High-Mass-Loading Electrodes for Advanced Secondary Batteries and Supercapacitors

Establishing Nanoscale Circuitry by Designing a Structure with Atomic Short-range Order for High-Rate Energy Storage

High-rate materials necessitate the rapid transportation of both electrons and ions, a requirement that becomes especially challenging at practical mass loadings (>10 mg cm2). To address this challenge, a material is designed with an architecture having atomic-scale short-range order. This design establishes internal nanoscale circuitry at the particle level, which facilitates rapid electronic and ionic transport within micrometer-sized niobium tungsten oxides. The architecture features alternating cerium-depleted and cerium-enriched regions. The continuous cerium-enriched regions with enhanced conductivity provide multilane highways for electron mobility by functioning as electron-conducting wires that significantly boost the overall conductivity. The cerium-depleted regions effectively mitigate electrostatic repulsion and promote rapid ion transport through ion-conducting channels. These structural characteristics provide a continuous network that supports both electrical migration and chemical diffusion to amplify the areal capacity and rate capability even at high mass loadings. These findings not only expand the fundamental understanding of the design of optimal host lattices for advanced energy storage systems but also of the practical application of microsized high-rate electrode materials.

Engineering intervention to disrupt the evolution of ZIF-67: Ultra-fast synthesis of arrayed Co(OH)2@ZIF-L in dozens of seconds for high-energy charge storage

Designing rational heterostructures of high-performance electroactive materials on conductive substrates with hierarchical structures is critical for advancing electrochemical energy storage technologies. In this study, a unique spatial structure is fabricated by vertically aligning two-dimensional (2D) structures of Co-ZIF-L on conductive nickel foam (NF) substrate through interruption of ZIF-67 formation. This is followed by an innovative electrochemical synthesis method that disrupts unstable surface coordination bonds in Co-ZIF-L, enabling the in-situ generation of Co(OH)2. The resulting Co(OH)2@ZIF-L/NF binder-free electrodes feature a hierarchical spatial structure and are synthesized in approximately 30 s. These electrodes showcase exceptional area capacity of 3.1 C cm-2 at 1 mA cm-2, attributed to their high specific surface area and layered architecture that promotes electrolyte penetration. Density Functional Theory (DFT) calculations reveal that the Co(OH)2@ZIF-L nanostructures have superior electrical conductivity compared to the individual components. Furthermore, a hybrid supercapacitor (HSC) based on Co(OH)2@ZIF-L/NF//AC exhibits an impressive energy density of 42 Wh kg-1 at a power density of 184.7 W kg-1. This research provides new insights into the efficient synthesis of high-performance electroactive materials with unique spatial structures and expands the potential applications of ZIF materials.

Improving Electrochemical Performance of Ultrahigh-Loading Cathodes via the Addition of Multi-Walled Carbon Nanotubes

Achieving high energy densities in lithium-ion batteries requires advancements in electrode materials and design. This study investigated the incorporation of multi-walled carbon nanotubes (MWCNTs) with high commercial viability as conductive additives into two types of high-nickel cathode materials, LiNi0.8Co0.1Mn0.1O2 and LiNi0.92Co0.07Mn0.01O2. To ensure a uniform distribution within the electrodes, MWCNTs were uniformly dispersed in the solvent using ultrasonication, the most effective and straightforward dispersion method. This enhancement improved both electronic and ionic conductivity, facilitating the formation of an efficient electron transfer network. Unlike the cells using only carbon black, the electrodes with MWCNTs exhibited lower internal resistances, facilitating higher lithium-ion diffusion. The cells with MWCNTs exhibited a capacity retention of 89.5% over their cycle life, and the cells with 2 wt% MWCNTs exhibited a superior rate capability at a high current density of 1 C. This study highlights that incorporating well-dispersed MWCNTs effectively enhances the electrochemical performance of ultrahigh-loading cathodes in lithium-ion batteries (LIBs), providing valuable insights into electrode design.

Nondestructive Analysis of Commercial Batteries

Electrochemical batteries play a crucial role for powering portable electronics, electric vehicles, large-scale electric grids, and future electric aircraft. However, key performance metrics such as energy density, charging speed, lifespan, and safety raise significant consumer concerns. Enhancing battery performance hinges on a deep understanding of their operational and degradation mechanisms, from material composition and electrode structure to large-scale pack integration, necessitating advanced characterization methods. These methods not only enable improved battery performance but also facilitate early detection of substandard or potentially hazardous batteries before they cause serious incidents. This review comprehensively examines the operational principles, applications, challenges, and prospects of cutting-edge characterization techniques for commercial batteries, with a specific focus on in situ and operando methodologies. Furthermore, it explores how these powerful tools have elucidated the operational and degradation mechanisms of commercial batteries. By bridging the gap between advanced characterization techniques and commercial battery technologies, this review aims to guide the design of more sophisticated experiments and models for studying battery degradation and enhancement.

Carbon-Based 3D Architectures as Anodes for Lithium-Ion Battery Systems

Graphite, with its exceptional cyclic performance, continues to dominate as the preferred anode material for lithium-ion batteries. However as high-energy application gains momentum, there is growing demand for higher capacities that alloying/de alloying and conversion type anode materials can offer. Despite their potential, these materials are plagued by challenges such as volumetric fluctuations, low conductivities, and poor cyclic stability. Carbon nanostructures, on the other hand, show tremendous promise with their low volume expansion, high ion diffusion rates, and excellent conductivity. Nevertheless, their limited areal and volumetric densities restrict their widespread utilization. To address these limitations, various strategies such as doping, composite formation, and structural modification have been proposed. This article provides a succinct overview of carbon nanomaterials and their electrochemical performance as 3D carbon-based anodes, along with a comprehensive analysis of the strategies employed to overcome associated challenges while evaluating their potential prospects in the field.

Enhanced Electrochemical Performance of Carbon-Composited Co3O4 Microspheres as Anode Materials for Lithium-Ion Batteries

Cobalt (II, III) oxide (Co3O4) has recently gained attention as an alternative anode material to commercial graphite in lithium-ion batteries (LIBs) due to its superior safety and large theoretical capacity of about 890 mAh g-1. However, its practical application is limited by poor electrical conductivity and rapid capacity degradation because of significant volume increases and structural strain during repeated lithiation/delithiation cycles. To address these issues, this work presents a novel approach to synthesizing carbon-composited Co3O4 microspheres (Co3O4@C), using abietic acid (AA) as a carbon source to increase conductivity and structural stability. The resulting Co3O4@C anodes show an impressive discharge capacity of 1557.4 mAh g-1 after 200 cycling processes at a current density of 0.1 C, representing a significant improvement over bare Co3O4. This study demonstrates the potential of carbon-compositing as a strategy to mitigate the limitations of Co3O4 and extend its cyclability, making it a viable candidate for next-generation LIB anodes.

Promoted Stability and Reaction Kinetics in Ni-Rich Cathodes via Mechanical Fusing Multifunctional LiZr2(PO4)3 Nanocrystals for High Mass Loading All-Solid-State Lithium Batteries

Sulfide all-solid-state lithium battery (ASSLB) with nickel-rich layered oxide as the cathode is promising for next-generation energy storage system. However, the Li+ transport dynamic and stability in ASSLB are hindered by the structural mismatches and the instabilities especially at the oxide cathode/sulfide solid electrolyte (SE) interface. In this work, we have demonstrated a simple and highly effective solid-state mechanofusion method (1500 rpm for 10 min) to combine lithium conductive NASICON-type LiZr2(PO4)3 nanocrystals (∼20 nm) uniformly and compactly onto the surface of the single crystallized LiNi0.8Co0.1Mn0.1O2, which can also attractively achieve Zr4+ doping in NCM811 and oxygen vacancies in the LZPO coating without solvent and annealing. Benefiting from the alleviated interface mismatches, sufficient Li+ ion flux through the LZPO coating, promoted structural stabilities for both NCM811 and sulfide SE, strong electronic coupling effect between the LZPO and NCM811, and enlarged (003) d-spacing with enriched Li+ migration channels in NCM811, the obtained LZPO-NCM811 exhibits superior stability (185 mAh/g at 0.1C for 200 cycles) and rate performance (105 mAh/g at 1C for 1300 cycles) with high mass loading of 27 mgNCM/cm2 in sulfide ASSLB. Even with a pronounced 54 mgNCM/cm2, LZPO-NCM811 manifests a high areal capacity of 9.85 mAh/cm2. The convenient and highly effective interface engineering strategy paves the way to large-scale production of various coated cathode materials with synergistic effects for high performance ASSLBs.

Facile hydrothermal synthesis of a tri-metallic Cu-Mn-Ni oxide-based electrochemical pseudo capacitor

Transition metal oxide nanocomposites with heterostructures have gained a lot of attention for use in supercapacitors owing to their low cost, high surface area, fast transport of ions and electrons and high specific capacitance due to efficacious interplay between the electrode and the electrolytes. In this study, we fabricated tri-metallic Cu, Mn, Ni(CMNO), bi-metallic Mn, Ni(MNO) and mono-metallic Ni(NO) oxides through a facile hydrothermal route. All the fabricated materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDX), and their electrochemical properties were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). The CMNO material showed remarkable electrochemical performance with a specific capacitance of 790.63 F g-1 at a current density of 1 A g-1, surpassing the performance of MNO (438.4 F g-1) and NO (290.82 F g-1). Furthermore, CMNO showed high cycling stability with a retention of 96.7% specific capacitance after 8000 cycles. Based on remarkable and unique properties, the CMNO material is regarded as a promising material for new-generation pseudo-capacitor applications.

A robust polyaniline hydrogel electrode enables superior rate capability at ultrahigh mass loadings

Simultaneously achieving high mass loading and superior rate capability in electrodes is challenging due to their often mutually constrained nature, especially for pseudocapacitors for high-power density applications. Here, we report a robust porous polyaniline hydrogel (PPH) prepared using a facile ice-templated in situ polymerization approach. Owing to the conductive, robust, and porous nanostructures suitable for ultrafast electron and ion transport, the self-supporting pure polyaniline hydrogel electrode exhibits superior areal capacitance without sacrificing rate capability and gravimetric capacitance at an ultrahigh mass loading and notable current density. It achieves a high areal capacitance (15.2 F·cm-2 at 500 mA·cm-2) and excellent rate capability (~92.7% retention from 20 to 500 mA·cm-2) with an ultrahigh mass loading of 43.2 mg cm-2. Our polyaniline hydrogel highlights the potential of designing porous nanostructures to boost the performance of electrode materials and inspires the development of other ultrafast pseudocapacitive electrodes with ultrahigh loadings and fast charge/discharge capabilities.

Endogenous Interfacial Mo-C/N-Mo-S Bonding Regulates the Active Mo Sites for Maximized Li+ Storage Areal Capacity

Active sites, mass loading, and Li-ion diffusion coefficient are the benchmarks for boosting the areal capacity and storage capability of electrode materials for lithium-ion batteries. However, simultaneously modulating these criteria to achieve high areal capacity in LIBs remains challenging. Herein, MoS2 is considered as a suitable electroactive host material for reversible Li-ion storage and establish an endogenous multi-heterojunction strategy with interfacial Mo-C/N-Mo-S coordination bonding that enables the concurrent regulation of these benchmarks. This strategy involves architecting 3D integrated conductive nanostructured frameworks composed of Mo2C-MoN@MoS2 on carbon cloth (denoted as C/MMMS) and refining the sluggish kinetics in the MoS2-based anodes. Benefiting from the rich hetero-interface active sites, optimized Li adsorption energy, and low diffusion barrier, C/MMMS reaches a mass loading of 12.11 mg cm-2 and showcases high areal capacity and remarkable rate capability of 9.6 mAh cm-2@0.4 mA cm-2 and 2.7 mAh cm-2@6.0 mA cm-2, respectively, alongside excellent stability after 500 electrochemical cycles. Moreover, this work not only affirms the outstanding performance of the optimized C/MMMS as an anode material for supercapacitors, underscoring its bifunctionality but also offers valuable insight into developing endogenous transition metal compound electrodes with high mass loading for the next-generation high areal capacity energy storage devices.

Activating Ion Channels in Collapsed Hydrogel Derived Densified MXene Films with Cellulose Nanofibers to Overcome the Areal Versus Volumetric Capacitance Trade-Off

Concomitant achievement of all three performance pillars of a supercapacitor device, namely gravimetric, areal, and volumetric capacitance is a grand challenge. Nevertheless, its fulfilment is indispensable for commercial usage. Although, high compactness is the fundamental requirement to achieve high volumetric performance, it severely affects ion transportation in thick electrodes. Such trade-off makes it extremely challenging to realize very high areal and volumetric performance simultaneously. Here, a collapsed hydrogel strategy is introduced to develop MXene/cellulose nanofiber (CNF) based densified electrodes that offer excellent ion transportation despite a massive increase in areal mass loading (>70 mg cm-2). Quasi-oriented MXene/CNF (MXCF) hydrogels are produced through an electric field-guided co-assembly technique. Ambient dehydration of these hydrogels incorporates numerous pores in the resultant compact electrodes due to crumpling of the MXene sheets, while CNF ensures connectivity among the locally blocked pores in different length scales. The resultant collapsed MXCF densified electrode shows a remarkably high areal capacitance of 16 F cm-2 while simultaneously displaying a high volumetric capacitance of 849.8 F cm-3 at an ultrahigh mass loading of up to 73.4 mg cm-2. The universality of strategy, including the co-assembly of hydrogel and its collapse, is further demonstrated to develop high-performance asymmetric and wearable devices.

Immobile polyanionic backbone enables a 900-μm-thick electrode for compact energy storage with unprecedented areal capacitance

Thickening of electrodes is crucial for maximizing the proportion of active components and thus improving the energy density of practical energy storage cells. Nevertheless, trade-offs between electrode thickness and electrochemical performance persist because of the considerably increased ion transport resistance of thick electrodes. Herein, we propose accelerating ion transport through thick and dense electrodes by establishing an immobile polyanionic backbone within the electrode pores; and as a proof of concept, gel polyacrylic electrolytes as such a backbone are in situ synthesized for supercapacitors. During charge and discharge, protons rapidly hop among RCOO- sites for oriented transport, fundamentally reducing the effects of electrode tortuosity and polarization resulting from concentration gradients. Consequently, nearly constant ion transport resistance per unit thickness is achieved, even in the case of a 900-μm-thick dense electrode, leading to unprecedented areal capacitances of 14.85 F cm-2 at 1 mA cm-2 and 4.26 F cm-2 at 100 mA cm-2. This study provides an efficient method for accelerating ion transport through thick and dense electrodes, indicating a significant solution for achieving high energy density in energy storage devices, including but not limited to supercapacitors.

Enhancing Electrode Performance through Triple Distribution Modulation of Active Material, Conductive Agent, and Porosity

The increasing demand for large-scale energy storage propels the development of lithium-ion batteries with high energy and high power density. Low tortuosity electrodes with aligned straight channels have proved to be effective in building such batteries. However, manufacturing such low tortuosity electrodes in large scale remains extremely challenging. In contrast, high-performance electrodes with customized gradients of materials and porosity are possible to be made by industrial roll-to-roll coating process. Yet, the desired design of gradients combining materials and porosity is unclear for high-performance gradient electrodes. Here, triple gradient LiFePO4 electrodes (TGE) are fabricated featuring distribution modulation of active material, conductive agent, and porosity by combining suction filtration with the phase inversion method. The effects and mechanism of active material, conductive agent, and porosity distribution on electrode performance are analyzed by experiments. It is found that the electrode with a gradual increase of active material content from current collector to separator coupled with the distribution of conductive agent and porosity in the opposite direction, demonstrates the best rate capability, the fastest electrochemical reaction kinetics, and the highest utilization of active material. This work provides valuable insights into the design of gradient electrodes with high performance and high potential in application.

High-Area-Capacity Cathode by Ultralong Carbon Nanotubes for Secondary Binder-Assisted Dry Coating Technology

Thick electrodes with high mass loading and increased content of active materials are critical for achieving higher energy density in contemporary lithium-ion batteries (LIBs). Nonetheless, producing thick electrodes through the commonly used slurry coating technology remains a formidable challenge. In this study, we have addressed this challenge by developing a dry electrode technology by using ultralong multiwalled carbon nanotubes (MWCNT) as a conductive additive and secondary binder. The mixing process of electrode compositions and the fibrillation process of the polytetrafluoroethylene (PTFE) binder were optimized. The resulting LiCoO2 (LCO) electrode exhibited a remarkable mass loading of 48 mg cm-2 and an active material content of 95 wt %. Notably, the thick LCO electrode demonstrated a superior mechanical strength and electrochemical performance. After 100 cycles at a current density of 1/3 C, the electrode still exhibited a capacity retention of 91% of its initial capacity. This dry electrode technology provides a practicable and scalable approach to the powder-to-film LIB electrode manufacturing process.

Monolithic Microparticles Facilitated Flower-Like TiO2 Nanowires for High Areal Capacity Flexible Li-Ion Batteries

Flexible lithium-ion batteries (FLIBs) are intensively studied using free-standing transition metal oxides (TMOs)-based anode materials. However, achieving high areal capacity TMO-based anode materials is yet to be effectively elucidated owing to the poor adhesion of the active materials to the flexible substrate resulting in low active mass loading, and hence low areal capacity is realized. Herein, a novel monolithic rutile TiO2 microparticles on carbon cloth (ATO/CC) that facilitate the flower-like arrangement of TiO2 nanowires (denoted ATO/CC/OTO) is demonstrated as high areal capacity anode for FLIBs. The optimized ATO/CC/OTO anode exhibits high areal capacity (5.02 mAh cm-2@0.4 mA cm-2) excellent rate capability (1.17 mAh cm-2@5.0 mA cm-2) and remarkable cyclic stability (over 500 cycles). A series of morphological, kinetic, electrochemical, in situ Raman, and theoretical analyses reveal that the rational phase boundaries between the microparticles and nanowires contribute to promoting the Li storage activity. Furthermore, a 16.0 cm2 all-FLIB pouch cell assembled based on the ATO/CC/OTO anode and LiNiCoMnO2 cathode coated on ATO/CC (ATO/CC/LNCM) exhibits impressive flexibility under different folding conditions, creating opportunity for the development of high areal capacity anodes in future flexible energy storage devices.

Structural regulation of asphalt-based hard carbon microcrystals based on liquid-phase crosslinking to enhance sodium storage

Air-oxidation is an effective strategy to obtain promising carbon materials from asphalt for sodium-ion batteries. However, this method would generate a vast amount of gaseous pollutant, which pose challenges for recycling. Herein, a simple, cost-effective and environmentally friendly liquid-phase oxidation method is proposed. The oxygen-containing functional groups (-NO2) are introduced into asphalt, which effectively prevents the melting of asphalt and rearrangement of carbon layers during subsequent carbonization process. As a result, a carbon material with notable disorder degree, large interlayer spacing and abundant closed pores, is prepared. The as-prepared product demonstrates an impressive initial Coulombic efficiency of 88.3 % and an enhanced specific capacity of 317.0 mA h g-1, which is 2.6 times that of the pristine product. Moreover, when assembled with a Na3.32Fe2.34(P2O7)2 cathode, the full-cell delivers a high reversible capacity of 271.7 mA h g-1 at 30 mA g-1 with superb cycle life. This study offers a novel oxidation strategy and provides a solution for producing highly disordered carbon anodes from soft carbon precursors.

Organic Molecular Intercalation Enabled Anionic Redox Chemistry with Fast Kinetics for High Performance Magnesium Storage

Rechargeable magnesium-ion batteries possess desirable characteristics in large-scale energy storage applications. However, severe polarization, sluggish kinetics and structural instability caused by high charge density Mg2+ hinder the development of high-performance cathode materials. Herein, the anionic redox chemistry in VS4 is successfully activated by inducing cations reduction and introducing anionic vacancies via polyacrylonitrile (PAN) intercalation. Increased interlayer spacing and structural vacancies can promote the electrolyte ions migration and accelerate the reaction kinetics. Thanks to this "three birds with one stone" strategy, PAN intercalated VS4 exhibits an outstanding electrochemical performance: high discharge specific capacity of 187.2 mAh g-1 at 200 mA g-1 after stabilization and a long lifespan of 5000 cycles at 2 A g-1 are achieved, outperforming other reported VS4-based materials to date for magnesium storage under the APC electrolyte. Theoretical calculations confirm that the intercalated PAN can indeed induce cations reduction and generate anionic vacancies by promoting electron transfer, which can accelerate the electrochemical reaction kinetics and activate the anionic redox chemistry, thus improving the magnesium storage performance. This approach of organic molecular intercalation represents a promising guideline for electrode material design on the development of advanced multivalent-ion batteries.

Ultra-Dispersed α-MoC1-x Embedded in a Plum-Like N-Doped Carbon Framework as a Synergistic Adsorption-Electrocatalysis Interlayer for High-Performance Li-S Batteries

The shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) severely hinder the scalable application of lithium-sulfurr (Li-S) batteries. Herein, the highly dispersed α-phase molybdenum carbide nano-crystallites embedded in a porous nitrogen-doped carbon framework (α-MoC1-x @NCF) are developed via a simple metal-organic frameworks (MOFs) assisted strategy and proposed as the multifunctional separator interlayer for Li-S batteries. The inlaid MoC1-x nanocrystals and in situ doped nitrogen atoms provide a strong chemisorption and outstanding electrocatalytic conversion toward LiPSs, whereas the unique plum-like carbon framework with hierarchical porosity enables fast electron/Li+ transfer and can physically suppress LiPSs shuttling. Benefiting from the synergistic trapping-catalyzing effect of the MoC1-x @NCF interlayer toward LiPSs, the assembled Li-S battery achieves high discharge capacities (1588.1 mAh g-1 at 0.1 C), impressive rate capability (655.8 mAh g-1 at 4.0 C) and ultra-stable lifespan (a low capacity decay of 0.059% per cycle over 650 cycles at 1.0 C). Even at an elevated sulfur loading (6.0 mg cm-2 ) and lean electrolyte (E/S is ≈5.8 µL mg-1 ), the battery can still achieve a superb areal capacity of 5.2 mAh cm-2 . This work affords an effective design strategy for the construction of muti-functional interlayer in advanced Li-S batteries.

Insights into the Phase Purity and Storage Mechanism of Nonstoichiometric Na3.4 Fe2.4 (PO4 )1.4 P2 O7 Cathode for High-Mass-Loading and High-Power-Density Sodium-Ion Batteries

Mixed-anion-group Fe-based phosphate materials, such as Na4 Fe3 (PO4 )2 P2 O7 , have emerged as promising cathode materials for sodium-ion batteries (SIBs). However, the synthesis of pure-phase material has remained a challenge, and the phase evolution during sodium (de)intercalation is debating as well. Herein, a solid-solution strategy is proposed to partition Na4 Fe3 (PO4 )2 P2 O7 into 2NaFePO4  ⋅ Na2 FeP2 O7 from the angle of molecular composition. Via regulating the starting ratio of NaFePO4 and Na2 FeP2 O7 during the synthesis process, the nonstoichiometric pure-phase material could be successfully synthesized within a narrow NaFePO4 content between 1.6 and 1.2. Furthermore, the proposed synthesis strategy demonstrates strong applicability that helps to address the impurity issue of Na4 Co3 (PO4 )2 P2 O7 and nonstoichiometric Na3.4 Co2.4 (PO4 )1.4 P2 O7 are evidenced to be the pure phase. The model Na3.4 Fe2.4 (PO4 )1.4 P2 O7 cathode (the content of NaFePO4 equals 1.4) demonstrates exceptional sodium storage performances, including ultrahigh rate capability under 100 C and ultralong cycle life over 14000 cycles. Furthermore, combined measurements of ex situ nuclear magnetic resonance, in situ synchrotron radiation diffraction and X-ray absorption spectroscopy clearly reveal a two-phase transition during Na+ extraction/insertion, which provides a new insight into the ionic storage process for such kind of mixed-anion-group Fe-based phosphate materials and pave the way for the development of high-power sodium-ion batteries.

Etching-induced ion exchange engineering of two-dimensional layered NiFeCo-based hydroxides for high energy charge storage

Efficient and rapid synthesis of transition metal-based hydroxides with tailored microstructures has emerged as a promising approach to fabricate high-performance electrode materials for energy storage devices. However, many conventional synthesis methods are cumbersome, expensive and time-consuming, and the microstructures of electrode materials are usually uncontrollable. Herein, we propose a fast and cost-effective approach to electrochemically in situ grow NiFeCo-based ternary hydroxides (NiFeCo-THs) with layered nanosheet structures on pretreated nickel foam (NF). The in situ grown NiFeCo-THs were in direct contact with the NF to form a monolithic electrode as NiFeCo/NF. By engineering the ion exchange process for controlling the ionic ratio, the monolithic Ni1(Fe/Co = 1/1)0.5/NF electrode was fabricated and found to show the optimum electrochemical behavior with a specific capacitance of 2.32 C cm-2 at 2 mA cm-2 as a result of its characteristic microstructures. Furthermore, a hybrid supercapacitor was constructed utilizing the monolithic Ni1(Fe/Co = 1/1)0.5/NF electrode and activated carbon as the cathode and anode, respectively, and it was found to have an energy density of 81.1 μW h cm-2 at a power density of 808.8 μW cm-2. After 5000 cycles, 84.0% of the initial capacitance of the hybrid supercapacitor was maintained, and the monolithic Ni1(Fe/Co = 1/1)0.5/NF electrode still retained the arrayed nanosheet structure.

Atomic Layer Deposition-A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

Atomic layer deposition (ALD) has become the most widely used thin-film deposition technique in various fields due to its unique advantages, such as self-terminating growth, precise thickness control, and excellent deposition quality. In the energy storage domain, ALD has shown great potential for supercapacitors (SCs) by enabling the construction and surface engineering of novel electrode materials. This review aims to present a comprehensive outlook on the development, achievements, and design of advanced electrodes involving the application of ALD for realizing high-performance SCs to date, as organized in several sections of this paper. Specifically, this review focuses on understanding the influence of ALD parameters on the electrochemical performance and discusses the ALD of nanostructured electrochemically active electrode materials on various templates for SCs. It examines the influence of ALD parameters on electrochemical performance and highlights ALD's role in passivating electrodes and creating 3D nanoarchitectures. The relationship between synthesis procedures and SC properties is analyzed to guide future research in preparing materials for various applications. Finally, it is concluded by suggesting the directions and scope of future research and development to further leverage the unique advantages of ALD for fabricating new materials and harness the unexplored opportunities in the fabrication of advanced-generation SCs.

Coupling of Nd doping and oxygen-rich vacancy in CoMoO4@NiMoO4 nanoflowers toward advanced supercapacitors and photocatalytic degradation

In this paper, we successfully prepared rare earth element-doped 0.8% Nd-CoMoO4@NiMoO4 nanoflowers with a large specific surface area using the sol-gel method for the first time. In the experiment, we added a structure-directing agent to successfully assemble the nanosheets into a three-dimensional ordered micro-flower shape. By using the strategy of forming a flower-shaped morphology with a structure-directing agent and doping Nd elements to generate oxygen vacancies, the problems of the collapse of the active material structure and slow reaction kinetics were solved. Through relevant electrochemical performance tests, it was found that when the rare earth element Nd was doped at a concentration of 0.8%, the material exhibited exceptional specific capacitance (2387 F g-1 at 1 A g-1) and cycling stability (99.3% after 10 000 cycles at 5 A g-1). These performance characteristics far surpassed those of the other synthesized products. We assembled 0.8% Nd-CoMoO4@NiMoO4 with hydrophilic CNTs into an asymmetric device, 0.8% Nd-CoMoO4@NiMoO4//CNTs. This device exhibited high specific capacitance (262 F g-1 at 1 A g-1) and cycling stability (99.2% after 3000 cycles), with a good energy storage effect. In addition, 0.8% Nd-CoMoO4@NiMoO4 has a low band gap, which broadens the absorption range of the product and improves the utilization rate of visible light. The photocatalyst showed good degradation efficiency (all exceeding 96%) and cycling stability (96%) for all four dyes. This paper provides a new strategy and method for preparing doped polymetallic mixtures, which has potential application value.

Self-Discharge Processes in Symmetrical Supercapacitors with Activated Carbon Electrodes

The self-discharge of an electric double-layer capacitor with composite activated carbon electrodes and aqueous electrolyte (1 M MgSO4) was studied in detail. Under a long-term potentiostatic charge (stabilization), a decrease in the discharge capacity was observed in the region of voltages exceeding 0.8 V. The self-discharge process consists of two phases. In the initial phase, the cell voltage drop is due to the charge redistribution inside electrodes. During the main phase, the charge transfer between the electrodes determines the voltage drop. The optimal stabilization time of the self-discharge was found to be 50 min at 1.4 V. Hydrophilization of the negative electrode occurred during long-term polarization due to the formation of epoxy functional groups.

High Mass-Loading Biomass-Based Porous Carbon Electrodes for Supercapacitors: Review and Perspectives

Biomass-based porous carbon (BPC) with renewability and flexible nano/microstructure tunability has attracted increasing attention as efficient and cheap electrode materials for supercapacitors. To meet commercial needs, high mass-loading electrodes with high areal capacitance are preferred when designing supercapacitors. The increased mass percentage of active materials can effectively improve the energy density of supercapacitors. However, as the thickness of the electrode increases, it will face the following challenges including severely blocked ion transport channels, poor charging dynamics, poor electrode structural stability, and complex preparation processes. A bridge between theoretical research and practical applications of BPC electrodes for supercapacitors needs to be established. In this review, the advances of high mass-loading BPC electrodes for supercapacitors are summarized based on different biomass precursors. The key performance evaluation parameters of the high mass-loading electrodes are analyzed, and the performance influencing factors are systematically discussed, including specific surface area, pore structure, electrical conductivity, and surface functional groups. Subsequently, the promising optimization strategies for high mass-loading electrodes are summarized, including the structure regulation of electrode materials and the optimization of other supercapacitor components. Finally, the major challenges and opportunities of high mass-loading BPC electrodes in the future are discussed and outlined.

Fishnet-like double active layer-loaded carbon fiber for electrical double-layer capacitors

The rational design and controllable synthesis of high-performance energy storage materials are important measures to address the growing demand for energy storage devices. This work involves the growth of a fishnet-like Fe₂O₃ nanorod@oxygen-rich carbon layer structure directly onto carbon fiber cloth as a binder-free electrode for symmetric capacitors. The growth of Fe₂O₃ nanorods provided a large specific surface area, and the coating of an oxygen-rich carbon layer protected the Fe₂O₃ nanorods as an active substance. Furthermore, oxidation treatment created rich electrochemically active sites by loading oxygen-containing functional groups onto the composite surface. As a result, the optimal OC@Fe₂O₃-ACC sample exhibited a high areal specific capacitance of 1687 mF cm^-2 at a current density of 1 mA cm^-2. Meanwhile, an excellent capacity retention rate of 58.7% was achieved at 15 mA cm^-2. Finally, the long-term cycling stability was verified with an 80% retention rate of the initial capacitance after 12 000 cycles.

Nanostructured Thick Electrode Strategies toward Enhanced Electrode-Electrolyte Interfaces

This article addresses the issue of bulk electrode design and the factors limiting the performance of thick electrodes. Indeed, one of the challenges for achieving improved performance in electrochemical energy storage devices (batteries or supercapacitors) is the maximization of the ratio between active and non-active components while maintaining ionic and electronic conductivity of the assembly. In this study, we developed and compared supercapacitor thick electrodes using commercially available carbons and utilising conventional, easily scalable methods such as spray coating and freeze-casting. We also compared different binders and conductive carbons to develop thick electrodes and analysed factors that determine the performance of such thick electrodes, such as porosity and tortuosity. The spray-coated electrodes showed high areal capacitances of 1428 mF cm^-2 at 0.3 mm thickness and 2459 F cm^-2 at 0.6 mm thickness.

Tremella-like Vanadium Tetrasulfide as a High-Performance Cathode Material for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (RABs) are gaining widespread attention for large-scale energy storage applications as a result of their high energy densities, high security, and abundance. The key to sustain the progress of RABs lies in the quest for the proper cathode materials with prominent capacity and reversible cycle life. Herein, we propose a tremella-like VS₄ as a cathode material aiming to tackle this problem. Obtained from a morphology modification process, VS₄ with a unique nanosheet structure provides sufficient active sites for intercalation and conversion reactions, shortens the transport paths for charge carrier ions, and facilitates the infiltration process for electrolyte. The RAB with the VS₄ cathode exhibits excellent electrochemical performance, including outstanding specific capacity (407.9 mAh g^-1) and stable cycling performance (∼300 cycles at a high current density). The energy storage mechanism has been comprehensively investigated and is confirmed to be a combination of the intercalation/deintercalation of Al³⁺ and AlCl₄^- ions and conversion reaction by various techniques and DFT calculation. Our study not only provides a peculiar and simple strategy for the rational design of metal sulfide cathode materials with high capacity and long-term stability but also proposes a specific energy storage mechanism that guides the development of cathode materials of RABs in the future.

Interface Engineering of Zinc Electrode for Rechargeable Alkaline Zinc-Based Batteries

Rechargeable aqueous zinc-based batteries have gained considerable interest because of their advantages of high theoretical capacity, being eco-friendly, and cost effectiveness. In particular, zinc-based batteries with alkaline electrolyte show great promise due to their high working voltage. However, there remain great challenges for the commercialization of the rechargeable alkaline zinc-based batteries, which are mainly impeded by the limited reversibility of the zinc electrode. The critical problems refer to the dendrites growth, electrode passivation, shape change, and side reactions, affecting discharge capacity, columbic efficiency, and cycling stability of the battery. All the issues are highly associated with the interfacial properties, including both electrons and ions transport behavior at the electrode interface. Herein, this work concentrates on the fundamental electrochemistry of the challenges in the zinc electrode and the design strategies for developing high-performance zinc electrodes with regard to optimizing the interfaces between host and active materials as well as electrode and electrolyte. In addition, potential directions for the investigation of electrodes and electrolytes for high-performance zinc-based batteries are presented, aiming at promoting the development of rechargeable alkaline zinc-based batteries.

A zinc-conducting chalcogenide electrolyte

A solid-state zinc-ion battery can fundamentally eliminate dendrite formation and hydrogen evolution on the zinc anode from aqueous systems. However, enabling fast zinc ion ⁺ conduction in solid crystals is thought to be impossible. Here, we demonstrated a fluorine-doping approach to achieving fast Zn²⁺ transport in mesoporous Zn_yS_1-xF_x. The substitutional doping of fluoride ion with sulfide substantially reduces Zn²⁺ migration barrier in a crystalline phase, while mesopore channels with bounded dimethylformamide enable nondestructive Zn²⁺ conduction along inner pore surface. This mesoporous conductor features a high room-temperature Zn²⁺ conductivity (0.66 millisiemens per centimeter, compared with 0.01 to 1 millisiemens per centimeter for lithium solid-state electrolyte) with a superior cycling performance (89.5% capacity retention over 5000 cycles) in a solid zinc-ion battery and energy density (0.04 watt-hour per cubic centimeter) in a solid zinc-ion capacitor. The universality of this crystal engineering approach was also verified in other mesoporous zinc chalcogenide materials, which implies various types of potential Zn²⁺-conducting solid electrolytes.

Fabrication of Flexible All-Solid-State Asymmetric Supercapacitor Device via Full Recycling of Heated Tobacco Waste Assisted by PLA Gelation Template Method

In this study, a flexible all-solid-state asymmetric supercapacitor (FASC) device has been successfully fabricated via full recycling of heated tobacco waste (HTW). Tobacco leaves and cellulose acetate tubes have been successfully carbonized (HTW-C) and mixed with metal oxides (MnO2 and Fe3O4) to obtain highly active materials for supercapacitors. Moreover, poly(lactic acid) (PLA) filters have been successfully dissolved in an organic solvent and mixed with the as-prepared active materials using a simple paste mixing method. In addition, flexible MnO2- and Fe3O4-mixed HTW-C/PLA electrodes (C-MnO2/PLA and C-Fe3O4/PLA) have been successfully fabricated using the drop-casting method. The as-synthesized flexible C-MnO2/PLA and C-Fe3O4/PLA electrodes have exhibited excellent electrical conductivity of 378 and 660 μS cm-1, and high specific capacitance of 34.8 and 47.9 mF cm-2 at 1 mA cm-2, respectively. A practical FASC device (C-MnO2/PLA//C-Fe3O4/PLA) has been assembled by employing the C-MnO2/PLA as the positive electrode and C-Fe3O4/PLA as the negative electrode. The as-prepared FASC device showed a remarkable capacitance of 5.80 mF cm-2 at 1 mA cm-2. Additionally, the FASC device manifests stable electrochemical performance under harsh bending conditions, verifying the superb flexibility and sustainability of the device. To the best of our knowledge, this is the first study to report complete recycling of heated tobacco waste to prepare the practical FASC devices. With excellent electrochemical performance, the experiments described in this study successfully demonstrate the possibility of recycling new types of biomass in the future.

Hybrid Nano-Phase Ion/Electron Dual Pathways of Nickel/Cobalt-Boride Cathodes Boosting Intercalation Kinetics for Alkaline Batteries

Nickel-based hydroxides and their derivatives exhibit relatively low capacities and unsatisfactory durability as cathode materials for rechargeable alkaline batteries. In this work, a hybrid NiCo-B nanosheet cathode, integrating electrolyte ion-shuttling channels and electron-transferring networks into a metal-organic framework (MOF), was devised delicately. In the structure, the hybrid ion/electron dual pathways were constructed by NiCo-MOF frameworks and NiCo-B interpenetration networks. It revealed that nano-phase electron-transferring pathways in the MOF obviously boosted ion intercalation kinetics. The as-obtained hybrid NiCo-B nanosheets as cathode materials exhibited reversible capacity as high as 280 mA h g^-1 at a current density of 1 A g^-1 and excellent rate capability with a capacity retention of 78% from 1 to 10 A g^-1. After 2000 charge/discharge cycles at 4 A g^-1, the capacity still remained at 94% of the initial one. A full battery assembled with a hybrid NiCo-B cathode and a Fe₂O₃ anode showed a high capacity of 250 mA h g^-1 and a considerable stability of 89% after 1000 cycles. Ragone plots indicated the highest energy density of 409 W h kg^-1 and the lowest power density of 1.5 kW kg^-1, outperforming other aqueous batteries. It revealed that a syngenetic structure of ion/electron hybrid dual pathways integrated into an MOF could be a potential strategy to optimize ion intercalation electrode materials for alkaline batteries.

Enhanced Cyclability of LiNi0.6Co0.2Mn0.2O2 Cathodes by Integrating a Spinel Interphase in the Grain Boundary

Nickel-rich layered oxides are promising cathode materials for high-energy-density lithium-ion batteries. Unfortunately, the interfacial instability and intergranular cracks result in fast capacity fading and voltage fading during battery cycling. To address these issues, a coherent spinel interphase in the grain boundary of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) was successfully constructed via solution infusion and heat treatment. The results showed that the spinel (LiMn₂O₄) interphase could significantly reduce the formation of intergranular cracks during cycling. Meanwhile, the spinel structure on the primary particles effectively suppressed surface degradation, realizing the reduction of interface charge-transfer resistance and electrochemical polarization. As a result, the spinel-modified NCM cathode materials display superior electrochemical cyclability. The 1 wt % spinel phase-modified NCM delivers a discharge capacity of 154.1 mAh g^-1 after 300 cycles (1 C, 3-4.3 V) with an excellent capacity retention of 93%.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

In/Ce Co-doped Li3VO4 and Nitrogen-modified Carbon Nanofiber Composites as Advanced Anode Materials for Lithium-ion Batteries

Li₃VO₄ (LVO) is considered as a novel alternative anode material for lithium-ion batteries (LIBs) due to its high capacity and good safety. However, the inferior electronic conductivity impedes its further application. Here, nanofibers (nLICVO/NC) with In/Ce co-doped Li₃VO₄ strengthened by nitrogen-modified carbon are prepared. Density functional theory calculations demonstrate that In/Ce co-doping can substantially reduce the LVO band gap and achieve orders of magnitude increase (from 2.79 × 10^-4 to 1.38 × 10^-2 S cm^-1) in the electronic conductivity of LVO. Moreover, the carbon-based nanofibers incorporated with 5LICVO nanoparticles can not only buffer the structural strain but also form a good framework for electron transport. This 5LICVO/NC material delivers high reversible capacities of 386.3 and 277.9 mA h g^-1 at 0.1 and 5 A g^-1, respectively. Furthermore, high discharge capacities of 335 and 259.5 mA h g^-1 can be retained after 1200 and 4000 cycles at 0.5 and 1.6 A g^-1, respectively (with the corresponding capacity retention of 98.4 and 78.7%, respectively). When the 5LICVO/NC anode assembles with commercial LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) into a full cell, a high discharge capacity of 191.9 mA h g^-1 can be retained after 600 cycles at 1 A g^-1, implying an inspiring potential for practical application in high-efficiency LIBs.

Scalable 3D Honeycombed Co3O4 Modified Separators as Polysulfides Barriers for High-Performance Li-S Batteries

Lithium sulfur batteries (LSBs) are regarded as one of the most promising energy storage devices due to the high theoretical capacity and energy density. However, the shuttling lithium polysulfides (LiPSs) from the cathode and the growing lithium dendrites on the anode limit the practical application of LSBs. To overcome these challenges, a novel three-dimensional (3D) honeycombed architecture consisting of a local interconnected Co₃O₄ successfully assembled into a scalable modified layer through mutual support, which is coated on commercial separators for high-performance LSBs. On the basis of the 3D honeycombed architecture, the modified separators not only suppress effectively the "shuttle effects" but also allow for fast lithium-ions transportation. Moreover, the theoretical calculations results exhibit that the collaboration of the exposed (111) and (220) crystal planes of Co₃O₄ is able to effectively anchor LiPSs. As expected, LSBs with 3D honeycombed Co₃O₄ modified separators present a reversible specific capacity with 1007 mAh g^-1 over 100 cycles at 0.1 C. More importantly, a high reversible capacity of 808 mAh g^-1 over 300 cycles even at 1 C is also acquired with the modified separators. Therefore, this proposed strategy of 3D honeycombed architecture Co₃O₄ modified separators will give a new route to rationally devise durable and efficient LSBs.

Uniform Bi-Bi2O3 nanoparticles/reduced graphene oxide composites for high-performance aqueous alkaline batteries

Aqueous alkaline batteries (AABs) with the merits of both high energy density and power density have emerged as one of the most promising candidates for the new generation of energy storage devices, while their practical applications are still limited by the lack of high-performance electrode materials, especially for the anode materials. Herein, metallic bismuth-bismuth oxide nanoparticles (Bi-Bi₂O₃), with numerous heterogeneous interfaces, are successfully anchored and uniformly distributed on reduced graphene oxide (rGO) sheets. When Bi-Bi₂O₃/rGO-20 electrode is used as the anode material for an AAB, it shows a high specific capacity of 288.0 mA h g^-1 (1036.9 F g^-1) at 1 A g^-1 and good rate capability (74.7% of capacity retention ratio at 20 A g^-1). Additionally, in order to match well with a Bi-Bi₂O₃/rGO-20 anode, CoVS_x thin sheets decorated with Ni-Co layered double hydroxide sheets (NiCo-LDH) were successfully constructed via a facile multistep hydrothermal method and a subsequent electrodeposition process. The resulting cathode exhibits a high specific capacity of 306.0 mA h g^-1 (2448 F g^-1) at 1 A g^-1. The assembled CoVS_x@NiCo-LDH//Bi-Bi₂O₃/rGO-20 AAB delivers an outstanding energy density of 106.1 Wh kg^-1 at a power density of 789.6 W kg^-1. Besides, the as-synthesized Bi-based electrode is also used in aqueous Zn alkaline batteries to further extend its application and the assembled Bi-Bi₂O₃/rGO-20//Zn batteries possess an ultralong flat discharge plateau and exhibit a specific capacity of 250.6 mA h g^-1 at 1 A g^-1. The results demonstrate that the as-assembled AAB has huge potential for practical applications and provides an inspiration for the next-generation energy storage devices.

An Ultrafast, Durable, and High-Loading Polymer Anode for Aqueous Zinc-Ion Batteries and Supercapacitors

Zn metal has shown promise as an anode material for grid-level energy storage, yet is challenged by dendritic growth and low Coulombic efficiency. Herein, an ultrafast, stable, and high-loading polymer anode for aqueous Zn-ion batteries and capacitors (ZIBs and ZICs) is developed by engineering both the electrode and electrolyte. The anode polymer is rationally prepared to have a suitable electronic structure and a large π-conjugated structure, whereas the electrolyte is manufactured based on the superiority of triflate anions over sulfate anions, as analyzed and confirmed via experiments and simulations. This dual engineering results in an optimal polymer anode with a low discharge potential, near-theoretical capacity, ultrahigh-loading capability (≈50 mg cm^-2 ), ultrafast rate (100 A g^-1 ), and ultralong lifespan (one million cycles). Its mechanism involves reversible Zn²⁺ /proton co-storage at the carbonyl site. When the polymer anode is coupled with cathodes for both ZIB and ZIC applications, the devices demonstrate ultrahigh power densities and ultralong lifespans, far surpassing those of corresponding Zn-metal-based devices.

In Situ Anchoring Anion-Rich and Multi-Cavity NiS2 Nanoparticles on NCNTs for Advanced Magnesium-Ion Batteries

Magnesium (Mg)-ion batteries with low cost and good safety characteristics has attracted a great deal of attention recently. However, the high polarity and the slow diffusion of Mg²⁺ in the cathode material limit the development of practical Mg cathode materials. In this paper, an anion-rich electrode material, NiS₂ , and its composite with Ni-based carbon nanotubes (NiS₂ /NCNTs) are explored as the cathode materials for Mg-ion batteries. These NiS₂ /NCNTs with excellent Mg²⁺ storage property is synthesized by a simple in situ growth of NiS₂ nanoparticles on NCNTs. NiS₂ with both a large regular cavity structure and abundant sulfur-sulfur (SS) bonds with high electronegativity can provide a large number of active sites and unobstructed transport paths for the insertion-disinsertion of Mg²⁺ . With the aid of 3D NCNTs skeleton as the transport channel of the electron, the NiS₂ /NCNTs exhibit a high capacity of 244.5 mAh g^-1 at 50 mA g^-1 and an outstanding rate performance (94.7 mAh g^-1 at 1000 mA g^-1 ). It achieves capacitance retention of 58% after 2000 cycles at 200 mA g^-1 . Through theoretical density functional theory (DFT) calculations and a series of systematic ex situ characterizations, the magnesiation/demagnesiation mechanisms of NiS₂ and NiS₂ /NCNTs and are elucidated for fundamental understanding.

Mesoporous Ti4O7 nanosheets with high polar surface area for catalyzing separator to reduce the shuttle effect of soluble polysulfides in lithium-sulfur batteries

In the effort to accelerate adsorption and catalytic conversion of lithium polysulfides (Li-PSs) and suppress the shuttle effect of lithium-sulfur batteries (LSBs), the Ti 4 O 7 nanosheets/carbon material-modified separator is successfully fabricated to reducing soluble Li-PSs' crossover from cathode to anode. The catalyst of mesoporous Ti 4 O 7 nanosheets with O-Ti-O units synthesized at low temperature shows both excellent conductivity and high surface area. The modified separator can serve as a diffusion barrier of Li-PSs and catalyst for converting soluble low-chain sulfides into insoluble ones and then remarkably enhance the sulfur utilization and electrochemical performance of the LSB. This work provides a feasible avenue in both design and synthesis of mesoporous catalyst materials for suppressing the shuttle effect of lithium-sulfur batteries.

Water-in-salt electrolytes achieve high energy densities at an ultralow-temperature for aqueous symmetrical supercapacitors

LiTFSI/H₂O water-in-salt electrolytes with different concentrations show high energy densities for capacitive charge storage at sub-zero-temperatures (e.g. 32.23, 38.35 and 35 W h kg^-1 at 0, -10 and -20 °C, which are 1.44, 1.71 and 1.56 times that of normal temperature).

Interfacial charge storage mechanisms of composite electrodes based on poly(ortho-phenylenediamine)/carbon nanotubes via advanced electrogravimetry

To reach a deeper understanding of the charge storage mechanisms of electrode materials is one of the challenges toward improving their energy storage performance. Herein, we investigate the interfacial ion exchange of a composite electrode made of carbon nanotube/poly( ortho-phenylenediamine) (CNT/P oPD) in a 1M NaCl aqueous electrolyte via advanced electrogravimetric analyses based on electrochemical quartz crystal microbalance (EQCM). Classical EQCM at different scan rates of the potential revealed the complex electrogravimetric behavior likely due to multi-species participation at different temporal scales. Thereafter, in order to better understand the behavior of each species (ions, counter ions, and co-ions) in the charge compensation mechanism, the electrogravimetric impedance spectroscopy analysis (also called ac-electrogravimetry) was pursued. Ac-electrogravimetry revealed the role of each species where Na+ cations and Cl− anions as well as protons participate in the charge compensation mechanism of the CNT/P oPD composite with different kinetics and proportions. The water molecules with opposite flux direction with the cations are also detected, suggesting their exclusion during cationic species transfer. Having analyzed ac-electrogravimetry responses in depth, the synergistic interaction between the CNT and P oPD is highlighted, revealing the improved accessibility of species to new sites in the composite.

Highly dispersive CoSe2 nanoparticles encapsulated in carbon nanotube-grafted multichannel carbon fibers as advanced anodes for sodium-ion half/full batteries

Highly dispersive CoSe2 nanoparticles encapsulated in carbon nanotube-grafted multichannel carbon fibers are synthesized through a confined-regulated interfacial engineering strategy, which delivers excellent electrochemical performance.

Cobalt-based metal-organic framework electrodeposited on nickel foam as a binder-free electrode for high-performance supercapacitors

Cobalt-based metal-organic framework (Co-MOF) has been in-situ grown on nickel foam (NF) by cathodic electrodeposition using highly active cobalt surface modifier to enable uniform nucleation and tight growth of Co-MOF....