Good Cycling Research Articles

Development of activated carbon by bio waste material for application in supercapacitor electrodes

Green nanotechnology is now emerging to address society's global sustainability issues by recycling numerous industrial and bio-wastes to produce functional carbonaceous nanomaterials like biochar, 2D graphene, graphene oxide, carbon nanotube (CNT), activated carbon (AC), etc. In this study, we have synthesized AC via the hydrothermal decomposition approach of the walnut shell under high temperature and pressure in a hydrothermal autoclave at temperature ranges from 200 to 250 ℃. The synthesized AC has a high specific surface area of 408.8 m2/g. It has an excellent specific capacitance of 204F/g at 1 A/g of current density with good cyclability up to 10,000 cycles.

Heterostructures of MXenes and transition metal oxides for supercapacitors: an overview.

MXenes are a large family of two dimensional (2D) materials with high conductivity, redox activity and compositional diversity that have become front-runners in the materials world for a diverse range of energy storage applications. High-performing supercapacitors require electrode materials with high charge storage capabilities, excellent electrical conductivity for fast electron transfer, and the ability of fast charging/discharging with good cyclability. While MXenes show many of these properties, their energy storage capability is limited by a narrow electrochemically stable potential window due to irreversible oxidation under anodic potentials. Although transition metal oxides (TMOs) are often high-capacity materials with high redox activity, their cyclability and poor rate performance are persistent challenges because of their dissolution in aqueous electrolytes and mediocre conductivity. Forming heterostructures of MXenes with TMOs and using hybrid electrodes is a feasible approach to simultaneously increase the charge storage capacity of MXenes and improve the cyclability and rate performance of oxides. MXenes could also act as conductive substrates for the growth of oxides, which could perform as spacers to stop the aggregation of MXene sheets during charging/discharging and help in improving the supercapacitor performance. Moreover, TMOs could increase the interfacial contact between MXene sheets and help in providing short-diffusion ion channels. Hence, MXene/TMO heterostructures are promising for energy storage. This review summarizes the most recent developments in MXene/oxide heterostructures for supercapacitors and highlights the roles of individual components.

Magnetocaloric materials for hydrogen liquefaction

<p>The expected energy transition to hydrogen gas as a greener energy vector has revived the interest in magnetic refrigeration at the cryogenic range, specifically between 20 and 80 K, with the vision to develop a new generation of hydrogen gas liquefiers. From the materials science point of view, the search for magnetocaloric materials containing mainly non-critical elements with a significant response in that temperature range, together with good cyclability and stability, is a challenging task. Given the increasing interest of the research community on this topic, we aim to establish a comprehensive catalog of the magnetocaloric compounds characterized so far, to be used as a starting point for further research. For this purpose, a systematic outlook of the state of the art is presented here, with the analysis and classification of more than 400 cryogenic magnetocaloric materials, divided into five large families according to their physicochemical properties. Moreover, we provide detailed information about their magnetocaloric properties, magnetic behavior, and transition characteristics together with criticality, which will facilitate the future search for optimal compounds.</p>

Mixture of an ionic liquid and organic solvent at graphene: interface structure and ORR mechanism.

Aprotic lithium-oxygen batteries are attracting the attention of the scientific community due to their outstanding theoretical performance, which, however, still has not been achieved in practice. One of the promising directions for improving the stability of Li-O2 batteries is electrolyte design, which would provide good cyclability, inhibition of parasitic processes, and high energy density. In recent years, there has been progress in the use of ionic liquids in the composition of the electrolyte. The present work reveals possible explanations of the influence of the ionic liquid on the mechanism of the oxygen reduction reaction by the example of a combined electrolyte from an organic solvent DME and an ionic liquid Pyr14TFSI. Molecular dynamics modelling of the interface between a graphene electrode and an organic solvent DME with a variable volume fraction of the ionic liquid shows the influence of the electrolyte structure at the interface to the kinetics on the adsorption and desorption stages of oxygen reduction reaction reactants. The obtained results suggest the promotion of a two-electron oxygen reduction reaction mechanism through the formation of solvated O22-, which may explain the reduced recharge overpotential reported in experiments.

A ternary MOF derived single crystalline LiNi1/3Mn1/3Co1/3O2 as high-voltage cathodes for lithium-ion batteries

Single-crystal NCMs show properties of good cyclability and high safety, and considers as promising cathode materials for next generation lithium batteries. But industrial production of single-crystal NCMs should overcome problems of lengthy production steps, high production costs and poor consistency. In this work, a Ni-Co-Mn ternary MOF has been developed for NCM cathode materials preparation. The MOF derived precursors show high activity and can be used to prepare single-crystal NCM111 (SC-NCM) in a regular sintering process. As-prepared SC-NCM cathode materials show an average particle size of 400 nm, reveal a polyhedral structure with smooth surface, and can be applied as a high-voltage cathode with excellent cyclability and high specific capacities. Specifically, it is delivery a high discharge capacity of 172 mAh g−1 and maintains 156 mAh g−1 after 50 cycles in a large potential range of 2.8–4.6 V at a high current of 1 C; it also reveals a good capacity retention of 88.3 % after 600 cycles. The enhanced electrochemical performance can be attributed to the SC-NCM reveals a good microstructural stability, which prevents the unexpected structural degradation and microcrack generation during battery cycling. This work provides a new method to synthesis the high-quality single-crystal NCM materials with good electrochemical performance.

Nanoengineering of MgSO4 nanohybrid on MXene substrate for efficient thermochemical heat storage material

2D MXene nanohybrid is a next-generationenergy-storage material. Here, we demonstrate a novel thermochemical heat storage material using magnesium sulfate heptahydrate/titanium carbide and MXene (MgSO4/Ti3C2Tx) with improved hydration/dehydration enthalpy, superior thermal conductivity, good cyclic ability, maximum water sorption performance, and larger thermal energy conversion. The TG-DSC fitted with a Wetsys flow humidity generator shows outstanding thermal performance and larger hydration for MgSO4/Ti3C2Tx (1963 J/g) and dehydration (1861 J/g) enthalpies with 5 % fluctuation as compared to pure MgSO4 (38 %). The cyclicability results showed that MgSO4/MXene has good stability of TCMs across several charging/discharging cycles (up to 20 cycles), confirming that the MXene matrix avoids hydrated salt agglomeration and displays an average of 12 % fluctuation. This illustrates that prepared composites potentially improve storage performance. The MgSO4/Ti3C2Tx nanohybrid exhibit a better radiation absorption and 45 % longer backup than the pristine MgSO4 salt. TEM study revealedthat maximum salt contents can be located in the interlayer gaps, predicted sheets thickness of the MgSO4/MXene layer to be 16 Åand the Ti3C2Tx layers to be 7.3 Å. Nanohybrid has stronger water sorption than MgSO4 due to MXene nanosheets larger interlayer gaps. The results conclude that the resultant MgSO4/MXene has excellent long-term thermal energy storage, photo-to-thermal conversion and larger water sorption performance. The study validates the effectiveness of nanohybrid material as a promising candidate for thermochemical heat storage applications and set to pave the way to explore other hybrid systems to improve the efficiency of thermochemical energy storage systems.

A visible multi-response electrochemical sensor based on cellulose nanocrystals

Cellulose nanocrystals (CNCs), a renewable material extracted from plants, algae, and bacteria, form iridescent films with chiral nematic order. Here, we report stimuli-responsive CNC / polyaniline (PANI) composite films for use in optical and electrochemical sensing. CNC-PANI and CNC-glucose-PANI films with bright structural color were obtained by an optimized self-assembly process. The films responded to humidity, pH and organic solvents with a change in the reflection wavelength, change in visible structural color, and changes in conductivity. A two-layer, conductive CNC-PANI film was prepared and incorporated into a circuit, where it could respond to stimuli with a change in color and increased conductivity. Moreover, a PANI electrochromic device (ECD) with CNC films was fabricated for information encryption. With voltages up to 1.5 V, the color of the ECD changed from green to blue within 1 s, and the CNC pattern hidden inside appeared with good cyclability. The ECD can also be used for anti-counterfeiting due to the chiral nematic CNC pattern. This novel iridescent CNC-PANI film demonstrates the potential of visible electrochemical multi-sensing using natural, sustainable materials.

Geopolymer composite spheres derived from graphene-modified fly ash/slag: Facile synthesis and removal of lead ions in wastewater

Geopolymer composite spheres derived from potassium-activated graphene-modified slag/fly ash powder were produced in a polyethylene glycol (PEG 400) solvent. The effect of graphene type (graphene oxide (GO) and few-layered graphene (GNP)) on the pore structure and lead ions (Pb2+) removal performance of the spheres were evaluated. The results showed that the composite spheres modified with GOs (0.1–0.4 wt%) and GNPs (1–4 wt%) could be spheroidized with an improved performance to adsorb Pb2+ in solution. The graphene-containing spheres reached a maximum BET surface area of 68.85 m2/g. Pseudo-second-order and Langmuir isotherm models could express the adsorption process, which was controlled by both monolayer adsorption and chemisorption. The obtained spheres also showed high adsorption capacities for Ni2+, Cu2+, Zn2+ and Cd2+ ions. Chemical, physical, electrostatic, ion exchange and cation-π interaction were attributed to the adsorption mechanism of the spheres. The spheres showed good cycling ability compared to those without graphene, which had potential application in heavy metal wastewater treatment.

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.

All-in-One Electric Double Layer Supercapacitors Based on CH3NH3PbI3 Perovskite Electrodes.

Supercapacitors (SCs) are widely used energy storage devices in various applications that require instantaneous power supply and fast response times; however, the challenge for achieving high performance demands the continuous development and tailoring of electrode materials. Organic-inorganic halide perovskites (OIHPs) have recently received significant attention in electrochemical energy storage and conversion applications due to their unique properties including high charge carrier mobility, high mixed (electronic-ionic) conductivity, and presence of large oxygen vacancies. This study presents the fabrication and use of OIHPs based on methyl-ammonium lead iodide (CH3NH3PbI3) and its Co2+- and Bi3+-substituted derivatives (CH3NH3Pb1-x Co x I3 and CH3NH3Pb1-x Bi x I3, respectively, where x = 0.1) as electrodes for SCs. SC devices were constructed symmetrically by sandwiching the synthesized electrode materials in a quasi-solid-state electrolyte between two TiO2-coated FTO glasses. We discussed the optimization parameters (i.e., A-site doping, B-site doping, and controlling the stoichiometry of the anion and cation) to improve the electrochemical performance of the fabricated SCs. Furthermore, the effects of substitution ions (Co2+ and Bi3+) on the charge-discharge performance, energy and power density, defects, crystallinity, and microstructure were demonstrated. Electrochemical performances of the electrodes were analyzed by using CV, EIS, and GCPL techniques. The highest power density of 934.6 W/kg was obtained for Bi-substituted perovskite electrodes. Fabricated SC devices show good cyclability with 97.2, 96.3, and 86.6% retention of the initial capacitances after 50 cycles for pure, Co2+-substituted, and Bi3+-substituted perovskite electrodes, respectively.

Photocatalytic Degradation of Tetracycline by Supramolecular Materials Constructed with Organic Cations and Silver Iodide

Photocatalytic degradation, as a very significant advanced oxidation technology in the field of environmental purification, has attracted extensive attention in recent years. The design and synthesis of catalysts with high-intensity photocatalytic properties have been the focus of many researchers in recent years. In this contribution, two new supramolecular materials {[(L1)·(Ag4I7)]CH3CN} (1), {[(L2)·(Ag4I7)]CH3CN} (2) were synthesized by solution volatilization reaction of two cationic templates 1,3,5-Tris(4-aminopyridinylmethyl)-2,4,6-Trimethylphenyl bromide (L1) and 1,3,5-Tris(4-methyl pyridinyl methyl)-2,4,6-trimethylphenyl bromide (L2) with metal salt AgI at room temperature, respectively. The degradation effect of 1 and 2 as catalyst on tetracycline (TC) under visible light irradiation was studied. The results showed that the degradation of TC by 1 was better than that by 2 and both of them had good stability and cyclability. The effects of pH value, catalyst dosage, and anion in water on the photocatalytic performance were also investigated. The adsorption kinetics fit the quasi-first-order model best. After 180 min of irradiation with 1, the degradation rate of TC can reach 97.91%. In addition, the trapping experiments showed that ·OH was the main active substance in the photocatalytic degradation of TC compared with ·O2− and h+. Because of its simple synthesis and high removal efficiency, catalyst 1 has potential value for the treatment of wastewater containing organic matter.

Electrochemically Induced Borate Allotropes for Expedite Charge Transfer in Lithium‐Ion Batteries and Hydroxyl Ion Capture Activity in Flexible Pseudocapacitor

AbstractDespite lithium‐ion battery (LIB) and supercapacitor materials have gone through numerous enhancements, achieving high energy density as well as power density together is still a dream for the industries. In this scenario, herein we report, boric acid coated α−MnO2 anode with 1288 mAh g−1 at 0.1 C at the initial cycle and of an average discharge capacity of 570 mAh g−1 at 0.1 C over 20 cycles, high‐rate capability and 100 % Coulombic efficiency after 60 cycles for LIB. The Li+ diffusion coefficient estimated from GITT and EIS measurements reveals that the H3BO3 coated α−MnO2 electrode has superior Li‐ion kinetics ( ∼10−10 cm2 s−1) than bare α−MnO2. Coin cells with boric acid coated α−MnO2 electrode are able to power up red and blue LEDs continuously for about 24–32 hours. The ex‐situ investigations reveal an interesting self‐assembled active electrode‐electrolyte interfacial bridging Li4B2O5 layer formation. This significant active layer allows free migration of lithium ions across interface that leads to good cyclability. In flexible supercapacitor, the boric acid coated α−MnO2 yields excellent cyclability over 500 cycles with specific capacitance of 35 F g−1 at 1 A g−1 and further 200 cycles at 30° acute angle with 21 F g−1 at 1 A g−1. The research overthrows the significance of boric acid in conversion reactions for active interfacial bridging layer in LIB and hydroxyl ion capturing agent in flexible supercapacitor.

Ionic liquid additive enabling anti-freezing aqueous electrolyte and dendrite-free Zn metal electrode with organic/inorganic hybrid solid electrolyte interphase layer

• [BMIM]OTF ionic liquid is used as the electrolyte additive for zinc-ion batteries. • The modified electrolyte can offer very large ionic conductivity at –40°C. • The [BMIM]OTF enables the formation of an organic/inorganic hybrid SEI layer. • The Zn deposition process is homogenized and parasitic side reactions are inhibited. • The full battery with [BMIM]OTF exhibits excellent performances even at −30°C. Benefiting from intrinsic safety, low cost, and competitive energy density, aqueous zinc-ion batteries (AZIBs) have attracted tremendous research interest, whereas suffering from low stability of Zn metal anode in aqueous electrolytes. Herein, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTF), a water-soluble ionic liquid with very low melting point, is used as the electrolyte additive. The addition of [BMIM]OTF only slightly influences the ionic conductivity of 3 M Zn(OTF) 2 aqueous electrolyte at room temperature, while considerably improving the tolerance to low temperatures. This additive is also found to be preferentially adsorbed on the Zn electrode, tune the solvation sheath of hydrated Zn 2+ ions, reduce the corrosion activity of Zn electrode, and enable the formation of an organic/inorganic hybrid solid electrolyte interphase (SEI) layer. Such SEI layer is zincophilic and hydrophobic, thereby decreasing the nucleation overpotential of Zn plating, enhancing the interfacial charge transfer kinetics, homogenizing the Zn deposition behavior, and inhibiting parasitic side reactions. With the [BMIM]OTF-modified electrolyte, the Zn//Zn symmetric cell offers good cyclability even under extremely large areal capacity of 25 mAh cm −2 . And the assembled AZIB with an Al-vanadate cathode material exhibits excellent performances even at −30°C. This work provides new insights into stabilizing aqueous batteries.

Free-standing vanadium oxide hydration/reduced graphene oxide film for ammonium ion supercapacitors

Aqueous ammonium-ion energy storage systems have recently gained continuous attention owing to the advantages of sustainability and environmental-friendliness in the grid-scale application. However, ammonium-ion supercapacitors are still in their infancy, and it is of great challenge in developing suitable materials for application in wearable energy storage devices. Herein, we develop a vanadium oxide hydration (V2O5·nH2O)/reduced graphene oxide (rGO) composite film (denoted as VGF) as a free-standing paper-like electrode for ammonium-ion storage, where V2O5·nH2O shows an expanded interlayer spacing and is sandwiched by rGO through chemical bonds. As a result, the designed VGF exhibits a capacitance of 600F·g−1 at 0.2 A·g−1 and good cyclability of over 10,000 cycles with a retention of 93 % using PVA/NH4Cl gel electrolyte. Meanwhile, the ammonium-ion storage mechanism in VGF electrode is further verified to be dominated by the intercalation pseudocapacitance and electric double-layer capacitance. Furthermore, the quasi-solid-state symmetric supercapacitor (SSC) has been also assembled to assess the feasibility of practical applications in wearable devices. As expected, the SSC possesses an areal capacitance of 241 mF·cm−2 at 0.1 mA·cm−2 (0.82 Wh·m−2 at 0.09 W·m−2) and an excellent cyclability of 20,000 cycles with a retention of 92 %, which is comparable to that achieved in the vanadium oxides powder-made electrodes and the SSC made of. Together with the excellent flexibility and feasibility of parallel/series combination, the VGF SSC devices shows great possibility for the applications in wearable devices, which further proves the great potential of this designed VGF free-standing electrode for ammonium-ion storage.

Scalable fabrication of Bi@N-doped carbon as anodes for sodium/potassium-ion batteries with enhanced electrochemical performances

Metallic bismuth as a promising anode for alkali metal-ion batteries has attracted great attentions because of superb volumetric capacity (3800 mA h cm−3) and suitable working voltage plateaus (∼0.5 V). However, Bi anode suffers from large volume change during repeated cycling, resulting in poor cycle performance. In this contribution, Bi nanoparticles embedded in N-doped carbon materials (Bi@N-C) are designed and fabricated by one-step pyrolysis method. Thanks to the synergistic effects of Bi nanoparticles and the N-doped carbon framework, the elaborately designed Bi@N-C can not only reduces the ion/electron diffusion pathways and enhances the reaction kinetics, but can also availably inhibits the agglomeration of Bi particles, and effectively alleviates the volume fluctuation. As an anode material, the Bi@N-C exhibits advanced rate capability (219 mA h g−1 at 5 A g−1) and excellent stable cycle ability (307 mA h g−1 at 1 A g−1, after 400 cycles) in sodium-ion batteries. Furthermore, the Bi@N-C anode also exhibit good stable cycle ability (240 mA h g−1 at 1 A g−1, after 70 cycles) in potassium-ion batteries. This study provides a facile and environmentally friendly way for fabricating high performance Bi anodes towards SIBs and PIBs.

Magnesium doped LiNixMnyCozO2 cathode- structural properties

High energy density and low-cost lithium-ion batteries (LIBs) are the most efficient energy storage devices. Moreover, LIBs with nickel-rich LiNixMnyCozO2 (N-NMC) cathodes provide an attractive candidate for electric vehicle applications due to their performance metrics. In the N-NMC, each element offers different properties, including high capacity, good cycling, and excellent conductivity. But, ion mixing, metal-ion dissolution, oxygen loss, etc., on the cathode surface cause severe effects on the electrode. Consequently, magnesium (Mg) doping on the NMC cathode eliminates these drawbacks, ensures high thermal stability, inhibits cation mixing, and prevents irreversible capacity loss. Additionally, the low-cost co-precipitation method aids in the highly efficient synthesizing of homogeneous Mg-doped NMC cathode materials. Here, X-ray diffraction (XRD) confirms the phase and crystallinity of the materials, with I(003)/I(104) ratios of 1.4942, 0.9790, and 0.9148 for NMC, NMC1, and NMC2. The morphology of the layered pristine and doped NMC has been detected using a field emission scanning electron microscope (FESEM). Raman spectra determine the crystal chemistry of layered transition metals, while Fourier Transform Infrared Spectroscopy (FTIR) detects the vibration spectra of a substance. Based on these results, an improved N-NMC cathode may represent the best electrode material for energy storage devices.

Design of B, P co-doped CoNi bimetallic for boosting supercapacitor performance: Effect of boronation and phosphorization order

The exploration of high-efficiency electrodes is urgent for energy conversion and storage devices. In this work, CoNiBP nanosheets were fabricated by a successive method which is facile and cost-effective. The nanosheet-like structure of CoNiBP enables high exposure of active sites and fast transport of ions and electrons. In addition, the synergistic effect of B and P strengthens the electrochemical performance by tuning the electronic structure of active sites. The CoNiBP electrode exhibits a high specific capacity of 870.8 C g−1 at 1 A g−1 with excellent rate capability and stability. Moreover, the assembled CoNiBP//AC asymmetric supercapacitor (ASC) device delivered an ultrahigh energy density of 71.7 Wh kg−1 at 0.8 kW·kg−1 with good cyclability (∼100% retention of original capacity after 12 000 cycles). With such superior electrochemical performance, CoNiBP is a promising material to be used as electrode in supercapacitors.

Influence of the Composition and Testing Modes on the Electrochemical Performance of Li-Rich Cathode Materials.

Li-rich oxides are promising cathode materials for Li-ion batteries. In this work, a number of different compositions of Li-rich materials and various electrochemical testing modes were investigated. The structure, chemical composition, and morphology of the materials synthesized were studied by XRD with Rietveld refinement, ICP-OES, and SEM. The particle size distributions were determined by a laser analyzer. The galvanostatic intermittent titration technique and galvanostatic cycling with different potential limits at various current densities were used to study the materials. The electrochemical study showed that gradual increase in the upper voltage limit (formation cycles) was needed to improve further cycling of the cathode materials under study. A comparison of the data obtained in different voltage ranges showed that a lower cut-off potential of 2.5 V (2.5-4.7 V range) was required for a good cyclability with a high discharge capacity. An increase in the low cut-off potential to 3.0 V (3.0-4.8 V voltage range) did not improve the electrochemical performance of the oxides and, on the contrary, considerably decreased the discharge capacity and increased the capacity fade. The LMR35 cathode material (Li1.149Ni0.184Mn0.482Co0.184O2) demonstrated the best functional properties among all the compositions studied.

Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 enabled PEO-based solid composite electrolyte with high lithium ion transference number and cycling stability

Solid polymer electrolytes (SPEs) have attracted much attention because of their potential in improving energy density and safety. Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 (LLZVO) was synthesized by high-temperature annealing, and formed a composite electrolyte with polyethylene oxide (PEO). Compared with pure PEO electrolyte membrane, the composite electrolyte membrane exhibited better ionic conductivity (30 °C: 3.2 × 10−5 S cm−1; 80 °C: 3.6 × 10−3 S cm−1). The combination of LLZVO was beneficial to improve the lithium ion transference number (tLi+) of SPE, which was as high as 0.81. The Li/SPE/LiFePO4 battery shows good cycling ability, with a specific capacity of 142 mAh g−1 after a stable cycle of 150 cycles. Meanwhile, the symmetrical lithium battery with composite electrolyte can work continuously for 1200 h without short circuit at the current density of 0.1 mA cm−2 at 50 °C, and the capacity is 0.176 mAh. Vanadium doped ceramic matrix LLZVO as an active ionic conductor, improved the overall performance of solid electrolyte.

Subnano-sized tellurium@nitrogen/phosphorus co-doped carbon nanofibers as anode for potassium-based dual-ion batteries

Tellurium (Te) is a high-volumetric-capacity and high-rate electrode material for potassium-ion (K+) storage. However, there is a lack of knowledge about the nanostructure design of electrode and detailed redox process of tellurium. Herein, we fabricated subnano-sized (<1 nm) tellurium encapsulated into nitrogen, phosphorus-codoped porous carbon nanofibers (Te@N,P-codoped PCNFs). Single-atom and small-molecule tellurium allotropes can be first identified within hierarchical porous carbon through the space confinement of micropores and the chemical bonding effect. A multi-step transformation process for K+ storage is disclosed by experimental and theoretical approaches, where tellurium is firstly converted into K2Ten (n = 5 ∼ 7), then reduced to K2Te3/K2Te2, and eventually transformed into K2Te. Importantly, heteroatoms codoping facilitates tellurium immobilization and K2Te adsorption to avoid their detachment from electrode, and meanwhile, the space confinement of micropores effectively alleviates the volume change. This well-designed electrode exhibits high capacity of 2023.13 mAh cm−3 after 700 cycles at 0.5 C and superior cycling performance for 1500 cycles at 5.0 C, which endows graphite cathode-based dual-ion batteries with good cyclability and high energy density of 191.6 Wh kg−1 (based on the total mass of the anode and cathode). Our work demonstrates the feasibility of atomically dispersed tellurium through the structure engineering, and provides new insights for the manipulation of tellurium chemistry.