Utilization Of Active Material Research Articles

Research Progress on Multifunctional Modified Separator for Lithium–Sulfur Batteries

Lithium-sulfur batteries (LSBs) are recognized as one of the second-generation electrochemical energy storage systems with the most potential due to their high theoretical specific capacity of the sulfur cathode (1675 mAhg-1), abundant elemental sulfur energy storage, low price, and green friendliness. However, the shuttle effect of polysulfides results in the passivation of the lithium metal anode, resulting in a decrease in battery capacity, Coulombic efficiency, and cycle stability, which seriously restricts the commercialization of LSBs. Starting from the separator layer before the positive sulfur cathode and lithium metal anode, introducing a barrier layer for the shuttle of polysulfides is considered an extremely effective research strategy. These research strategies are effective in alleviating the shuttle of polysulfide ions, improving the utilization of active materials, enhancing the battery cycle stability, and prolonging the cycle life. This paper reviews the research progress of the separator functionalization in LSBs in recent years and the research trend of separator functionalization in the future is predicted.

Improving lithium polysulfides adsorption by oxygen-vacancy defects: By first-principles calculation

The serial interaction of lithium polysulfides (LiPSs) intermediates that possibly occurred on the surface of vacancy-defective manganese oxides have been investigated by First-principles calculation. Vacancy defects will cause the adjustment of micro regional electron density and produce stronger polarization for polar materials MnO2. The investigation of the stable adsorption site of LiPSs on defective MnO2 surface shows that oxygen-vacancy traps are beneficial for capturing LiPSs. Due to the existence of unpaired electrons, the interaction between vacancy-defective manganese oxide and Li2Sn molecules become stronger than pristine manganese oxide, which are propitious to decrease the adsorption energy for Li2Sn (n = 1, 2, 4, 6, 8) molecules. That is to say, vacancy defects can supply an effective nucleation sites that effectively enhance the affinity for Li2S and catalyze the conversion of LiPSs, which improve the shuttle effect and increase the utilization of active materials.

High-performance cathode promoted by reduced graphene oxide nanofibers with well-defined interconnected meso-/micro pores for rechargeable Li-Se batteries

Highly conductive nanostructures comprising one-dimensional (1D) reduced graphene oxide (rGO) nanofibers (NFs) and bimodal pores i.e., meso-/micropores, as efficient cathode hosts (Bi-P-rGO) for Li–Se batteries were prepared. The highly conductive rGO matrix acts as a self-supporting skeleton to enhance the structural integrity of the nanostructure besides providing numerous conducting pathways for rapid charge transfer. Moreover, highly interconnected chain-like mesopores guarantee efficient electrolyte percolation, whereas the micropores offer highly active material impregnation. Correspondingly, Bi-P-rGO@Se as a high-performance cathode was visualized, which demonstrated an overall enhanced electrochemical performance such as excellent rate capability (up to 20.0C) and overwhelming long-term cycling stability (73% capacity retention at the end of 800cycles with an average capacity decay rate of just 0.03% per cycle at 0.5C rate). The exceptional electrochemical performance of the Bi-P-rGO@Se cathode can be attributed to its highly porous structure, which promises efficient electrolyte infiltration and diffusion of charged species, high active material utilization within micropores, availability of conductive pathways for fast charge transfer, and high structural integrity. Therefore, we anticipate that the structural and electrochemical results presented in this work will provide significant insights into the synthesis of high-performance porous and conductive nanostructures for a wide range of applications.

Silicon Nanoparticles Embedded in Chemical-Expanded Graphite through Electrostatic Attraction for High-Performance Lithium-Ion Batteries.

Silicon (Si) is a promising next-generation anode for high-energy-density lithium-ion batteries. The application of silicon/carbon (Si/C) composites with high Si content is hindered by the huge volume change and insecure electrochemical interface of the Si anode. Herein, chemical-expanded graphite (CEG) is used as a carbon matrix to form Si@CEG/C composites with an embedded structure. CEG with an abundant pore structure and electropositivity can well disperse and accommodate a mass of Si nanoparticles (Si NPs). With the flexibility and porosity of CEG, the embedded structure of Si NPs fixed in an expanded graphite layer can adopt the volume change of Si NPs and offer the abundant path of diffusion of lithium-ion, which leads to a moderate cycle and rate performance. Si@CEG/C exhibits a high reversible capacity of 1232.4 mA h g-1 at a current density of 0.5 A g-1 and with a capacity retention rate of 87% after 200 cycles. This embedded structure of Si/C composites built by CEG is meaningful for the structure design of the Si-based anode with higher specific capacity, active material utilization, and satisfactory cycle stability.

Enabling stable cycling performance with rice husk silica positive additive in lead-acid battery

Lead-acid battery has been widely used in stationary energy storages, such as photovoltaic application, grid service and uninterrupted power system due to the advantages of high safety, recyclability, and low cost. However, the low cyclic performance limits its further applications in emerging functions. One of the main failure modes is caused by the high polarization on the PbO2 positive plate. Herein, the rice husk silica with hierarchical porous structure was used as the positive additive for preventing from the high polarization of the PbO2 positive plate. Nitrogen adsorption-desorption isothermal and X-ray diffraction confirmed that the hierarchical porous rice husk silica enlarged the electrochemical surface area of the PbO2 positive plate, endowing a high rate of active material utilization and low polarization during the charging process. Compared with the blank plate, the PbO2 plate with rice husk silica showed improved Coulombic efficiency and a prolonged cycle life. These notable features verify that the porous rice husk silica is a cost-effective positive additive for sustained lead-acid batteries.

A Review of Transition Metal Compounds as Functional Separators for Lithium‐Sulfur Batteries

AbstractLithium‐sulfur (Li−S) batteries have great potential for the development of next‐generation high‐energy‐density secondary batteries owing to their high theoretical energy density, active material (sulfur) environmental friendliness, and low cost. However, their application is still impeded by the inherent sluggish kinetics and solubility of intermediate products of the sulfur cathode. Interface design is an important direction to address challenges in the development of Li−S batteries. The modification of the separator has been shown to effectively suppress the shuttling effect of physical hindrance or chemical bonding without affecting the utilization of active materials. This review encompasses the application of nanostructured transition metal oxides (TMOs), transition metal sulfides (TMSs), transition metal nitrides (TMNs), transition metal phosphides (TMPs), such as incorporating functional separators beyond the approach for preparing novel cathodes, and discusses their composites in a new multifunctional barrier layer for Li−S batteries. The objective properties of various metal compounds and the effect of the shuttle effect in particular on the electrochemical performance in Li−S batteries are highlighted, and give an outlook on the promising approaches for the construction of reliable Li−S batteries.

Unveiling the anchoring and catalytic effect of Co@C3N3 monolayer as a high-performance selenium host material in lithium-selenium batteries: a first-principles study.

Suppressing the shuttle effect of high-order polyselenides is crucial for the development of high-performance host materials in lithium-selenium (Li-Se) batteries. Using first-principles calculations, the feasibility of Co@C3N3 monolayer as selenium cathode host material for Li-Se batteries is systematically evaluated from the aspects of binding energy, charge transfer mechanism, and catalytic effect of polyselenides in the present work. The Co@C3N3 monolayer can effectively prevent the solubilization of high-order polyselenides with large binding energy and charge transfer resulting from the synergistic effect of Li-N and Co-Se bonds. The polyselenides are inclined to adsorb on the surface of Co@C3N3 monolayer instead of interacting with the electrolytes, which effectively inhibits the shuttling of high-order polyselenides and improves cycling stability. The cobalt participation improves the conductivity of C3N3 monolayer, and the semi-metallic characteristics of the Co@C3N3 monolayer are maintained after the adsorption of Li2Sen (n = 1, 2, 4, 6, 8) or Se8 clusters, which is advantageous for the utilization of active selenium material. The crucial catalytic role of the Co@C3N3 monolayer is evaluated by examining the reduction pathway of Se8 and the decomposition barrier of Li2Se, and the results highlight the capability of Co@C3N3 monolayer to enhance the utilization of selenium and promote the transition of Li2Se. Our present work could not only provide valuable insights into the anchoring and catalytic effect of Co@C3N3 monolayer, but also shed light on the future investigation on the high performance C3N3-based host materials for Li-Se batteries.

Electrospun carbon-based nanomaterials for next-generation potassium batteries.

Rechargeable potassium (K) batteries that are of low cost, with high energy densities and long cycle lives have attracted tremendous interest in affordable and large-scale energy storage. However, the large size of the K-ion leads to sluggish reaction kinetics and causes a large volume variation during the ion insertion/extraction processes, thus hindering the utilization of active electrode materials, triggering a serious structural collapse, and deteriorating the cycling performance. Therefore, the exploration of suitable materials/hosts that can reversibly and sustainably accommodate K-ions and host K metals are urgently needed. Electrospun carbon-based materials have been extensively studied as electrode/host materials for rechargeable K batteries owing to their designable structures, tunable composition, hierarchical pores, high conductivity, large surface areas, and good flexibility. Here, we present the recent developments in electrospun CNF-based nanomaterials for various K batteries (e.g., K-ion batteries, K metal batteries, K-chalcogen batteries), including their fabrication methods, structural modulation, and electrochemical performance. This Feature Article is expected to offer guidelines for the rational design of novel electrospun electrodes for the next-generation K batteries.

A densely packed air-stable free-standing film with FeP nanoparticles@C@P-doped reduced graphene oxide for sodium-ion batteries.

Developing a facile strategy which enhances the structural stability and air/moisture stability of transition metal phosphides for practical applications is important but challenging. Herein, we designed a densely packed free-standing film consisting of carbon-coated FeP nanoparticles anchored on P-doped graphene (FeP@C@PG film) through solventless thermal decomposition and the roll-press method. Phytic acid serves a multifunctional role as both a phosphorus source to prepare ultrafine FeP nanoparticles and a protective layer to improve air stability along with hydrophobic graphene and maximize the utilization of phosphide. This structure can enhance electron/ion transport kinetics, allowing for full utilization of active materials, and buffer large volume expansions while preventing pulverization/aggregation during cycling. Noticeably, the densely packed structure can greatly enhance oxidation resistance by effectively blocking the penetration of air/moisture. Therefore, the FeP@C@PG film delivers a stable reversible capacity of 536.6 mA h g-1 after 1000 cycles at 1 A g-1 with good capacity retention, an excellent rate capability of 440.7 mA h g-1 at 5 A g-1, and excellent oxidation stability at 80 °C in air. Furthermore, a pouch-type full-cell exhibits excellent rate/cycling performance and bendability. This study provides a new direction for the rational design and practical applications of advanced P-based materials used in alkali metal-ion batteries.

Coupling of multiscale imaging analysis and computational modeling for understanding thick cathode degradation mechanisms

•PFIB allows the 3D imaging of large volumes relevant for statistical analyses •Information at both the nanoscale and microscale can be obtained in a timely manner •Particles cracking and contact loss in thick electrode result in degradation •The non-uniform CEI will accentuate the heterogeneities over long cycling Using a thick NMC811 (LiNi0.8Mn0.1Co0.1O2) electrode as an example, we present a macro- to nanoscale 2D and 3D imaging analysis approach coupled with 4D (space + time) computational modeling to probe its degradation mechanism in a lithium-ion battery cell. Particle cracking increases and contact loss between particles and carbon-binder domain are observed to correlate with the cell degradation. This study unravels that the reaction heterogeneity within the thick cathode caused by the unbalanced electron conduction is the main cause of the battery degradation over cycling. The increased heterogeneity in the system will entail more cathode regions where the degree of active material utilization is uneven, leading to higher probabilities of particle cracking. These findings shed light on the crucial role of the electronic and ionic transportation networks in the performance deterioration of the thick cathode. They also provide guidance for cathode architecture optimization and performance improvement. Using a thick NMC811 (LiNi0.8Mn0.1Co0.1O2) electrode as an example, we present a macro- to nanoscale 2D and 3D imaging analysis approach coupled with 4D (space + time) computational modeling to probe its degradation mechanism in a lithium-ion battery cell. Particle cracking increases and contact loss between particles and carbon-binder domain are observed to correlate with the cell degradation. This study unravels that the reaction heterogeneity within the thick cathode caused by the unbalanced electron conduction is the main cause of the battery degradation over cycling. The increased heterogeneity in the system will entail more cathode regions where the degree of active material utilization is uneven, leading to higher probabilities of particle cracking. These findings shed light on the crucial role of the electronic and ionic transportation networks in the performance deterioration of the thick cathode. They also provide guidance for cathode architecture optimization and performance improvement.

Advances and challenges in tuning the reversibility & cyclability of room temperature sodium–sulfur and potassium–sulfur batteries with catalytic materials

The high theoretical energy density of room temperature sodium-sulfur and potassium-sulfur batteries (Na–S; 1274 Wh/kg, K–S; 914 Wh/kg; based on the mass of sulfur) due to the multi-electron transfer associated with the unique conversion chemistry of S and the natural abundance of Na, K, and S raw materials make them ideal candidates for large-scale energy storage applications beyond Li batteries. However, achieving good reversibility, cyclability, and active material utilization in Na–S and K–S batteries demands alleviation of the complex polysulfide dissolution and the shuttle phenomena during cycling. Rational employment of catalytic materials is beneficial to address these issues by facilitating effective polysulfide transformation and thereby accelerating the sluggish reaction kinetics. This review focuses on the roles and evolution of catalytic materials in polysulfide adsorption, catalytic conversion, and redox mediation in facilitating high-performing Na–S and K–S batteries. Specifically, the advances in tuning the reversibility and cyclability of Na-S and K–S batteries strategically with catalytic material-incorporated S-host cathodes, separators, and interlayers and the interaction of various catalytic materials with the polysulfide species are discussed in the light of advanced characterization techniques. Lastly, the challenges and the plausible strategies for future research are elucidated.

Highly Efficient Organosulfur and Lithium‐Metal Hosts Enabled by C@Fe3N Sponge

AbstractLithium‐organosulfur (Li‐OS) batteries, despite possessing high theoretical specific capacity, encounter a few practical challenges, including unsatisfactory lifespan and low active material utilization under realistic conditions. Here, diisoropyl xanthogen polysulfide (DIXPS) has been selected as a model organosulfur compound to investigate the practical feasibility of Li‐OS batteries under realistic conditions. A well‐designed freestanding carbon sponge decorated with Fe3N nanoparticles (C@Fe3N) is introduced into the Li‐OS cells as a scaffold for both Li and DIXPS. The lithiophilic property of the C@Fe3N host guides uniform lithium deposition at the anode, and the catalysis of the DIXPS conversion reaction promotes the kinetics at the cathode. Impressively, the synergistic effect of C@Fe3N leads to an extremely stable cycling performance over 1 000 cycles in a Li‐OS full cell under realistic conditions.

Highly Efficient Organosulfur and Lithium-Metal Hosts Enabled by C@Fe3 N Sponge.

Lithium-organosulfur (Li-OS) batteries, despite possessing high theoretical specific capacity, encounter a few practical challenges, including unsatisfactory lifespan and low active material utilization under realistic conditions. Here, diisoropyl xanthogen polysulfide (DIXPS) has been selected as a model organosulfur compound to investigate the practical feasibility of Li-OS batteries under realistic conditions. A well-designed freestanding carbon sponge decorated with Fe3 N nanoparticles (C@Fe3 N) is introduced into the Li-OS cells as a scaffold for both Li and DIXPS. The lithiophilic property of the C@Fe3 N host guides uniform lithium deposition at the anode, and the catalysis of the DIXPS conversion reaction promotes the kinetics at the cathode. Impressively, the synergistic effect of C@Fe3 N leads to an extremely stable cycling performance over 1 000 cycles in a Li-OS full cell under realistic conditions.

Porous TiO2-x/C Nanofibers with Axially Aligned Tunnel Pores as Effective Sulfur Hosts for Stabilized Lithium-Sulfur Batteries.

Hierarchically porous TiO2-x/C nanofibers (NFs) with axially aligned cylindrical tunnel pore channels were synthesized as a sulfur (S) host for lithium-sulfur batteries (LSBs) by a microemulsion electrospinning method. We explored a synergistic chemical trapping reinforced by coordinatively unsaturated Ti3+ nuclei with oxygen deficiency (or more broadly via polar O-Ti-O units) in combination with physical trapping in both narrow pores (<5 nm) and larger ordered pore tunnels (20-100 nm) separated by thin walls to allow for a large volume of active material and rapid diffusion within the channels while effectively blocking out the diffusion of soluble lithium polysulfides. Due to this unique architecture and enhanced conductivity, the prepared materials enabled a high S loading (∼72 wt %) and significantly reduced the shuttle effect. Hence, the composite TiO2-x/C@S cathodes exhibited a high utilization of active materials, excellent rate performance, and promising cycling stability (retention of up to ∼1010 mAh g-1 after 150 cycles for the aerial capacity of 1.5 mAh cm-2, with very stable performance even for the high S loading of 2.5 mg cm-2). By designing control nanomaterials that lack either the pore tunnels or the desired chemical compositions, we elucidated the importance of the synergistic effect of both factors. This work demonstrates a successful exploration of oxide NFs with tunnel pores via a simple single-needle microemulsion electrospinning method, which should pave the way for similar nanomaterials engineering with other chemistries for improved LSB performance.

Revealing the accelerated reaction kinetic of Ni-rich cathodes by activated carbons for high performance lithium-ion batteries

Activated carbons (AC) play a key role in enabling the reaction kinetic of cathodes in lithium ion batteries (LIBs). However, the charge transfer dynamics and reaction kinetics mechanism of AC composited cathodes along their thickness direction are still poorly understood. Herein, we systematically compare the internal reactive process evolutions of AC modified LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes and pristine NCM622 cathodes at high C-rates. The charge transfer dynamic is revealed by the time of flight secondary ion mass spectrometry and X-ray photoelectron spectra analyzes. The addition of AC endows the NCM622 cathode regions close to the current collector possess higher lithium ion concentrations, meanwhile more Ni2+ can be converted into Ni3+. The results of COMSOL Multiphysics simulations based on the porous electrode theory is analyzed to explore reaction kinetics mechanism. AC in NCM622 cathodes homogenizes the reaction distributions, contributing to the boosted reaction kinetic, eventually, resulting in the high utilization of active materials. These findings provide a direct way to reduce solid-state diffusion resistances and accelerate reaction kinetics of electrodes, which is critical for developing batteries with long cycle stability and rate performance at high rates.

A Nickel-decorated porous graphitized carbon/sulfur cathode enabling excellent cycling stability of all-solid-state lithium-sulfur batteries

• A high electrical conductivity of Nickel-decorated porous graphitized carbon (Ni-PGC) host materials are prepared by a simple and effective calcination. • Ni-PGC-sulfur cathode realizes the fast redox kinetics of all-solid-state lithium-sulfur batteries. • Applying Ni-PGC-S material to all-solid-state Li-S battery can significantly improve the utilization of active materials. All-solid-state lithium-sulfur batteries (ASSLSBs) with high theoretical specific capacity and low cost are considered a promising electrochemical energy storage system. However, it suffers from large polarization, low sulfur utilization, and severe capacity decay, owing to the sluggish solid-solid reactions between sulfur and its discharging products (such as lithium sulfide, etc.). Herein, a Nickel-decorated porous graphitized carbon (Ni-PGC) is prepared using a one-step calcination method for the sulfur host in ASSLSBs with PEO-based solid electrolytes. The high specific surface area (638.2 m 2 g -1 ) of porous carbon structure with sufficient pore volume (0.69 cm 3 g -1 ) could uniformly disperse the active material (Sulfur). The metallic Nickel nanoparticles embedding in the porous network could significantly improve the electronic conductivity of composite cathode in ASSLSBs. As a result, the higher electrical conductivity of 8.22 S cm -1 is achieved from the Ni-PGC-S cathode, compared to 0.33 S cm -1 for the amorphous carbon-sulfur cathode. Furthermore, Li + diffusion coefficients (4.19×10 -11 cm 2 s -1 at the cathodic peak of 2.40 V, 7.54×10 -11 cm 2 s -1 at the cathodic peak of 2.05 V, and 2.69×10 -10 cm 2 s -1 at the anodic peak of 2.35 V) of the Ni-PGC-S cathode at 60 o C, are 11.11 times, 3.17 times and 2.17 times of the amorphous carbon-sulfur cathode without Ni doping. Therefore, the all-solid-state lithium-sulfur batteries assembled with the Ni-PGC-S cathode exhibit an extraordinary initial discharge capacity of 1311.3 mAh g -1 and a low cycling degradation (0.30 % per cycle) at 60 o C and 0.1 C. Even at 1 C, the battery delivers 375.8 mAh g -1 after 300 cycles.

From sparingly solvating to weakly solvating: Fine electrolyte regulation for lean-electrolyte Li-SeS2 batteries

The “solid-liquid-solid” reaction mechanisms of lithium-sulfur/selenium (Li-S/Se) batteries in ether-based electrolytes, which rely on the soluble polysulfides (Li2S4–8, LPSs)/polyselenides (Li2Se4–8, LPSes) intermediates, prevent further reduction of the electrolyte dosage and thus offset the advantages of Li-S/Se batteries in energy density. Using sparingly-solvating electrolytes, in which the dissolution of LPSs/LPSes is suppressed, could reduce the electrolyte dosage. Nevertheless, such electrolytes bring sluggish reaction kinetic and poor compatibility with lithium (Li) anodes. Herein, by regulating the electrolyte structure, we found the weakly-solvating electrolytes, which have slightly higher dissolubility of LPSs/LPSes than the sparingly-solvating ones, could facilitate electrochemical reaction and stabilize Li anodes. The newly formulated electrolyte makes high active materials utilization under conditions of high current densities, high areal mass loadings, and low electrolyte-to-active-material (E/A) ratio possible. The cell with a SeS2 cathode realizes a high discharge capacity of 1047 mAh g−1, 93.2% of its theoretical value (1123 mAh g−1), at 0.1 C. Even with a high areal-mass-loading SeS2 cathode (9.5 mg cm−2), the as-designed electrolyte endows the cell with a high reversible capacity of 713 mAh g−1 under a low E/A ratio of 1 μL mg−1. The as-proposed strategy provides an effective electrolyte-regulation solution to practical high-energy Li-S/Se batteries.

A novel three-dimensional ordered mesoporous microspheres comprising N-doped graphitic carbon-coated FexP nanoparticles as multifunctional interlayers to suppress polysulfide crossover in Li–S batteries

Highly porous and conductive microspheres comprising three-dimensionally ordered arrays of mesopores and biphasic iron phosphide (FexP) nanoparticles embedded into nitrogen-doped graphitic carbon (NGC) framework (P-FexP@NGC) were synthesized by spray pyrolysis method followed by phosphidation. The ordered arrays of mesopores (ϕ = 40 nm) were generated via the thermal breakdown of the polystyrene nanobeads (ϕ = 100 nm). The porous structure not only reduces the effective diffusion length for the charged species but also guarantees efficient electrode wetting along with the accommodation of undesired volume perturbations. The highly conductive NGC framework provides numerous conductive paths for rapid electron transfer, which facilitates kinetically favored redox reactions. Additionally, the polar biphasic FexP nanoparticles allow chemical confinement and catalytic conversion of trapped polysulfides, thus enhancing active material utilization. Correspondingly, the assembled Li–S cells featuring the P-FexP@NGC-coated separator exhibit good rate performance (350 mA h g−1 at 2.0C) and extended cycling stability at 0.1, 0.5, and 1.0C mainly due to high diffusion of charged species (diffusion coefficient (DLi+) = 10−7 cm2 s−1) and low charge transfer resistance. Even at high sulfur loading (3.46 mg cm−2) and a low electrolyte/sulfur ratio of 5.6 µL mg−1, the Li−S cells exhibit stable cycling performance.

In-situ evolution of CoS/C hollow nanocubes from metal-organic frameworks for sodium-ion hybrid capacitors

Alkaline ion hybrid capacitors bridge the performance gaps between batteries and supercapacitors by combining their merits in terms of energy and power densities. However, the poorly matched electrochemical kinetics between anodes and cathodes leads to reduced energy density and inadequate material utilization. Herein, a hybrid composite has been synthesized by the treatment of a cobalt-based metal–organic-framework (ZIF-67 nanocube), involving the chemical etching-coordination reaction and subsequent carbonization together with sulfidation treatment. The as-prepared material with a hollow structure is composed of nanosized CoS nanoparticles uniformly encapsulated in the mesoporous shells of carbon hollow nanocubes (CoS/C HC). The unique architecture endows CoS/C HC with abundant electrochemical active interfacial sites, good mechanical robustness, and effectively alleviated volume variation. CoS/C HC as electrode material exhibits distinguished sodium storage capabilities relating to specific capacity and prolonged cycling durability at high current densities. Moreover, a sodium-ion hybrid capacitor assembled by using CoS/C HC as anode and activated carbon as cathode delivers an energy density of 199 Wh kg−1 and a power density of 7113 W kg−1. The novel electrode material makes the hybrid capacitors more commercially possible by increasing the utilization of active material and improving structural stability.

High-Rate Organic Cathode Constructed by Iron-Hexaazatrinaphthalene Tricarboxylic Acid Coordination Polymer for Li-Ion Batteries.

The sluggish ion-transport in electrodes and low utilization of active materials are critical limitations of organic cathodes, which lead to the slow reaction dynamics and low specific capacity. In this study, the hierarchical tube is constructed by iron-hexaazatrinaphthalene tricarboxylic acid coordination polymer (Fe-HATNTA), using HATNTA as the self-engaged template to coordinate with Fe2+ ions. This Fe-HATNTA tube with hierarchical porous structure ensures the sufficient contact between electrolyte and active materials, shortens the diffusion distance, and provides more favorable transport pathways for ions. When employed as the cathode for rechargeable Li-ion batteries, Fe-HATNTA delivers a high specific capacity (244 mAh g-1 at 50 mA g-1 , 91% of theoretical capacity), excellent rate capability (128 mAh g-1 at 9 A g-1 ), and a long-term cycle life (73.9% retention over 3000 cycles at 5 A g-1 ). Moreover, the Li+ ions storage and conduction mechanisms are further disclosed by the ex situ and in situ characterizations, kinetic analyses, and theoretical calculations. This work is expected to boost further enthusiasm for developing the hierarchical structured metal-organic coordination polymers with superb ionic storage and transport as high-performance organic cathodes.