Poor Electronic Conductivity Research Articles

Double carbon modified Na3V2(PO4)3 with dual charge carriers and high performance synthesized in-situ in polypyrrole and chitosan quaternary ammonium hydrogel

Sodium-ion batteries (SIBs) are regarded as the most promising battery to replace lithium-ion batteries (LIBs) in the future. Na3V2(PO4)3 (NVP), as an ideal positive electrode material for SIBs, is limited by poor electronic conductivity and low reversible capacity. In this paper, the double carbon resources of chitosan quaternary ammonium hydrogel (CHACC) and Polypyrrole (PPy) were introduced into NVP. Through the construction of double charge carriers, the high conductivity and the high reversible capacity of NVP which broke the theoretical limit were achieved. The introduction of CHACC brings the second charge carrier, ClO4−, in addition to Na+ in NVP system. Furthermore, the conductive network and defect-rich carbon coatings formed by CHACC and PPy significantly improve the electronic conductivity and kinetics of the electrode. Comprehensively, the detailed functional mechanism of dual carriers in NVP is deeply investigated by ex-situ FTIR and XPS, revealing that ClO4− utilizes the N+ in the carbonized substrate of CHACC and PPy as the binding sites to reversibly inserted/extracted from the carbon layer to provide additional capacities. Notably, the optimized CHACC-PPy-NVP submits superior sodium storage performance. It delivers a capacity of 148.3 and 139.3 mAh g−1 at 0.1 and 1C, significantly exceeding the theoretical capacity (117.6 mAh g−1). Even at 140C, it still maintains a capacity value of 88.9 mAh g−1 with 75.7 mAh g−1 remaining after 2000 cycles, corresponding to a low decay rate of 0.007 % per cycle.

Fabrication of Highly Conductive Porous Fe3O4@RGO/PEDOT:PSS Composite Films via Acid Post-Treatment and Their Applications as Electrochemical Supercapacitor and Thermoelectric Material.

As a remarkable multifunctional material, ferroferric oxide (Fe3O4) exhibits considerable potential for applications in many fields, such as energy storage and conversion technologies. However, the poor electronic and ionic conductivities of classical Fe3O4 restricts its application. To address this challenge, Fe3O4 nanoparticles are combined with graphene oxide (GO) via a typical hydrothermal method, followed by a conductive wrapping using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic sulfonate) (PEDOT:PSS) for the fabrication of composite films. Upon acid treatment, a highly conductive porous Fe3O4@RGO/PEDOT:PSS hybrid is successfully constructed, and each component exerts its action that effectively facilitates the electron transfer and subsequent performance improvement. Specifically, the Fe3O4@RGO/PEDOT:PSS porous film achieves a high specific capacitance of 244.7 F g-1 at a current of 1 A g-1. Furthermore, due to the facial fabrication of the highly conductive networks, the free-standing film exhibits potential advantages in flexible thermoelectric (TE) materials. Notably, such a hybrid film shows a high electric conductivity (σ) of 507.56 S cm-1, a three times greater value than the Fe3O4@RGO component, and achieves an optimized Seebeck coefficient (S) of 13.29 μV K-1 at room temperature. This work provides a novel route for the synthesis of Fe3O4@RGO/PEDOT:PSS multifunctional films that possess promising applications in energy storage and conversion.

Synthesis of Ta2O5 by introducing graphene quantum dot with excellent photocatalytic performance for degradation of tetracycline

Wide band gap, weak adsorption ability, poor electronic conductivity and insufficient charge transportation limit the applications of Ta2O5 in photodegradation of antibiotics. The paper reports synthesis of Ta2O5 photocatalyst by introducing glycine-functionalized graphene quantum dot (GGQD). The introduction of GGQD effectively prevents the hydrolysis of Ta(V) and finally leads to the formation of small Ta2O5 nanorods. The modification of graphene sheets on the Ta2O5 surface enhances the adsorption towards tetracycline. The presence of Ta4+ self-doped oxygen vacancy narrows the band gap of Ta2O5, optimizes the band position and creates new defect energy level. These improve the light absorption capacity to visible light and promotes the photogenerated charge transfer. The graphene as electron trap suppresses the recombination of photogenerated charge carriers. The graphene as light sensitizer expands the absorption to visible light. The synergy of these multiple structure engineering realizes an excellent photocatalytic performance of Ta2O5 for solar-light driven tetracycline photodegradation. The photodegradation efficiency of 60 min solar-light irradiation is 6.6 times higher, apparent kinetic constant is 19.3 times higher and photocurrent density is 13.4 times over Ta2O5. The study also paves an avenue for construction of metal nanomaterials with desirable photoelectric properties in catalysis, energy storage and conversion and sensing.

Spontaneously dissolved MnO: A better cathode material for rechargeable aqueous zinc-manganese batteries

Manganese-based oxides (MnOx) cathodes, with profuse crystal structures and valence states, have raised extensive research interstate for aqueous zinc-manganese batteries. However, the lack of a clear reaction mechanism and source of capacity presents significant challenges for the design and development of advanced manganese-based oxide cathodes. Herein, by exploring the electrochemical activation processes and reaction mechanisms of MnOx (including MnO2, Mn2O3, Mn3O4 and MnO), MnO is proved to hold superior potential for zinc-ion batteries cathode application compared to other MnOx owing to its exceptional spontaneous dissolution activation activity and the largest proportion of Mn. Further, to ulteriorly enhance the dissolution activation and poor electronic conductivity of MnO, a porous carbon matrix-encapsulated MnO nanocomposite (MnO@PC) is successfully synthesized. Moreover, the porous carbon matrix could facilitate electrolyte infiltration and promote adsorption towards Mn2+ and Zn2+ cations, leading to more Zn4SO4·(OH)6·xH2O (ZSH) deposition and greater stability of the reversible ZSH-assisted deposition/dissolution reaction. Therefore, MnO@PC can display improved capacity of 269 mAh g-1 (0.1 A g-1) with an exceptional capacity retention of 93% after 120 cycles in pure ZnSO4 electrolyte. And at 2.0 A g-1, the capacity could reach 75 mAh g-1 and be well maintained in 2000 cycles.

Synthesized Fe-doped Co3O4 nanoparticles-based anode for high-performance lithium-ion batteries application

ABSTRACT Co3O4 has been considered a promising anode material because of its high theoretical capacity (890 mAh/g) and remarkable energy density. Unfortunately, it suffers from low initial coulombic efficiency, rapid capacity fading, poor electronic conductivity, large volume changes, and aggregation during the lithium ion intercalation/deintercalation process. In this work, a series of Fe2+-doped Co3O4 nanostructured materials Co3(1-x)Fe3xO4 (x = 0, 0.01, 0.02 and 0.03) were produced by a simple chemical co-precipitation method. The Fe doping led to a slight increase of the lattice parameter, which is beneficial to the rapid diffusion of Li+ ion during the lithiation/delithiation process. Meanwhile, the Fe-doped Co3O4 sample exhibited an excellent rate capability of 886.47 mAh/g at 500 mA/g, and outstanding cyclic stability (1156.91 mAh/g for 50 cycles, with the capacity retention rate of 83.53% at the current density of 100 mA/g), demonstrating improved electrochemical performance, compared with that of pure Co3O4. The good electrochemical performance profited from the formation of oxygen vacancies by Fe doping, which provided more space for Li+ diffusion and improved the electronic conductivity of the anode material. This work provides a simple way to improve the comprehensive electrochemical performance of the transitional metal oxide Co3O4 anode electrodes for lithium-ion batteries.

Rational design of hollow Ti2Nb10O29 nanospheres towards High-Performance pseudocapacitive Lithium-Ion storage

Ti2Nb10O29, as one of the most promising anode materials for lithium-ion batteries (LIBs), possesses excellent structural stability during lithiation/delithiation cycling and higher theoretical capacity. However, Ti2Nb10O29 faces some challenges, such as insufficient ion diffusion coefficient and poor electronic conductivity. To overcome these problems, this study investigates the effect of applying nanostructure engineering on Ti2Nb10O29 and the lithium storage behaviors. We successfully synthesized hollow Ti2Nb10O29 nanospheres (h-TNO NSs) via solvothermal method using phenolic resin nanospheres as the template. The effects of using a template or not and the annealing atmospheres on the microstructures of the as-prepared Ti2Nb10O29 are investigated. Different nanostructures (porous Ti2Nb10O29 nanoaggregates (p-TNO NAs) without a template and core-shelled Ti2Nb10O29@C nanospheres (cs-TNO@C NSs)) were formed through annealing in Ar. When examined as anodes for LIBs, the h-TNO NSs electrode with hollow spherical structure displayed a better lithium storage performance. Compared to its counterparts, p-TNO NAs and cs-TNO@C NSs, h-TNO NSs electrode exhibited a higher reversible capacity of 282.5 mAh g−1 at 1C, capacity retention of 79.5% (i.e., 224.6 mAh g−1) after 200 cycles, and a higher rate capacity of 173.1 mAh g−1 at 10C after 600 cycles. The excellent electrochemical performance of h-TNO NSs is attributed to the novel structure. The hollow nanospheres with cavities and thin shells not only exposed more active sites and improved ion diffusion, but also buffered the volume variation upon cycling and facilitated electrolyte penetration. This consequently enhanced the lithium storage performance of the electrode and its high pseudocapacitive contribution (90% at 1.0 mV s−1).

Construction of high-rate performance sulfurized Poly(acrylonitrile) nanofibers cathodes for practical lithium–sulfur batteries via tellurium catalytic regulation

The rapid charge-discharge and wide operating temperature range are of great significance to the research of lithium-sulfur batteries. However, the poor electronic and ionic conductivity of sulfurized polyacrylonitrile limits the high-rate and low-temperature performance of lithium-sulfur batteries. In this work, a tellurium-doped sulfurized polyacrylonitrile nanofibers-based cathode material (Te0.02S0.98FPAN) is successfully fabricated by air-blow spinning for lithium-sulfur batteries. It is found that Te0.02S0.98FPAN maintained a high reversible specific capacity of 742 mAh·g−1composites after 200 cycles at a current density of 0.2 C (0.014% decay per cycle), whereas it provides a reversible specific capacity of 641 mAh·g−1composites after 500 cycles even at a large current density of 1.0 C (0.021% decay per cycle), manifesting its excellent high-rate performance. Moreover, Te0.02S0.98FPAN still maintained a high reversible specific discharge capacity of 586 mAh·g−1composites after 100 cycles at 0.2 C at a low temperature of 5.0 °C, confirming its wide operating temperature range. Both the eutectic accelerator (tellurium) and the one-dimensional nanofibrous structure greatly improve the migration rate and electron transport ability of Li+ ions, enhancing reaction kinetics and providing fast and stable migration channels for ions and electrons. Therefore, Te0.02S0.98FPAN has a higher oxidation-reduction reaction rate and less polarization. This study not only provides new ideas for the cathode design of lithium-sulfur batteries with high rate and wide temperature range, but also paves the way for the development of practical lithium-sulfur batteries. In particular, when tested in practical conditions of high areal loading (Te0.02S0.98: 5.0 mg cm−2) and lean electrolyte (E/Te0.02S0.98: 10 μL mg−1), this cathode delivers high reversible capacities of 725 mAh g−1 composite (0.1 C) and 663 mAh g−1 composite (0.2 C), demonstrating its great potential for future application.

Tailored voltage plateau enabling superior sodium storage for Fe-based fluorophosphate cathode

Iron-based fluorophosphate (NFPF) is the most promising cathode materials integrating cost efficiency and voltage advantages. However, undesirable electrochemical performance is limited by poor electron conductivity and diffusion kinetics as well as ambiguous mechanism of plateau behavior. The article investigates the optimization of the voltage plateau mediated by local structure through Zr modification. In-depth experiment and theoretical calculations reveal that the heteroatom excites electrochemical Na activity and induces broadened Na+ pathway with the embellishment of intrinsic conductivity and highly stable framework. On the grounds of co-facilitation on electrons and ions, the first plateau is significantly extended and its proportion is increased, which liberates the confinement on electrochemical performance. The NFPF-0.07Zr sample maintains capacity of 73.78 mAh g − 1 at 5 C with capacity retention of 68.67% and only 0.02% degradation per cycle over 2000 cycles. The sodium storage mechanism of the dual-biphase reaction is revealed by in situ XRD with slight volume change (3.48%). The assembled full cell outputs initial energy density of 222.3 Wh kg−1 based on the total electrode mass, enabling 150 stable cycles at 1 C. Such a fundamental understanding of the intrinsic mechanism of voltage plateaus offers a rational perspective for designing Fe-based fluorophosphate cathode.

Superior electrochemical performance of self-assemble carbon layer dual-phase TiO2/Zn2Ti3O8 for Li-ion anode

The application of commercial TiO2 (c-TiO2) as the anode material in Li-ion batteries suffers from the poor ionic and electronic conductivities. Herein, Zn2Ti3O8/TiO2 composite was prepared by sintering the mixture of Zn(NO3)2 and commercial TiO2 with various Zn/Ti ratios, so as to introduce Zn2Ti3O8 with Li+ diffusion paths and create additional interfaces for Li+ migration and capacitive energy-storage. Then the composite was self-assembled with the carbon derived from citric acid (CA) to alleviate electronic conductivity. The carbon-coated Zn2Ti3O8/TiO2 composite delivers high charge/discharge capacities of 294.4/298.2 mAh g−1 at 0.1 A g−1 and a reversible capacity of 226.4 mAh g−1 after 1000 cycles at 0.5 A g−1. This work provides a new strategy for the application of c-TiO2 in Li-ion anode.

In-situ constructing pearl necklace-shaped heterostructure: Zn2+ substituted Na3V2(PO4)3 attached on carbon nano fibers with high performance for half and full Na ion cells

Na3V2(PO4)3 (NVP) emerges as prospective cathode for sodium ion batteries. However, the poor electronic and ionic conductivity hinders its development. Traditional synthesis methods only allow ex-situ bonding between the NVP grains and carbon-based substrate, leading to unstable combination. Herein, a simultaneous modification strategy to optimize the morphological features and crystal construction of NVP system is proposed. The in-situ synthesized framework consisting of NVP and high conductive carbon nano fibers (CNFs) can efficiently elevate the electrochemical performance. A distinctive pearl necklace-shaped heterostructure is successfully constructed by electrospinning and carbon-thermal reduction routes. The necklace substrate is derived from the CNFs, possessing the unique unidimensional morphology and bridging well with each other to build a high conductive network. The Zn2+-substituted NVP grains with nano size are grown on the surface of the substrate. The shortened size provides short pathway for Na+ migration, resulting in the improved kinetic characteristics. Furthermore, the substitution of Zn2+ generates p-type doping to introduce favorable hole carriers, enhancing the ionic conductivity. The reduced band gap and migration energy barrier of Na+ for Zn2+ doped NVP is demonstrated by DFT calculations. Accordingly, the modified Zn0.07-ES-800 sample releases a high capacity of 117.5 mA h g−1 at 0.1C. It delivers a capacity of 92.3 mA h g−1 at 100C and maintains 72.7 mA h g−1 after 1000 cycles. Moreover, the Zn0.07-ES-800//Zn0.07-ES-800 full cell shows a high capacity of 94.4 mA h g−1 at 0.1C and keeps 80 mA h g−1 at 1C with a high retention of 95% after 70 cycles.

Cascade Defluorination of Perfluoroalkylated Catholytes Unlocks High Lithium Primary Battery Capacities

AbstractExceeding the energy density of lithium−carbon monofluoride (Li−CFx), today's leading Li primary battery, requires an increase in fluorine content (x) that determines the theoretical capacity available from C−F bond reduction. However, high F‐content carbon materials face challenges such as poor electronic conductivity, low reduction potentials (<1.3 V versus Li/Li+), and/or low C−F bond utilization. This study investigates molecular structural design principles for a new class of high F‐content fluoroalkyl‐aromatic catholytes that address these challenges. A polarizable conjugated system—an aromatic ring with an alkene linker—functions as electron acceptor and redox initiator, enabling a cascade defluorination of an adjacent perfluoroalkyl chain (RF = −CnF2n+1). The synthesized molecules successfully overcome premature deactivation observed in previously studied catholytes and achieve close‐to‐full defluorination (up to 15/17 available F), yielding high gravimetric capacities of 748 mAh g−1fluoroalkyl‐aromatic and energies of 1785 Wh kg−1fluoroalkyl‐aromatic. The voltage compatibility between fluoroalkyl‐aromatics and CFx enables design of hybrid cells containing C−F redox activity in both solid and liquid phases, with a projected enhancement of Li–CFx gravimetric energy by 35% based on weight of electrodes+electrolyte. With further improvement of cathode architecture, these “liquid CFx” analogues are strong candidates for exceeding the energy limitations of today's primary chemistries.

In-situ CNT-loaded organic cathodes for sulfide all-solid-state Li metal batteries

Organic cathodes show promising advantages of extensive resources, high theoretical specific capacity, and mild synthesis conditions, etc., but suffer from low density, poor electronic conductivity, and high solubility in liquid electrolytes. Herein, an in-situ coating method is developed to overcome the above issues by realizing high-performance sulfide all-solid-state batteries with organic Li4C8H2O6 cathode. Li4C8H2O6 composite cathodes with carbon nanotubes (CNTs) and vapor grown carbon fiber (VGCF) were systematically studied to reveal that CNTs accelerate the electrochemical decomposition of sulfide electrolyte, despite the effectively improved electronic conductivity, rate capability and active material utilization. Therefore, in-situ coating of Li4C8H2O6 onto CNTs (Li4C8H2O6@CNT) is developed to further improve the contact between Li4C8H2O6 and CNTs, but to reduce the contact of CNTs with sulfide solid electrolyte and its decomposition. As a result, the Li4C8H2O6@CNT electrode demonstrates a high capacity of 200.3 mAh/g, and a high active material utilization rate (83.4% at 0.1C). It also exhibits a specific capacity of 85.9 mAh/g at a high cathode loading of 40 wt% and a high rate of 1C.

Construction of hierarchical Li3VO4/NC sponge structure for high-performance lithium storage

The practical application of Li3VO4 anodes for lithium-ion batteries has long been hindered by the intrinsically poor electronic conductivity and fabrication of stable electrodes. Herein, we design a hierarchical Li3VO4/NC sponge structure (H-LVO/NC SS) for achieving the adhesion of ultrasmall LVO nanoparticles on the N-doped carbon sponge. The structure effectively shortens the charge transport path, increases the effective contact between electrolyte and host material, and promotes reaction kinetics. Based on the structural advantages, the H-LVO/NC SS anode exhibits outstanding lithium storage performance in terms of high reversible specific capacity (710 mAh g−1 at 0.2 A g−1), excellent high-rate property (303 mAh g−1 at 8 A g−1 after 7 periodic rate performance) and superior cycling stability (266 mAh g−1 at the discharge current of 8 A g−1 after 4000 cycles). The pronouncedly improved electrochemical performance of H-LVO/NC SS demonstrates that this structure design strategy could provide a new reference for the new-generation electrode structures and provide in-depth insights for the structural design of other batteries.

Construction of the 12-Phosphomolybdate-based Coordination Polymer @ Crumpled Graphene Balls Composite as Anode for Lithium Batteries.

To address the poor electronic conductivity and conventionally lose easily of polyoxometalates (POMs), and considering the high electrical conductivity and configuration advantages of crumpled graphene balls (CGBs), herein, a series of POM-based coordination polymers [Cu(pyttz)2]PMo12@CGB (n, n = 1, 2, 3) were successfully synthesized, and electrochemical lithium storage performance and lithium ion diffusion kinetics were comprehensively investigated. Galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) study-confirm that [Cu(pyttz)2]PMo12@CGB (n, n = 1, 2, 3) integrates the advantage of high electronic conductivity of CGB and excellent Li+ migration kinetics of POMs, which greatly ameliorates the electrochemical performances of POMs, among [Cu(pyttz)2]PMo12@CGB (2) exhibits an excellent reversible specific capacity of around 941.4 mA h g-1 at 0.1 A g-1 after 150 cycles and admirable rate performance. This work will promote the development of POMCP anodes, thus fulfilling their potential in high-performance LIBs.

Tuning the electrochemical behaviors of N-doped LiMnxFe1–xPO4/C via cation engineering with metal-organic framework-templated strategy

LiFePO4, as a prevailing cathode material for lithium-ion batteries (LIBs), still encounters issues such as intrinsic poor electronic conductivity, inferior Li-ion diffusion kinetic, and two-phase transformation mechanism involving substantial structural rearrangements, resulting in unsatisfactory rate performance. Carbon coating, cation doping, and morphological control have been widely employed to reconcile these issues. Inspired by these, we propose a synthetic route with metal–organic frameworks (MOFs) as self-sacrificial templates to simultaneously realize shape modulation, Mn doping, and N-doped carbon coating for enhanced electrochemical performances. The as-synthesized LiMnxFe1–xPO4/C (x = 0, 0.25, and 0.5) deliver tunable electrochemical behaviors induced by the MOF templates, among which LiMn0.25Fe0.75PO4/C outperforms its counterparts in cyclability (164.7 mA h g−1 after 200 cycles at 0.5 C) and rate capability (116.3 mA h g−1 at 10 C). Meanwhile, the ex-situ XRD reveals a dominant single-phase solid solution mechanism of LiMn0.25Fe0.75PO4/C during delithiation, contrary to the pristine LiFePO4, without major structural reconstruction, which helps to explain the superior rate performance. Furthermore, the density functional theory (DFT) calculations verify the effects of Mn doping and embody the superiority of LiMn0.25Fe0.75PO4/C as a LIB cathode, which well supports the experimental observations. This work provides insightful guidance for the design of tunable MOF-derived mixed transition-metal systems for advanced LIBs.

Construction of highly conductive MoS2/MoO2/reduced graphene oxide nanocomposites for ultralong-life hybrid Mg2+/Li+ batteries

Hybrid Mg2+/Li+ batteries (MLIBs) are a promising battery system that combines the advantages of fast lithium-ion kinetics and dendrite-free magnesium deposition. Layered molybdenum disulfide (MoS2) has gained increasing interest due to larger layer spacing and weak van der Waals forces in MLIBs. However, poor intrinsic electronic conductivity hinders its practical application. Here, a highly conductive MoS2/MoO2/reduced graphene oxide (MoS2/MoO2/rGO) composite synthesized via a facile hydrothermal method is employed as a high-performance cathode material for MLIBs. The high electrical conductivity (7.5 ×10−3 S cm−1) and large specific surface area of MoS2/MoO2/rGO facilitate the rapid transport of interfacial electrons and provide abundant active sites for Mg2+/Li+ storage. The optimized MoS2/MoO2/rGO composite exhibits a high discharge capacity (297.3 mAh g−1) and excellent rate performance. Moreover, the composite electrode delivers ultra-long cycle life over 5000 cycles at 1000 mA g−1, with a capacity degradation rate of only 0.007 % per cycle. The results offer valuable insights for the development of highly conductive MoS2-based composites.

High-Performance Aqueous Zinc-Ion Batteries Based on Multidimensional V2O3 Nanosheets@Single-Walled Carbon Nanohorns@Reduced Graphene Oxide Composite and Optimized Electrolyte.

The drawbacks of poor electronic conductivity and structural instability during the cycling process limit the electrochemical property of vanadium-based cathode materials for aqueous zinc-ion batteries. In addition, continuous growth and accumulation of zinc dendrites can puncture the separator and cause an internal short circuit in the battery. In this work, a unique multidimensional nanocomposite is designed by a facile freeze-drying method with subsequent calcination, consisting of V2O3 nanosheets and single-walled carbon nanohorns (SWCNHs) crosslinked together and wrapped by reduced graphene oxide (rGO). The multidimensional structure can largely enhance the structural stability and electronic conductivity of the electrode material. Besides, additive Na2SO4 in the ZnSO4 aqueous electrolyte not only prevents the dissolution of cathode materials but also suppresses the Zn dendrite growth. After considering the influence of additive concentration on ionic conductivity and electrostatic force for electrolyte, V2O3@SWCNHs@rGO electrode delivers a high initial discharge capacity of 422 mAh g-1 at 0.2 A g-1 and a high discharge capacity of 283 mAh g-1 after 1000 cycles at 5 A g-1 in 2m ZnSO4 + 2m Na2SO4 electrolyte. Experimental techniques reveal that the electrochemical reaction mechanism can be expressed as the reversible phase transformation between V2O5 and V2O3 with Zn3(VO4)2.

Electrocatalytic Mechanism of Defect in Spinels for Water and Organics Oxidation.

Spinels display promising electrocatalytic ability for oxygen evolution reaction (OER) and organics oxidation reaction because of flexible structure, tunable component, and multifold valence. Unfortunately, limited exposure of active sites, poor electronic conductivity, and low intrinsic ability make the electrocatalytic performance of spinels unsatisfactory. Defect engineering is an effective method to enhance the intrinsic ability of electrocatalysts. Herein, the recent advances in defect spinels for OER and organics electrooxidation are reviewed. The defect types that exist in spinels are first introduced. Then the catalytic mechanism and dynamic evolution of defect spinels during the electrochemical process are summarized in detail. Finally, the challenges of defect spinel electrocatalysts are brought up. This review aims to deepen the understanding about the role and evolution of defects in spinel for electrochemical water/organics oxidation and provide a significant reference for the design of efficient defect spinel electrocatalysts.

Characteristics and electrochemical performances of nickel@nano‐silicon/carbon nanofibers composites as anode materials for lithium secondary batteries

AbstractSi is a next‐generation ideal anode material for Li‐ion batteries (LIBs) because of its high‐theoretical capacity (4200 mAh/g) and natural abundance. However, severe volume expansion and unstable solid electrolyte interface (SEI) film formation during lithiation/delithiation, and poor electron conductivity have significantly restricted the commercial application of Si. In this study, transition metal‐coated Si was synthesized and used as the anode material of LIBs. The transition metal salt of Ni was dissolved in an aqueous solution and used to coat the metal surface of Si nanoparticles. The coating was achieved by dropwise addition of metal solutions into Si dispersions. Thereafter, carbon nanofibers (CNFs) were grown on the transition metal‐coated Si nanoparticles via chemical vapor deposition method. The morphologies, compositions, and crystal quality of transition metal@Si/CNFs composites were characterized by transmission electron microscopy, scanning electron microscopy, x‐ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The electrochemical characteristics of the hybrid anodes were investigated using a coin cell and battery tester. Voltage profile measurements at 0.1 A/g of 0.02 M‐Ni@Si/CNFs composite showed satisfactory initial Coulombic efficiency of 85.6%; 0.01 M‐Ni@Si/CNFs composite exhibited high initial capacity of 1300.9 mAh/g retained to 828.4 mAh/g after 100 cycles, corresponding to 63.7% capacity retention. Even at high current densities, the 0.02 M‐Ni@Si/CNFs composite delivered 342.78 mAh/g of capacity at 5 A/g. This work realizes a Si‐based hybrid anode from Ni‐coated Si catalyst used for direct CNFs synthesis with a stable SEI layer, superior initial Coulombic efficiency with satisfactory cycle and rate performance suitable for commercialized advanced battery applications.

Facile Synthesizing Yolk-Shelled Fe3O4@Carbon Nanocavities with Balanced Physiochemical Synergism as Efficient Hosts for High-Performance Lithium–Sulfur Batteries

The severe “shuttle effect” of dissolved polysulfide intermediates and the poor electronic conductivity of sulfur cathodes cause capacity decay of lithium–sulfur batteries and impede their commercialization. Herein, we synthesized a series of well-designed yolk-shelled Fe3O4@carbon (YS-Fe3O4@C) nanocavities with different proportions of Fe3O4 as efficient sulfur hosts to stabilize polysulfide intermediates. The yolk-shelled nanocavity architectures were prepared through a facile method, which could effectively confine the active materials and achieve high conductivity. The polysulfide intermediate shuttle was successfully suppressed by a physiochemical synergism effect combining the retention of carbon shells and the adsorption of Fe3O4 nanoparticle cores. The highly conductive carbon shell provides efficient pathways for fast electron transportation. Meanwhile, the visible evolution of active materials and a reversible electrochemical reaction are revealed by in situ X-ray diffraction. With the balanced merits of enhanced electrical conductivity of carbon shell and optimal adsorption of Fe3O4 cores, the S/YS-27Fe3O4@C cathode (Fe3O4 accounts for 27 wt% in YS-Fe3O4@C) had the best electrochemical performance, exhibiting a high reversible specific capacity of 731.9 mAh g−1 and long cycle performance at 1 C (capacity fading rate of 0.03% over 200 cycles).