Electrodes For Energy Storage Research Articles

Solvent-freely polymerizing catechol and paraformaldehyde to nitrogen-rich carbon for high-volumetric-performance supercapacitor

Fabrication of nitrogen functionalized carbon with high nitrogen content (over 10 atom%) by a route with simplified and solvent-free procedures would be both economically and environmentally scalable. We demonstrate here a simple solvent-free route towards synthesizing porous carbon doped by nitrogen functionalties (21.7 atom%) involving solid state catalytic polymerization of catechol and paraformaldehyde with g-C3N4 as catalyst. Upon high-temperature treatment, the vaporized catechol and paraformaldehyde would be in situ polymerized on the surface of g-C3N4 forming the composite of g-C3N4@resin. During the following carbonization process, the resin was carbonized to carbon skeleton, while the g-C3N4 would be decomposed in situ doping the carbon skeleton. In our design, the avoidance of solvents in the whole synthesis procedure and the usage of g-C3N4 in the preparation not only reduces the waste production, but also introduces high nitrogen species (21.7 atom%). As electrode for supercapacitor, the resultant SFC based electrode achieves a large specific capacitance of 391F cm−3@1.0 A/g and high energy density of 34.5 Wh/L@1370 W/L, suggesting a potential as electrode for energy storage. And more, the developed method offers a promising and alternative route for the fabrication of new materials in manner of green and environmentally friendly.

Optimizing D-band center of tube brush-like CoZn13/Co/ZnO architecture with multiple-heterointerfaces enhancing ion/electron migration toward pseudocapacitive storage

The exploration of hierarchical heterostructures with heterointerfaces have proven indispensable for enhancing ion/electron migration of efficient energy storage. Herein, a fascinating design of CoZn13/Co/ZnO hierarchically porous nanostructures (CZCZ HPNs) with rich heterointerfaces concurrently encapsulated into N-doped carbon (NC), growing on three-dimensional Ni foam wrapped by N-doped graphene (denoted as CZCZ/NC HPNs) is showcased for pseudocapacitive storage. The ingeniously construction of CZCZ HPNs/NC features powerful built-in electric field (BIEF) introduced by well-defined heterointerface for boosting electronic/ionic transport dynamics, and unique porous hierarchical architectures for reinforcing the structural and electrochemical stability. Notably, combined with the differential charge density analysis, the BIEF in CZCZ/NC HPNs generated by two heterointerfaces of Co-ZnO and CoZn13-ZnO can offer additional driving forces for promoting electron transfer. The d band centers of different heterojunctions remarkably shift negatively in comparison with those of the monomers, indicative of lower electron/ion transfer energy barrier. Additionally, the CZCZ/NC HPNs as a positive electrode and porous γ-Fe2O3 nanorods wrapped by NC (γ-Fe2O3/NC) as a negative electrode are employed to assemble a soft-packed hybrid supercapacitor device with ultrahigh energy density of ∼107.2 Wh kg−1 at ∼399.9 W kg−1. This work highlights an in-depth fundamental understanding of underlying reaction mechanisms of the heterointerface and structures engineering in constructing other advanced electrodes in sustainable energy storage.

Co-precipitation synthesis of pseudocapacitive λ-MnO2 for 2D MXene (Ti3C2Tx) based asymmetric flexible supercapacitor

The rapid growth of wearable/portable electronics imposes a development of flexible, lightweight and highly efficient energy storage devices. In this work, we have synthesized λ-MnO2 nanoplates through one step co-precipitation method and used for flexible asymmetric supercapacitor (SC). The structural, morphological and electrochemical properties of synthesized λ-MnO2 were systematically investigated. The optical and electronic properties of λ-MnO2 were studied using UV–vis spectroscopy and density functional theory (DFT) calculations. The pseudocapacitive λ-MnO2 nanoplates-like electrode showed a maximum specific capacitance of 288.5 F g−1 at the scan rate of 5 mV s−1. To check the practicability, symmetric (λ-MnO2//λ-MnO2) as well as asymmetric (λ-MnO2//AC and λ-MnO2//Ti3C2Tx MXene) SCs were fabricated and their performances were compared. The asymmetric λ-MnO2//Ti3C2Tx MXene SC demonstrated a maximum energy density of 15.5 Wh kg−1 at the power density 1100 W kg−1 along with 86.3 % of capacitive retention after 5000 cycles. Besides, to confirm the suitability of these electrodes for flexible energy storage, a flexible λ-MnO2//Ti3C2Tx asymmetric SC was fabricated using PVA: Na2SO4 gel polymer electrolyte that operated in the potential window of 2 V and supplies high areal energy density of 39.9 μWh cm−2 at a power density of 8586 μW cm−2. Therefore, the λ-MnO2 prepared with a simple and scalable co-precipitation method may play a promising role in flexible energy storage.

A simple, validated approach for design of two-dimensional periodic particle patterns via acoustophoresis

Two-dimensional patterning of microparticles enables a wide range of functional materials, including patterned energy storage electrodes, flexible electronics, and sensor arrays. Particle patterning via acoustics offers an attractive path to generate a wide variety of 2D periodic patterns that introduce tailorable hierarchical porosity, useful for controlling surface area, transport distances, and other properties. This method is most effective with micron scale particles and patterns of tens to hundreds of microns. To enable systematic exploration of the broad design space for such patterns, this work develops a model of 2D and 3D assembly of particles at high loadings and validates the obtained patterns against both experiments and more computationally intensive modeling techniques. Using this simple model, connections are mapped between input parameters (like actuation conditions, particle volume fraction, material properties) and output geometrical features (like void size and shape, pattern connectivity, and surface area) so that they can be tailored to given applications. The utility of this simple model is illustrated by predicting and then experimentally demonstrating new hierarchical patterns resulting from multiple waves of different frequencies interacting. These multiscale patterns offer the potential to lift the limits on surface area, diffusion distances, and other features.

Electrochemical Performance of Corn Waste Derived Carbon Electrodes Based on the Intrinsic Biomass Properties.

The exploration of cost-effective and sustainable biomass-derived carbon materials as electrodes for energy conversion and storage has gained extensive attention in recent research studies. However, the selection of the biomass and the electrochemical performance regulation of the derived biochar, as well as their interrelationship still remain challenging for practical application. Herein, corn wastes with high carbon content (>40%), corn cob and corn silk, were selected as precursors for the preparation of high value-added and high yield carbon materials via a modified synthetic process. Uniquely, this work put emphasis on the theoretical and experimental investigations of how the biomass properties influence the composition and nanostructure regulation, the electrolyte ion adsorption free energy, and the electrical conductivity of the derived carbon materials as well as their electrochemical performance optimization. Owing to the favorable specific surface area, the hierarchical porous structure, and the diverse elemental distribution, corn cob and corn silk derived carbon materials (CBC and SBC) present great potential as promising electrodes for alkaline aqueous zinc batteries and supercapacitors. The assembled CBC//Zn and SBC//Zn zinc batteries deliver high energy densities of 63.0 Wh kg-1 and 39.1 Wh kg-1 at a power density of 575 W kg-1, with excellent cycling performance of 91.1% and 84.3% capacitance retention after 10,000 cycles. As for the assembled symmetric supercapacitors, high energy densities of 14.9 Wh kg-1 and 13.6 Wh kg-1, and superior long-term cycling stability of 99.3% and 96.6% capacitance retention after 20,000 cycles could be achieved. This study highlights the advantages of utilizing corn cob and corn silk as carbon sources on the designed synthesis of carbon electrodes, and presents a meaningful perspective in the investigation of biomass-derived carbon materials and their potential applications in rechargeable devices.

Sponge-like nanoporous activated carbon from corn husk as a sustainable and highly stable supercapacitor electrode for energy storage

Corn husk, an abundant agro-industrial waste was employed to produce activated carbon for energy storage. The sponge-like activated carbons were produced with environmentally friendly potassium carbonate (K2CO3) at different impregnation ratio (corn husk:K2CO3; 1:1 to 1:3) and activation temperatures (500–800 °C). The obtained activated carbon was used to produce electrodes for supercapacitor application. The results revealed that corn husk: K2CO3 ratio of 1:2 and 650 °C promoted mainly nanopores (0.773 nm) with appreciably higher specific surface area (1115 m2/g) and a sponge morphology. The electrochemistry performance test on the materials shows specific capacitances of up to 269 F/g at 5 mV/s scan rate for a material obtained at 650 °C. The textural characteristics, morphology, and heteroatoms of sulfur and nitrogen significantly promoted higher energy storage capacity. This activated carbon was employed to assemble a symmetric supercapacitor in acidic electrolyte (0.5 M H2SO4) that delivered up to ~10 Wh/kg and was very stable, maintaining about 99.5 % of its original energy after 20,000 charge/discharge cycles.

New Anderson-Based Polyoxometalate Covalent Organic Frameworks as Electrodes for Energy Storage Boosted Through Keto-Enol Tautomerization.

The unique electrochemical properties of polyoxometalates (POMs) render them ideal components for the fabrication of next-generation high-performance energy storage systems. However, their practical applications have been hindered by their high solubility in common electrolytes. This problem can be overcome by the effective hybridization of POMs with other materials. Here we present the design and synthesis of two novel polyoxometalate-covalent organic frameworks (POCOF) via one-pot solvothermal strategy between an amino-functionalized Anderson-type POM and a trialdehyde-based building unit. We show that structural and functional complexity can be enriched by adding hydroxyl groups in the 2,4,6 position to the benzene-1,3,5-tricarbaldehyde allowing to exploit for the first time in POCOFs the keto-enol tautomerization as additional feature to impart greater chemical stability to the COFs and enhanced properties leading to large specific surface area (347 m2 /g) and superior electrochemical performance of the POCOF-1 electrodes, when compared with POCOF-2 electrodes that possess only imine-type linkage and with pristine POM electrodes. Specifically, POCOF-1 electrodes display remarkable specific, areal, and volumetric capacitance (125 F/g, 248 mF/cm2 and 41.9 mF/cm3 , respectively) at a current density of 0.5 A/g, a maximum energy density (56.2 Wh/kg), a maximum power density (3.7 kW/kg) and an outstanding cyclability (90 % capacitance retention after 5000 cycles).

New Anderson‐Based Polyoxometalate Covalent Organic Frameworks as Electrodes for Energy Storage Boosted Through Keto‐Enol Tautomerization

AbstractThe unique electrochemical properties of polyoxometalates (POMs) render them ideal components for the fabrication of next‐generation high‐performance energy storage systems. However, their practical applications have been hindered by their high solubility in common electrolytes. This problem can be overcome by the effective hybridization of POMs with other materials. Here we present the design and synthesis of two novel polyoxometalate‐covalent organic frameworks (POCOF) via one‐pot solvothermal strategy between an amino‐functionalized Anderson‐type POM and a trialdehyde‐based building unit. We show that structural and functional complexity can be enriched by adding hydroxyl groups in the 2,4,6 position to the benzene‐1,3,5‐tricarbaldehyde allowing to exploit for the first time in POCOFs the keto‐enol tautomerization as additional feature to impart greater chemical stability to the COFs and enhanced properties leading to large specific surface area (347 m2/g) and superior electrochemical performance of the POCOF‐1 electrodes, when compared with POCOF‐2 electrodes that possess only imine‐type linkage and with pristine POM electrodes. Specifically, POCOF‐1 electrodes display remarkable specific, areal, and volumetric capacitance (125 F/g, 248 mF/cm2 and 41.9 mF/cm3, respectively) at a current density of 0.5 A/g, a maximum energy density (56.2 Wh/kg), a maximum power density (3.7 kW/kg) and an outstanding cyclability (90 % capacitance retention after 5000 cycles).

Sol-gel method preparation and high-rate energy storage of high-entropy ceramic (FeCoCrMnNi)C porous powder

Among the existing electrochemical capacitive energy storage electrode materials, the (TiNbTaZrHf)C, (VCrNbMoZr)2N, (CoCrFeMnNi)3O4, (FeCoCrMnMg)3O4 and (FeCoCrMnCuZn)3O4 all have excellent capacitive performance, but the energy density is limited due to the narrow potential window. In order to solve the problem of low energy density of electrochemical supercapacitor, a kind of high-entropy carbides (HEMCs) with broad potential window is designed from generalized analysis of electrochemical window of active elements. This high-entropy carbide contains five active elements of Fe, Co, Cr, Mn and Ni. The prepared HEMC-3 has abundant pores and a specific surface area of 417.8 m2 g−1. The large specific surface area makes the HEMCs have high-rate energy storage performance. Electrochemical tests show that the HEMC-3 presents a potential window of [-1.0, 0.6] versus Hg/HgO, and can obtain a specific capacitance of 169.7 F g−1 at a current density of 0.5 A g−1. Due to the designed wide potential window of the prepared HEMCs, the energy density has been greatly improved, which shows a new strategy for developing of electrochemical supercapacitor electrode materials.

Structurally-stable Mg-Co-Ni LDH grown on reduced graphene by ball-milling and ion-exchange for highly-stable asymmetric supercapacitor

As an electrode for energy storage, the inherently poor conductivity of metal hydroxides (MHs) can be improved by in situ growth of MHs on conductive carbon based substrates so that their performances on energy storage could be enhanced to a high level. However, the incompatibility of hydrophilic component (metal hydroxides) and hydrophobic counterpart (carbon based materials) makes it difficult to be accomplished. Herein, we presented a scalable and easy-operated strategy by ball-milling combined with ion-exchange technique to grow Mg-Co-Ni LDH (layered double hydroxides) on reduced graphene, in which ball-milling was utilized to disperse the staring material of magnesium acetate on graphene oxide (GO) to obtain the composite of Mg(Ac)2/GO. The composite can be in situ transformed to MgO/reduced grapheme (rG) by following heat treatment. While, the ion-exchange reaction could enables the in situ growth of Mg-Co-Ni LDHs on the reduced graphene. The derived products (denoted as Mg-Co-Ni LDH/rG-x) owns nanosheet morphology, surface area of 59–115 m2/g, homogenous elements distribution. As electrode for supercapacitor, the maximum capacitance of 1204F/g@1.0 A/g was achieved and the corresponding asymmetric supercapacitor device shows a large energy density of 44.3 Wh/kg@800 W/kg. Particularly, a superlong cycling stability with 90.5% capacitance retention of the first cycle was attained after continuous charge/discharge for 20 000 cycles at current density of 5.0 A/g, promising great potential for practical energy storage application. The present strategy is simple and scalable that can be widely applied to the synthesis of various hydroxides/oxides or multi-component hydroxides/oxides on carbon substrates forming a composite structure, thus offers a great potential for broad application areas including catalysis, adsorption, energy storage, etc.

High mass loading paper-based electrode material with cellulose fibers under coordination of zirconium oxyhydroxide nanoparticles and sulfosalicylic acid

With the rapid expansion of the flexible electronics market, it is critical to develop high-performance flexible energy storage electrode materials. Cellulose fibers, which are sustainable, low cost, and flexible, fully meet the requirements of flexible electrode materials, but they are electrically insulating and cause a decrease in energy density. In this study, high-performance paper-based flexible electrode materials (PANI:SSA/Zr-CFs) were prepared with cellulose fibers and polyaniline. A high mass loading of polyaniline was wrapped on zirconia hydroxide-modified cellulose fibers under metal-organic acid coordination through a facile in situ chemical polymerization process. The increase in mass loading of PANI on cellulose fibers not only improves the electrical conductivity but also enhances the area-specific capacitance of the flexible electrodes. The results of electrochemical tests show that the area specific capacitance of the PANI:SSA/Zr-CFs electrode is 4181 mF/cm2 at 1 mA/cm2, which is more than two times higher than that of the electrode with PANI on pristine CFs. This work provides a new strategy for the design and manufacture of high-performance flexible electronic electrodes based on cellulose fibers.

2D/2D nanoarchitecture of Ni/NiCo2O4 deposited onto reduced graphene oxide for high-performance hybrid supercapacitor applications

The advanced energy storage electrode materials should mainly be focused on nanoarchitecture, multiple redox states, large surface area, and plenty of surface-active sites. Thereby, designing well-defined nanostructured electrode materials and tailoring them with a suitable supporting material is a prime requirement for supercapacitor application. Herein, we report the facile solvothermal synthesis of Ni/NiCo2O4 nanosheets directly decorated onto reduced graphene oxide (rGO) followed by thermal treatment. The porous 2D/2D Ni/NiCo2O4@rGO framework could enable easier ion diffusion to the electroactive site with reduced resistance for charge and mass transportation. In addition, a 2D/2D nanoarchitecture with strong face-to-face contacts can provide an extremely coupling interface that exhibits to have tremendous potential for energy storage performance. Interestingly, the resulting Ni/NiCo2O4@rGO nanoarchitecture electrode exhibits a higher specific capacitance of 1110 F g−1 at a specific current of 1 A g−1, which is much higher than those of Ni/NiO@rGO (500 F g−1) and CoO/Co3O4@rGO (425 F g−1) electrodes under the similar condition. Besides, the Ni/NiCo2O4@rGO nanoarchitecture electrode shown considerably high specific capacitance (574 F g−1) even though the specific current increased to 20 A g−1, demonstrating that the nanoarchitecture electrode preserves good rate capability. Further, a hybrid supercapacitor was constructed using the Ni/NiCo2O4@rGO nanoarchitecture electrode, and it delivered a high specific capacitance of 127 F g−1, with a high energy density of 40.63 Wh kg−1 for a power density of 854.81 W kg−1. As well as the hybrid supercapacitor exhibited excellent long-term cyclability with 90.1 % retention over 20,000 charge-discharge cycles.

All-solid-state synthesis of nitrogen doped carbon with high-faradaic-active species for supercapacitor

Template synthesis of porous carbon with rich functionalities by a scalable strategy without using any solvents and activators will be a green and promising route. Herein, we reported an all-solid-state synthesis strategy by mixing glucose and graphitic carbon nitride (g-C3N4) by milling and then undergoing a segmented carbonization in which first at low temperature of 573 K to polymerize sucrose onto g-C3N4, then at high temperature of 973 K to carbonized the composite to obtain a porous carbon (denoted as GNC) with abundant nitrogen species over 20 atom% and large packing density (0.91–1.25 g cm−3). Due to the features of large packing density and rich electrochemically-active N species, as electrode for supercapacitive energy storage, the developed GNC exhibit a comparable energy storage level with both high gravimetric energy density of 26.8 Wh kg−1@1000 W kg−1 and volumetric energy density of 30.8 Wh L−1@1150 W L−1, suggesting a potentiality in energy storage field. Importantly, the present strategy owns characteristics of ease of operation, green and scalable, which would be a promising synthesis route towards the fabrication of functional carbon utilizing in many fields like sorption & separation, catalysis, energy storage and so on.

Construction of 3D interconnected NiCo2S4/bio-carbon coated Ni foam as binder-free electrode for high-performance supercapacitor

Although transition metal hydroxides/sulfides are considered as promising potential electrode materials for supercapacitors due to their excellent electrochemical activity, the low electrical conductivity, easy agglomeration of nanomaterials and poor rate performance seriously hinder their practical applications. Herein, we construct 3D interconnected binder-free electrode NiCo2S4/bio-carbon coated nickel foam (NiCo2S4/GRCNF) by growing NiCo2S4 nanosheets on the surface of low-cost and highly conductive GRCNF substrate via a simple hydrothermal reaction followed with subsequent sulfidation. As suggested by systematic characterizations, the advantages of obtained NiCo2S4/GRCNF include that the ultrathin 3D interconnected network of NiCo2S4 can furnish massive electrochemically active sites for faradic reaction, and the highly conductive GRCNF substrate promotes electron transfer and meanwhile prevents the aggregation of NiCo2S4 nanosheets. With a high specific capacitance of 7.71 F cm−2 at 3 mA cm−2, NiCo2S4/GRCNF has a huge application advantage over the contrast samples Ni-Co LDH/NF (3.29 F cm−2) and Ni-Co LDH/GRCNF (5.97 F cm−2). In addition, NiCo2S4/GRCNF shows a much higher rate performance (82.1%) than Ni-Co LDH/NF (44.5%) and Ni-Co LDH/GRCNF (66.4%). Furthermore, hybrid supercapacitor NiCo2S4/GRCNF//GNPC which is assembled with NiCo2S4/GRCNF as the anode possesses an impressive energy density of 0.429 mWh cm−2 at a power density of 7.023 mW cm−2 and good cycling stability (82.3% over 5000 cycles). The outstanding electrochemical performance of NiCo2S4/GRCNF suggests that the reported strategy provides new inspiration for the design and preparation of new binder-free composite electrodes for electrochemical energy storage.

Recent progress in green synthesized transition metal-based oxides in lithium-ion batteries as energy storage devices

Transition metal-based oxide nanoparticles have been greatly employed in many areas relevant to mankind and can be synthesized through various routes such as chemical, physical, and green synthesis methods. Research on green synthesized transition metal-based oxide materials with structure at nanometer scale has gained considerable attention over decades due to the synergy effects between the metal ion and phyto-constituents in the green element source. Researchers have reported that nanoparticles produced through green synthesis have glaring advantages such as fewer toxic impurities, environmentally benign, low-cost thrifty, high-rate performance, better stability, ability to control the particle's shape and size, amongst others when compared to others synthesized via conventional approaches. Consequent upon that, serious attentions is currently being deployed in the green chemistry education as the better alternative to achieve a sustainable and transformative innovative synthesis technique. This review highlights a brief outlook of green synthesis using leaf extract as a reducing/oxidizing agent, electrochemical properties of transition metal-based oxide nanoparticles synthesized via green synthesis. By focusing on green synthesis method using leaf extract, the hope is that such transformative innovative technique will enhance the production of high-rate performance transition metal-based oxide electrode for LIB and other high energy storage devices applications. This will drastically reduce the use of synthetic chemicals that pollutes environment.

Enhancing redox kinetics by electron orbital modulation for high-performance aqueous energy storage

The energy density of supercapacitors can be improved through rapid surface reconstruction of electrode materials in an alkaline medium. Transition metal sulfides (TMSs), including Co9S8, are widely used as energy storage electrode materials owing to their excellent structural characteristics. However, systematic research dealing with the enhancement of Co9S8 reconstruction ability induced by Se doping has not well been investigated. Herein, an electron orbital modulation strategy was developed to promote the reconfiguration capability of Co9S8 by substitution of the Se element. The theoretical simulation and experimental characterization confirmed the successful introduction of the Se element, resulting in more polarized charge distribution in Co9S8 and better charge transfer ability. The improved adsorption capacity of OH− also enhanced the intensity of surface reactions, as well as effectively increased the refactoring rate. The optimized Co9S5.1Se2.9 exhibited a specific capacitance of 1788.1 F g−1 at 1 A g−1. The assembled flexible asymmetric supercapacitor delivered a maximum energy density of 54.9 Wh kg−1. Overall, the proposed strategy can effectively be used to construct high energy density electrode materials with optimized reconstruction of dynamic rates through effective modulation of electron orbitals.

Carbon Nanocluster-Mediated Nanoblending Assembly for Binder-Free Energy Storage Electrodes with High Capacities and Enhanced Charge Transfer Kinetics.

The effective spatial distribution and arrangement of electrochemically active and conductive components within metal oxide nanoparticle (MO NP)-based electrodes significantly impact their energy storage performance. Unfortunately, conventional electrode preparation processes have much difficulty addressing this issue. Herein, this work demonstrates that a unique nanoblending assembly based on favorable and direct interfacial interactions between high-energy MO NPs and interface-modified carbon nanoclusters (CNs) notably enhances the capacities and charge transfer kinetics of binder-free electrodes in lithium-ion batteries (LIBs). For this study, carboxylic acid (COOH)-functionalized carbon nanoclusters (CCNs) are consecutively assembled with bulky ligand-stabilized MO NPs through ligand-exchange-induced multidentate binding between the COOH groups of CCNs and the surface of NPs. This nanoblending assembly homogeneously distributes conductive CCNs within densely packed MO NP arrays without insulating organics (i.e., polymeric binders and/or ligands) and prevents the aggregation/segregation of electrode components, thus markedly reducing contact resistance between neighboring NPs. Furthermore, when these CCN-mediated MO NP electrodes are formed on highly porous fibril-type current collectors (FCCs) for LIB electrodes, they deliver outstanding areal performance, which can be further improved through simple multistacking. The findings provide a basis for better understanding the relationship between interfacial interaction/structures and charge transfer processes and for developing high-performance energy storage electrodes.

Facet Dependence and Vacancy-Controlled Reversibility of the Spinel-to-Rocksalt Phase Transformation at Co3O4 Surfaces

Transition-metal spinel oxides have attracted considerable interest as high-performance electrodes for electrochemical energy storage and conversion, where irreversible or reversible spinel–rocksalt (S–R) phase transformation at the oxide surface has been frequently observed, which sensitively controls their performance. Exploring key factors controlling the S–R transformation and its reversibility at the atomic scale is important for understanding the electrochemical performance of spinel oxides. Using Co3O4 nanoparticles as an example, which represent a promising electrocatalyst for the oxygen evolution reaction, we present in situ atomic-scale imaging of the S–R transformation by using aberration-corrected scanning transmission electron microscopy combined with the integrated differential phase contrast imaging technique to visualize oxygen anions and transition-metal cations simultaneously. We reveal that the S–R transformation is not only determined by the oxygen vacancy formation energy but also largely controlled by the surface polarity of the reconstructed rocksalt layer, leading to a faster S–R transformation at the (001) surface than the (111) surface. Moreover, cobalt and oxygen vacancies are directly identified at the spinel/rocksalt interface, leading to the formation of an intermediate defective rocksalt phase and a two-step S–R transformation process. The existence of the intermediate defective rocksalt phase or not decisively controls the reversibility of the two-step S–R transformation. The uncovered facet dependence and vacancy-controlled reversibility of the S–R transformation provide important insights into the shape-dependent reactivity and stability of spinel oxide electrodes for electrochemical energy applications.

Effect of Electrode/Electrolyte Coupling on Birnessite (δ-MnO2) Mechanical Response and Degradation.

Understanding the deformation of energy storage electrodes at a local scale and its correlation to electrochemical performance is crucial for designing effective electrode architectures. In this work, the effect of electrolyte cation and electrode morphology on birnessite (δ-MnO2) deformation during charge storage in aqueous electrolytes was investigated using a mechanical cyclic voltammetry approach via operando atomic force microscopy (AFM) and molecular dynamics (MD) simulation. In both K2SO4 and Li2SO4 electrolytes, the δ-MnO2 host electrode underwent expansion during cation intercalation, but with different potential dependencies. When intercalating Li+, the δ-MnO2 electrode presents a nonlinear correlation between electrode deformation and electrode height, which is morphologically dependent. These results suggest that the stronger cation-birnessite interaction is the reason for higher local stress heterogeneity when cycling in Li2SO4 electrolyte, which might be the origin of the pronounced electrode degradation in this electrolyte.

Interlayer expanded VS2 nanosheet for efficient sodium storage

An interlayer-expanded vanadium disulfide (VS2) electrode has been developed to enhance the performance of sodium ion batteries. The interlayer expansion of the (001) plane from the standard 5.7 Å to 9.5 Å improves capacity by 2–3 times at various current densities even over long cycles. This advancement is credited to the optimized kinetics of Na+ diffusion, as the intrinsic structure of VS2 with weak van der Waals interlayer interactions leads to minimal resistance along 2D ionic diffusion routes. Our findings highlight the significance of interlayer engineering in designing efficient energy storage electrodes.