematically explored the stability of lattice oxygen and TM sites in LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) cathode via investigating various vacancy formations during lithiation/delithiation, and properties such as the number of unpaired spins (NUS), net charges, and d band center were comprehensively studied. In the process of delithiation (x = 1 → 0.75 → 0), the vacancy formation energy of lattice oxygen [E_vac(O)] has been identified to follow the order of E_vac(O-Mn) > E_vac(O-Co) > E_vac(O-Ni), and E_vac(TMs) shows a consistent trend with the sequence of E_vac(Mn) > E_vac(Co) > E_vac(Ni), demonstrating the importance of Mn to stabilize the structural skeleton. Furthermore, the |NUS| and net charge are proved to be good descriptors for measuring E_vac(O/TMs), which show linear correlations with E_vac(O) and E_vac(TMs), respectively. Li vacancy plays a pivotal role on E_vac(O/TMs). E_vac(O/TMs) at x = 0.75 vary extremely between the NiCoMnO layer (NCM layer) and the NiO layer (Ni layer), which correlates well with |NUS| and net charge in the NCM layer but aggregates in a small region in the Ni layer due to the effect of Li vacancies. In general, this work provides an in-depth understanding of the instability of lattice oxygen and transition metal sites on the (104) surface of Ni-rich NCM811, which might give new insights into oxygen release and transition metal dissolution in this system.

Kinetics-Driven MnO2 Nanoflowers Supported by Interconnected Porous Hollow Carbon Spheres for Zinc-Ion Batteries

For rechargeable aqueous zinc-ion batteries (ZIBs), manganese dioxide is one of the most promising candidates as a cathode material because of its cost effectiveness, eco-friendliness, and high specific capacities. However, the ZIBs suffer from poor rate performance and low cycle life due to the weak intrinsic electronic conductivity of manganese dioxide, poor ion diffusion of lump manganese dioxide, and its volumetric expansion during the cycle. Herein, we prepare MnO₂@carbon composites (MnO₂@IPHCSs) by in situ growing MnO₂ nanoflowers on an interconnected porous hollow carbon spheres (IPHCSs) template. IPHCSs, as excellent conductors, significantly improve the conductivity of the manganese dioxide cathode. The hollow porous carbon framework of IPHCSs can offer more ion diffusion paths to internal MnO₂@IPHCS carbon composites and acts as a buffer room to cope with the drastic volume contraction and expansion during charge/discharge cycling. The rate performance tests show that MnO₂@IPHCSs with high conductivity have a specific capacity of 147 mA h g^-1 at 3 C. MnO₂@IPHCSs with hollow and nanoflower structures are shown to have excellent ion diffusion performance (ion diffusion coefficient = 10^-11 to 10^-10 cm² s^-1) in the electrochemical kinetics of the galvanostatic intermittent titration technique. Long cycle performance testing and in situ Raman characterization reveal that MnO₂@IPHCSs have high cycling stability (85.5% capacity retention after 800 cycles) and reversibility due to the enhanced structure and increased conductivity. The excellently conductive manganese dioxide supported by IPHCSs has good rate and cycling performance, which can be used to produce superior-performance ZIBs.