Reversible Specific Capacity Research Articles

Interconnected MoO2/MoS2@NC nanosheets as anodes with high-rate and long-life for lithium-ion and sodium-ion batteries

The development of sustainable and cost-effective anode materials with the ability to achieve superior performance in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) continues to pose a major challenge. Among the various available options, molybdenum-based materials have emerged as highly promising anodic candidates for both LIBs and SIBs owing to their substantial specific capacity, rapid electrochemical dynamics, and outstanding electronic conductivity. In this work, we present the preparation of molybdenum dioxide/molybdenum disulfide@nitrogen-doped carbon nanosheets (MoO2/MoS2@NC) via air-thermal activation. We highlight their exceptional lithium and sodium storage capabilities, which originate from their intricate hierarchical structures. As a result, the MoO2/MoS2@NC-15 composite has a remarkably high specific capacity (1027 mAh g−1 after 100 cycles at 100 mA g−1), high rate capability (490 mAh g−1 at 15000 mA g−1), and excellent cycling performance (618 mAh g−1 after 2000 cycles at 800 mA g−1) in LIBs. Moreover, in SIBs, the reversible specific capacity remaining is 246 mAh/g after 200 cycles at 600 mA g−1, which is indicative of a minimal capacity decrease of 0.4 mAh/g per cycle. Furthermore, comprehensive investigations were conducted on full cells comprising LIBs (MoO2/MoS2@NC-15//LiFePO4) and SIBs (MoO2/MoS2@NC-15//NaNi1/3Fe1/3Mn1/3O2), demonstrating their high specific capacities and excellent cycling performance. This study might provide a viable pathway toward developing straightforward and universally applicable synthesis methods for cutting-edge electrode materials in energy storage systems.

N-Containing Porous Carbon-Based MnO Composites as Anode with High Capacity and Stability for Lithium-Ion Batteries.

MnO has attracted much attention as the anode for Li-ion batteries (LIBs) owing to its high specific capacity. However, the low conductivity limited its large application. An effective solution to solve this problem is carbon coating. Biomass carbon materials have aroused much interest for being low-cost and rich in functional groups and hetero atoms. This work designs porous N-containing MnO composites based on the chemical-activated tremella using a self-templated method. The tremella, after activation, could offer more active sites for carbon to coordinate with the Mn ions. And the as-prepared composites could also inherit the special porous nanostructures of the tremella, which is beneficial for Li+ transfer. Moreover, the pyrrolic/pyridinic N from the tremella can further improve the conductivity and the electrolyte wettability of the composites. Finally, the composites show a high reversible specific capacity of 1000 mAh g-1 with 98% capacity retention after 200 cycles at 100 mA g-1. They also displayed excellent long-cycle performance with 99% capacity retention (relative to the capacity second cycle) after long 1000 cycles under high current density, which is higher than in most reported transition metal oxide anodes. Above all, this study put forward an efficient and convenient strategy based on the low-cost biomass to construct N-containing porous composite anodes with a fast Li+ diffusion rate, high electronic conductivity, and outstanding structure stability.

A three-dimensional Ge@C anode with a hollow and micro/nano structure for high-capacity lithium-ion battery

Aiming at the key issues of low intrinsic conductivity and large volume expansion during the cycling existed in high-capacity Ge anode material system, a micro/nano structured Ge@C hybrid material was designed and prepared through a facile and controllable method. The as-prepared micron conductive cage with a dodecahedral structure is composed of interconnected ultra-thin walled Ge nanotubes encapsulated in the porous N-containing carbon network, which can not only reserve more buffer space for the volume expansion of Ge and assist in building a stable SEI film during the cycling, improves the conductivity and stability of the material, but also provide a rich and penetrating channel for the transmission of ions, realizing high dynamics. When applied to the anode of lithium-ion battery, the three-dimensional micro/nano structured germanium-based hybrid material (Ge-3D@C) delivers a high initial specific capacity of 1500 mAh g−1 at 0.2 A g−1, and after 350 cycles, it can still maintain a high reversible specific capacity of 1147 mAh g−1. Even at high current densities of 1 A g−1 and 2 A g−1, high reversible specific capacities of 752 and 631 mAh g−1 can still be obtained. Importantly, the rational design can be used to prepare Ge hybrids doped with other metals or metal oxides, as well as different structures, by adjusting the layer materials and the types of germanates, so as to adapt to different application environments.

In-situ synthesis of yolk-shell Si/C anodes via ZnO transformation for high rate lithium-ion batteries

The conceptual design of yolk-shell structured Si/C composite materials is considered an effective approach to enhancing the structural stability of silicon-based anode materials over long cycles. Here, for the first time, zinc oxide is used as both the internal sacrificial layer and the external coating layer reactant, allowing it to be transformed into voids and the carbon layer precursor during subsequent operations. These internal voids can buffer the volume expansion of silicon, ensuring the electrode's integrity during cycling. The ZIF layer formed through in-situ solvothermal reactions can effectively reduce the occurrence of isolated ZIF in the solvent, resulting in better coating of the nano‑silicon particles. Compared to traditional processes for preparing yolk-shell structures, this gentle synthesis strategy avoids the use of HF, offering a new direction for large-scale production. This optimized yolk-shell Si/C-0.70 M electrode exhibits excellent rate performance (specific capacity of 988 mA h g−1 at a high current density of 2 A g−1) and long-term cycling stability (specific capacity of 722 mA h g−1 after 300 cycles at a current density of 0.5 A g−1; reversible specific capacity of 557 mA h g−1 after 500 cycles). Therefore, this scalable study offers a new approach for safely producing yolk-shell anode materials with high cycle stability on a large scale.

Binder-Free Intertwined Si and MnO2 Composite Electrode for High-Performance Li-Ion Battery Anode.

Silicon is considered as the most felicitous anode material candidate for lithium-ion batteries on account of abundant availability, suitable operating potential, and high specific capacity. Nevertheless, drastic volume expansion during the cycle impedes its practical utilization. Herein, Si and MnO2 (Si-MO) constructed the binder-free intertwined electrode that is reported to effectively improve upon the cycling stability of Si-based materials. The Si-based electrode without a binder has good electrical conductivity, strong adhesion to the substrate, and ample space for mitigating volume expansion. The incorporation of MnO2 establishes a multiphase interface, which mitigates the electrode volume expansion, and supports the electrode structure. Furthermore, MnO2 (∼1230 mAh g-1 theoretical capacity) synergistically enhances the overall capacity of the composite electrodes. Consequently, the Si-MO composite electrode exhibits a reversible specific capacity of 1300 mAh g-1 at 420 mA g-1 and remarkable cycling performance with a specific capacity of 830 mAh g-1 after 500 cycles. In particular, a reversible specific capacity of 837 mAh g-1 at 4200 mA g-1 is achieved and remains stable during 200 cycles. This work provides a potentially feasible way to achieve the Si-based anode commercialization for LIBs.

A soft carbon materials with engineered composition and microstructure for sodium battery anodes

Sodium-ion batteries (SIBs) have advantages in high sodium resources, providing powerful supplement to the current energy storage system. However, the lack of low-cost and high-performance anode materials still limits its practical application. Herein, a soft carbon anode derived from petroleum coke was successfully synthesized by engineering its composition and microstructure through resin and sodium phosphate compositing with optimal heat treatment process, delivering significant merits over existing composite anode in term of price density, initial Coulombic efficiency (ICE) and carbon yield. Resin helps to increase micropores and inhibit graphitization. Na3PO4 contributes to expand layer spacing and increase reversible groups, meanwhile facilitates the cross-linking of graphite microcrystalline and provides additional sodium supplement with improved ICE and conductivity. Through the synergistic effect by the additives, the optimized sample (P-ONH-1200) exhibits a superior reversible charge specific capacity of 311.9 mAh g−1 with high cycling stability, ICE (90.7 %) in SIBs, and high carbon yield (70 %). It also gains rate performance of 209.7 mAh g−1 at 4 C with 98 % retention after 1000 cycles. The full cell with Na3V2(PO4)3 (NVP) cathode at 1.05 N/P ratio exhibits an excellent stability with a capacity retention of 70 % after 500 cycles at 1 C. It provides a model reference for the microstructure regulation of petroleum coke and a revenue for preparation high-performance soft carbon anode for SIBs.

In Situ Phosphorization for Constructing Ni5P2-Ni Heterostructure Derived from Bimetallic MOF for Li-S Batteries.

Heterostructured materials commonly consist of bifunctions due to the different ingredients. For host material in the sulfur cathode of lithium-sulfur (Li-S) batteries, the chemical adsorption and catalytic activity for lithium polysulfides (LiPS) are important. This work obtains a Ni5P2-Ni nanoparticle (Ni5P2-NiNPs) heterostructure through a confined self-reduction method followed by an in situ phosphorization process using Al/Ni-MOF as precursors. The Ni5P2-Ni heterostructure not only has strong chemical adsorption, but also can effectively catalyze LiPS conversion. Furthermore, the synthetic route can keep Ni5P2-NiNPs inside of the nanocomposites, which have structural stability, high conductivity, and efficient adsorption/catalysis in LiPS conversion. These advantages make the assembled Li-S battery deliver a reversible specific capacity of 619.7 mAhg- 1 at 0.5C after 200 cycles. The in situ ultraviolet-visible technique proves the catalytic effect of Ni5P2-Ni heterostructure on LiPS conversion during the discharge process.

Constructing heterojunction-induced oxygen vacancies of N-doped carbon-encapsulated Sn/SnOx microplates for boosting lithium storage capability

Heterogeneous Sn/SnOx@N-doped carbon (Sn/SnOx@NC) microplates with oxygen vacancies evolved from plate-like SnO powders are successfully fabricated, in which SnO powders are converted into Sn, SnO2, and Sn2O3 phases by rationally sintering and are perfectly in situ encapsulated by polyaniline-derived NC layer. By elaborately constructing the particular structure, high discharge specific capacity of 730.4 mAh/g and capacity retention ratio of 98.3 % after 110 cycles at 0.1 A/g are realized for optimal Sn/SnOx@NC composite electrode. Benefiting from enhanced electronic conductivity and Li+ ions diffusion kinetics, the assembled cell delivers reversible discharge specific capacity of 487.3 mAh/g at 1.0 A/g after 500 cycles. First principles calculation and in/ex situ characterization reveal that in situ formed heterostructure with oxygen vacancies and NC layer synergistically improve interfacial charge transfer and reaction reversibility to promote lithium storage capability. Therefore, fabricating Sn/SnOx@NC microplates may provide a practical strategy to design heterogeneous and oxygen-deficient Sn-based anode materials for high-performance lithium-ion batteries.

Polyaniline layered N-doped carbon-coated iron oxide nanocapsules for extremely active Li-ion battery anode and oxygen evolution reaction

We report the effective synthesis of polyaniline (PANi)-layered nitrogen-doped carbon-coated Fe3O4 (FNC@PANi) nanocapsules (NCs) for electrocatalysis of oxygen evolution reaction (OER) as well as anode material for lithium (Li)-ion batteries (LIBs) via a simple hydrothermal method and oxidative polymerization technique. The prepared FNC@PANi NCs revealed a dual core-shell structure, in which an intermediate carbon layer allowed excellent electrical conduction between the Fe3O4 NCs and PANi. The dual core-shell structure also allowed the Fe3O4 NCs to expand freely during the Li-ion insertion/extraction and OER processes without breaking the outer layer, thus providing a high surface area (147.85 m2 g−1) and enhanced electrical conductivity. These properties facilitate the application of the dual core-shell FNC@PANi NCs as an advanced electrode material for LIBs, delivering a high reversible specific capacity of 1556.48 mAh g−1 at 0.1 A g−1, excellent rate performance (896.96 mAh g−1 at 1 A g−1), and durable cycling life (680.12 mAh g−1 at 5 A g−1 for 3000 cycles). The dual core-shell FNC@PANi NCs exhibited high electrocatalytic activity in the OER, with a small Tafel slope of 108.7 mV dec−1 owing to synergistic effects between the copious active sites of the Fe3O4 NCs and the carbon core-shell structure and a modest overpotential of 219 mV at 10 mA cm−2. The electrodes showed excellent stability over 10 h, as determined by chronopotentiometry at 10 mA cm−1. The resultant dual-core-shell FNC@PANi NCs are efficient iron-oxide-based electrode materials for LIBs and OER electrocatalysts.

Nitrogen-Doped Graphene-Like Carbon Intercalated MXene Heterostructure Electrodes for Enhanced Sodium- and Lithium-Ion Storage.

MXene is investigated as an electrode material for different energy storage systems due to layered structures and metal-like electrical conductivity. Experimental results show MXenes possess excellent cycling performance as anode materials, especially at large current densities. However, the reversible capacity is relatively low, which is a significant barrier to meeting the demands of industrial applications. This work synthesizes N-doped graphene-like carbon (NGC) intercalated Ti3C2Tx (NGC-Ti3C2Tx) van der Waals heterostructure by an in situ method. The as-prepared NGC-Ti3C2Tx van der Waals heterostructure is employed as sodium-ion and lithium-ion battery electrodes. For sodium-ion batteries, a reversible specific capacity of 305mAhg-1 is achieved at a specific current of 20mAg-1, 2.3 times higher than that of Ti3C2Tx. For lithium-ion batteries, a reversible capacity of 400mAhg-1 at a specific current of 20mAg-1 is 1.5 times higher than that of Ti3C2Tx. Both sodium-ion and lithium-ion batteries made from NGC-Ti3C2Tx shows high cycling stability. The theoretical calculations also verify the remarkable improvement in battery capacity within the NGC-Ti3C2O2 system, attributed to the additional adsorption of working ions at the edge states of NGC. This work offers an innovative way to synthesize a new van der Waals heterostructure and provides a new route to improve the electrochemical performance significantly.

Designing carboxymethyl cellulose based hydrogel electrolyte membranes enhanced by inorganic nanoparticle toward stable zinc anode

Aqueous zinc metal batteries have garnered substantial attention ascribing to affordability, intrinsic safety, and environmental benignity. Nevertheless, zinc metal batteries yet are challenged with potential service life issues resulted from dendrites and side reaction. In this paper, a strategy of nanoparticles doped hydrogel is proposed for constructing carboxymethyl cellulose/graphite oxide hybrid hydrogel electrolyte membranes with exceptional ionic conductivity, anti-swelling property, and simultaneously addressing the dendrites and parasitic reaction. The pivotal functions of the carboxymethyl cellulose/graphite oxide hydrogel electrolyte in mitigating hydrogen evolution and fostering accelerated Zn deposition have been elucidated based on principles of thermodynamic and reaction kinetic. The carboxymethyl cellulose/graphite oxide hydrogel electrolyte endows exceptional cycling longevity (800 h at 1 mA cm−2/1 mAh·cm−2) for Zn||Zn battery, as well as high Coulombic efficiency for Zn||Cu battery (averagely 99.14% within 439 cycles at 1 mA cm−2/1 mAh·cm−2). The assembled Zn||NH4V4O10 battery delivers a high reversible specific capacity of 328.5 mAh·g−1 at 0.1 A g−1. Moreover, the device of Zn||NH4V4O10 pouch battery remains operational under severe conditions like bending and cutting. This work provides valuable reference in developing inorganic nanoparticle hybrid hydrogel electrolyte for realizing high-performance zinc metal batteries.

Enhanced performance of Mo-doped TiNb2O7 anode material for lithium-ion batteries via KOH sub-molten salt synthesis

TiNb2O7 (TNO) as an electrode material for lithium-ion batteries (LIBs) has relatively high safety and high theoretical capacity, making it an excellent alternative to the graphite anode. Nevertheless, its practical application is limited by its sluggish ionic and electronic conductivity. To address this challenge, Mo-doped TiNb2O7 (Mo-TNO) is synthesized via a KOH sub-molten salt method followed by calcining process. In this method, the low-cost raw materials are co-dissolved and then coprecipitated to achieve homogeneous mixing and particle refinement, further ensuring the uniformity of calcined products. The doping of Mo6+ facilitates cation mixing and charge compensation, leading to reduced charge transfer resistance and enhanced electronic conductivity. The reversible specific capacity of Mo-TNO after 300 cycles is maintained at 148 mA h g−1 with a high capacity-retention of 80 % at 5C. Even at 30C, it still exhibits a better capacity of 100.2 mA h g−1, much higher than the pristine TNO (58.9 mA h g−1). Furthermore, the full battery employing Mo-TNO as an anode and commercial LiNi0.6Co0.2Mn0.2O2 (NCM) as a cathode exhibits superior electrochemical performances with promising application prospect. These findings underscore the significant potential of Mo-TNO as a high-rate and long-life anode material for LIBs.

Modification of LiMn0·6Fe0·4PO4 lithium-ion battery cathode materials with a fluorine-doped carbon coating

In this study, glucose and NH4F were utilized as sources of carbon and fluorine, respectively, for the synthesis of LiMn0·6Fe0·4PO4 (LMFP) nanoscales. These nanoscales were subsequently modified with varying levels of fluorine-doped carbon through co-precipitation and mechanical ball milling processes. The LMFP, incorporating carbon and varying levels of fluoride ions, exhibit higher specific discharge capacities at 0.2 Cand electrochemical characteristics compared to the original LMFP coated solely with carbon. The inclusion of fluorine-doped carbon in the composite material creates numerous pathways for expeditious electron transfer. Moreover, the partial formation of metal fluoride at the interface between the surface of LMFP and the layer of carbon coating doped with fluorine enhances the reduction in the charge-transfer resistance. The modified ferromanganese phosphate cathode material reveals an outstanding discharge capacity displaying a reversible discharge specific capacity value of 131.73 mA h g−1 at 10C and 154.6 mA h g−1 at 0.2C, due to its unique structure.

Localized High-Concentration Sulfone Electrolytes with High-Voltage Stability and Flame Retardancy for Ni-Rich Lithium Metal Batteries.

The localized high-concentration electrolyte (LHCE) propels the advanced high-voltage battery system. Sulfone-based LHCE is a transformative direction compatible with high energy density and high safety. In this work, the application of lithium bis(trifluoromethanesulphonyl)imide and lithium bis(fluorosulfonyl)imide (LiFSI) in the LHCE system constructed from sulfolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is investigated. The addition of diluent causes an increase of contact ion pairs and ionic aggregates in the solvation cluster and an acceptable quantity of free solvent molecules. A small amount of LiFSI as an additive can synergistically decompose with TTE on the cathode and participate in the construction of both electrode interfaces. The designed electrolyte helps the Ni-rich system to cycle firmly at a high voltage of 4.5V. Even with high mass load and lean electrolyte, it can keep a reversible specific capacity of 91.5% after 50 cycles. The constructed sulfone-based electrolyte system exhibits excellent thermal stability far beyond the commercial electrolytes. Further exploration of in-situ gelation has led to a quick conversion of the designed liquid electrolyte to the gel state, accompanied by preserved stability, which provides a direction for the synergistic development of LHCE with gel electrolytes.

Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications.

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g-1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al2O3 flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g-1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al2O3 layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al2O3 materials maintain a high capacity of 525 mAh g-1 at a current density of 50 mA g-1. Remarkably, at a higher current density of 2000 mA g-1, these materials still achieve a capacity of 220 mAh g-1. Moreover, after 200 cycles at a current density of 200 mA g-1, a high charge capacity of 319 mAh g-1 is sustained. In addition, a full cell consisting of a CuO@Al2O3 anode and a NaNi1/3Fe1/3Mn1/3O2 cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.

High capacity adsorption of antimony by hollow Co-MnO2 and its consequential utilization in SbO2--based aqueous batteries

Toxic metal pollution is one of the environmental problems that seriously affect water resources and ecosystems. Antimony, recognized for its teratogenic and carcinogenic properties, poses significant health risks due to its widespread presence in natural water sources. In this study, cobalt-doped manganese oxide bimetallic composites were designed as an efficient adsorbent for the antimony removal from water. The adsorbent exhibits robust performance over a range of pH values, achieves a significant adsorption capacity of 591.1 mg/g, and exhibits adsorption equilibrium within 25 min. The effectiveness of the adsorption is attributed to the interaction between metal-O bonds and antimony, as well as the hydrogen bonding. In line with the concept of sustainable development, waste adsorbents are used as negative electrodes for SbO2--based aqueous alkaline batteries. It exhibits a high reversible specific capacity of 122.8 mAh·g−1. This research not only sheds light on innovative approaches to antimony removal but also opens up avenues for the sustainable reuse of waste materials, in line with the principles of sustainable development.

Additive-Free Anode with High Stability: Nb2CTx MXene Prepared by HCl-LiF Hydrothermal Etching for Lithium-Ion Batteries.

MXenes, represented by Ti3C2Tx, have been widely studied in the electrochemical energy storage fields, including lithium-ion batteries, for their unique two-dimensional structure, tunable surface chemistry, and excellent electrical conductivity. Recently, Nb2CTx, as a new type of MXene, has attracted more and more attention due to its high theoretical specific capacity of 542 mAh g-1. However, the preparation of few-layer Nb2CTx nanosheets with high-quality remains a challenge, which limits their research and application. In this work, high-quality few-layer Nb2CTx nanosheets with a large lateral size and a high conductivity of up to 500 S cm-1 were prepared by a simple HCl-LiF hydrothermal etching method, which is 2 orders of magnitude higher than that of previously reported Nb2CTx. Furthermore, from its aqueous ink, the viscosity-tunable organic few-layer Nb2CTx ink was prepared by HCl-induced flocculation and N-methyl-2-pyrrolidone treatment. When using the organic few-layer Nb2CTx ink as an additive-free anode of lithium-ion batteries, it showed excellent cycling performance with a reversible specific capacity of 524.0 mAh g-1 after 500 cycles at 0.5 A g-1 and 444.0 mAh g-1 after 5000 cycles at 1 A g-1. For rate performance, a specific capacity of 159.8 mAh g-1 was obtained at a high current density of 5 A g-1, and an excellent capacity retention rate of about 95.65% was achieved when the current density returned to 0.5 A g-1. This work presents a simple and scalable process for the preparation of high-quality Nb2CTx and its aqueous/organic ink, which demonstrates important application potential as electrodes for electrochemical energy storage devices.

Hydrothermally Assisted Conversion of Switchgrass into Hard Carbon as Anode Materials for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are emerging as a viable alternative to lithium-ion batteries, reducing the reliance on scarce transition metals. Converting agricultural biomass into SIB anodes can remarkably enhance sustainability in both the agriculture and battery industries. However, the complex and costly synthesis and unsatisfactory electrochemical performance of biomass-derived hard carbon have hindered its further development. Herein, we employed a hydrothermally assisted carbonization process that converts switchgrass to battery-grade hard carbon capable of efficient Na-ion storage. The hydrothermal pretreatment effectively removed hemicellulose and impurities (e.g., lipids and ashes), creating thermally stable precursors suitable to produce hard carbon via carbonization. The elimination of hemicellulose and impurities contributes to a reduced surface area and lower oxygen content. With the modifications, the initial Coulombic efficiency (ICE) and cycling stability are improved concurrently. The optimized hard carbon showcased a high reversible specific capacity of 313.4 mAh g-1 at 100 mA g-1, a commendable ICE of 84.8%, and excellent cycling stability with a capacity retention of 308.4 mAh g-1 after 100 cycles. In short, this research introduces a cost-effective method for producing anode materials for SIBs and highlights a sustainable pathway for biomass utilization, underscoring mutual benefits for the energy and agricultural sectors.

Pseudocapacitive contribution in sulfur-doped porous carbon nanosheets enables high-performance sodium-ion storage

Sulfur-doped carbon materials have sparked considerable attention as the anodes for sodium-ion batteries (SIBs) due to their relatively high reversible specific capacity and excellent pseudocapacitive effect. However, the content of sulfur dopants in carbon materials is usually limited and an efficient doping strategy is urgently imperative to date. Herein, a space-confined doping strategy is proposed to fabricate porous carbon nanosheets with high sulfur dopant content by using low-cost pitch as a precursor with the help of sodium thiosulfate (Na2S2O3). The thermostable nano-MgO used in this system can occupy the specific space during pitch decomposition to induce the formation of hierarchical carbon nanosheets. Interestingly, such a space-confinement effect of nano-MgO is able to enlarge the accessible contact area of reactants and inhibit the loss of sulfur from Na2S2O3, thus significantly increasing sulfur dopant content within carbon frameworks. The optimized sulfur-doped carbon nanosheets (S-PCNs-2) with a high sulfur content of about 20.56 wt% as anode for SIBs delivers an ultrahigh pseudocapacitive contribution of 92.55 % at 5 mV s−1 and thus enable a desirable specific capacity of 428.6 mAh g−1 at 0.1 A g−1 with a high initial Coulombic efficiency of 84.9 % and superior rate performance of 380.6 mAh g−1 at 5 A g−1. Furthermore, a long cycling lifespan with a capacity retention of 88 % after 1000 charge/discharge cycles can be achieved for the S-PCNs-2 anode. This work provides a simple yet efficient doping approach to fabricate carbon anodes with high heteroatom contents for SIBs.

Topochemical behavior of ferrocene embedded in V2O5·nH2O with weak hydrogen bonding enhancing ammonium-ion storage

Aqueous ammonium ion batteries (AAIBs) are garnering increasing attention due to their utilization of abundant resources, cost-effectiveness, safety, and unique energy storage mechanism. The pursuit of high-performance cathode materials has become a pressing issue. In this study, we propose and synthesize ferrocene-embedded hydrated vanadium pentoxide (Fer/VOH) for implementation in AAIBs. The inclusion of ferrocene serves to expand the interlayer spacing, mitigate interlayer forces, and introduce the electron-rich environment characteristic of ferrocene. This augmentation facilitates the creation of additional oxygen vacancies, substantially enhancing the capacity and efficiency of ammonium ion storage. Notably, our investigation reveals that the incorporation of ferrocene attenuates the hydrogen bonding interactions associated with ammonium ions, rendering them more amenable to the interlayer embedding and release processes. Building upon these advantages, Fer/VOH exhibits a specific capacity of 313 mAh/g at a current density of 0.2 A/g, representing the highest reported performance among vanadium oxides utilized in AAIBs to date. Even after 2000 charge/discharge cycles at a current density of 2 A/g, Fer/VOH maintains a reversible specific capacity of 89 mAh/g, with a capacity retention rate of 54.8%. This study confirms the viability of Fer/VOH as a cathode material for AAIBs and offers a novel approach to enhancing the electrical conductivity and diminishing the hydrogen bonding forces in vanadium oxide intercalation through the embedding of electron-rich species and positronic groups.