Electrolyte Diffusion Research Articles

Binder-Free Flexible Chickpea Pod Derived Activated Carbon-Carbon Nanofiber Composite for Supercapacitor Application

In the present study, a novel carbon-carbon composite electrode was prepared by embedding activated carbon derived from chickpea pods and evaluated its potential as an electrode for supercapacitors. A simple, single-step electrospinning technique was used for the synthesis of activated carbon-carbon nanofiber composite. The synthesized activated carbon-carbon nanofiber composite electrode is flexible and binder-free with high specific surface area, micro and mesopores, interconnected fiber-to-flake morphology and possess high graphitization. Additionally, rapid electrolyte diffusion has resulted in a low charge transfer resistance due to interconnected morphology. In 6 M KOH electrolyte, composite binder-free electrode shows a specific capacitance of 147 F g−1 at 0.5 A g−1 compared to activated carbon (AC) electrodes that showed a specific capacitance of 120 F g−1 at 0.5 A g−1. It exhibits an energy density of 13 Wh k g−1 at 0.366 W k g−1 power density. It also showed impressive cyclic stability by retaining 93.5% of initial capacitance till 1200 cycles at 1 A g−1. Overall, the study presents an easy-to-use, low-cost, eco-friendly, and flexible electrode for supercapacitors that is free of binder.

Construction of bimetallic phosphide nanostructures with in situ growth, reduction, and phosphidation of ultra-thin graphene layers as highly efficient catalysts towards the OER.

We present a novel approach for the in situ growth of bimetallic silicate onto ultrathin graphene, followed by in situ reduction and phosphorization to obtain uniformly dispersed bimetallic phosphides (rGO@FeNiP/rGO@FeCoP) on graphene layers. Unlike the traditional simple composites of single-metallic phosphides and carbon materials, the bimetallic synergy of rGO@FeNiP/rGO@FeCoP obtained through in situ growth, reduction, phosphorization, and alkaline treatment exhibits a large surface area, more nanopores and defects, and more active sites, facilitates electrolyte diffusion and gas release, accelerates electron transfer and enhances electrocatalytic oxygen evolution reaction (OER) performance. Furthermore, the continuous carbon layer architecture surrounding FeNiP/FeCoP provides structural support, improving catalyst stability. We have investigated the effect of different proportions of bimetals on electrocatalytic performance, providing a rational design and synthesis strategy for carbon-based bimetallic phosphides as a promising electrocatalyst for the OER.

A novel binder-free cathode catalyst Cu@NCNF/CP with three-dimensional self-supporting structure for Li-CO2 battery

The Li-CO2 battery is an emerging energy storage device that has garnered significant attention due to its high theoretical energy density and remarkable CO2 capture ability. However, the low reaction activity of Li2CO3 formation and decomposition may result in large overpotentials and poor cycling performance. In this work, a novel three-dimensional self-supporting high-performance cathode catalyst (Cu@NCNF/CP) was prepared. The Cu@NCNF/CP cathode catalyst is composed of Cu nanoparticles loaded on nitrogen-doped carbon nanotube fibers (NCNF) deposited on carbon paper (CP). The three-dimensional interconnected self-supporting structure of Cu@NCNF/CP eliminates the need for binders and can facilitate efficient electrolyte diffusion and electron transfer. Moreover, the nitrogen doping introduces enrichment active sites, and boosts the CO2 reduction reaction (CO2RR) activity, while the uniformly loaded Cu nanoparticles facilitate the adsorption and precipitation of CO2 molecules, thereby playing a crucial role in enhancing the electrocatalytic activity of the CO2 evolution reaction (CO2ER). Importantly, the Li-CO2 battery utilizing Cu@NCNF/CP as a cathode catalyst exhibits a large discharge capacity of 10.59 mAh cm−2 at a current density of 0.05 mA cm−2. When the cutoff capacity is limited to 0.15 mAh cm−2, the first-cycle overpotential is merely 1.28 V, and the cycle life can reach 1140 h due to the high reversibility of the Li2CO3 formation and decomposition. The successful application of a three-dimensional self-supporting Cu@NCNF/CP cathode catalyst in Li-CO2 battery systems introduces a novel concept for developing high-performance transition metal-based catalysts.

Natural polymers as sustainable precursors for scalable production of N/SOx doped carbon material enabling high‐performance supercapacitors

AbstractNatural polymers‐based carbon electrodes have gained significant research attention for next‐generation portable supercapacitors. Herein, present an environmentally benign and novel approach for the synthesis of N/S‐Ox carbon material derived from natural polymers on gram scale. By capitalizing the synergistic effect of sulfonated lignin and amino‐containing chitosan, this methodology produces a straightforward, low‐budget, and scalable process. The incorporation of sulfonate motifs from lignin contributes to the formation of C‐SOx moieties and multi‐porous architecture with a high surface area. Simultaneously, amino groups in chitosan induce nitrogen doping, enhancing conductivity, and wettability. The resulting N/SOx carbon material exhibits a micro/meso‐porous architecture, facilitating electrolyte diffusion, and demonstrating improved rate capability and pseudocapacitance via Faradaic redox reactions. The N/SOx carbon material showcases notable capacitance (392 F g−1 at 1 Ag−1) as compared with the reported carbon materials form biomass and outstanding cyclic stability (94.8% retention after 5000 cycles). By optimizing various chitosan mass ratios, the most effective N/SOx carbon material SNACM = S/N‐doped activated carbon material (SNACM‐2) was produced using a lignin: chitosan sample ratio of 1:2 for symmetric supercapacitors. Furthermore, the quasi‐solid‐state symmetric supercapacitors based on SNACM‐2 exhibit an excellent specific capacitance of 142 F g−1 at 1 A g−1, coupled with outstanding flexibility. The SNACM‐2 demonstrates a high‐energy density of 9.8 W h kg−1 at a power density of 0.5 kW kg−1. This study presents a successful strategy for transforming low‐valued, eco‐friendly natural polymers into renewable, high‐performance carbon materials for supercapacitors.image

Bimetallic-Coordinated Covalent Triazine Framework-Derived FeNi Alloy Nanoparticle-Decorated Coral-Like Nanocarbons for Oxygen Electrocatalysis.

It is highly desirable to fabricate transition bimetallic alloy-embedded porous nanocarbons with a unique nanoarchitecture for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in rechargeable zinc-air batteries. In this work, we introduce a template-assisted in situ alloying synthesis of FeNi alloy nanoparticle-decorated coral-like nanocarbons (FeNi-CNCs) as efficient OER/ORR dual-functional electrocatalysts. The present materials are produced through polycondensation of a covalent triazine framework (CTF), the coordination of Ni and Fe ions, and sequential pyrolytic treatment. Through the pyrolysis process, the nanolamellar FeNi-CTF precursors can be facilely converted into FeNi alloy nanoparticle-decorated nanocarbons. These nanocarbons possess a distinctive three-dimensional (3D) coral-like nanostructure, which is favorable for the transport of oxygen and the diffusion of electrolyte. As a result, FeNi-CNC-800 with the highest efficiency exhibited remarkable electrocatalytic performance and great durability. Additionally, it also can be assembled into rechargeable zinc-air batteries that can be assembled in both liquid and solid forms, offering a superior peak power density, large specific capacity, and outstanding reusability during charging/discharging cycles (e.g., 5160 charging-and-discharging cycles at 10 mA cm-2 for the liquid forms). These traits make it a highly promising option in the burgeoning field of wearable energy conversion.

Sub-microscale 3D printing based on cold-constrained local electrodeposition

ABSTRACT Locally confined electrodeposition of precursors in liquid is one of the most effective approaches for additive manufacturing of metal microstructures. However, reported data were overwhelmingly obtained at the micrometer scale, whereas sub-microscale and nanoscale microstructures are of interest in electromagnetic or optical fields. In this paper, we propose a cold-constrained local electrodeposition (CCLE) technique to address the issue that locally confined electrodeposition of precursors in liquid is challenging in the fabrication of sub-microscale three-dimensional microstructures. Microstructure printing is conducted via locally confined electrodeposition by a pipette with a sub-microscale opening to deliver electrodeposition electrolyte in a supporting electrolyte. The electrolytes are cooled to 5 °C, which constrains the large-scale diffusion of the electrodeposition electrolyte and significantly reduces the electrodeposition area. It is found that the proposed CCLE technique can print sub-microscale (minimum size is low to 290 nm) structures, which have highly uniform deposits, smooth surfaces and high strength.

Sandwich-type CoSe2-CNWs@NG as host for lithium-sulfur batteries with high sulfur loading, ultrahigh rate, and long lifespan

While lithium-sulfur batteries (LSBs) have tremendous potential in capacity and energy, their application in practice is limited by short cycle life, slow reaction kinetics, and underutilization of sulfur. To tackle these challenges, we have developed a multifunctional host consisting of sandwich-type CoSe2-CNWs@NG that were hydrothermally synthesized through self-assembly of CoSe2-embedded carbon nanowires (CoSe2-CNWs) with N-doped graphene (NG). Through the implementation of CoSe2-CNWs@NG as a host material, active sulfur can be effectively intercalated within the interlayer spaces of neighboring NG layers. The extensive contact area between sulfur and NG sheets facilitates rapid electron transfer, thereby maximizing sulfur utilization. N-doped graphene and polar CoSe2 provide sufficient chemisorption sites for polysulfides, while the catalytic activity of CoSe2 promotes polysulfide conversion. In addition to building a good conductivity structure for fast carrier transport and electrolyte diffusion, the sandwich structure of CoSe2-CNWs@NG physically restricts polysulfides and buffers substantial sulfur volume changes during cycling. As a result, the CoSe2-CNWs@NG/S cathode possessing high-load sulfur capacity (4.06 mg cm−2) exhibits superior cell performance at an ultrahigh rate as well as low E/S ratio. After 1000 cycles at 10 C, it achieves a remarkable reversible capacity of 314.4 mAh g−1 with an impressively low average fading rate of 0.023 % per cycle. Even at a low E/S ratio of 5 μL mg−1, the cathode exhibits remarkable performance, retaining a reversible capacity of 628.2 mAh g−1 after 150 cycles at the rate of 1 C.

Dual chemifunctional tin(IV) oxide/nanoperforated graphene interlayer as a polysulfide adsorbent for use in high-performance lithium–sulfur batteries

The development of Li–S batteries is limited by their levels of rapid capacity decay owing to polysulfide dissolution and diffusion in organic electrolytes. We addressed this critical issue by fabricating a dual chemifunctional interlayer comprising SnO2 nanoparticles and nanoperforated graphene (NPG) that could function as a polysulfide adsorbent. The synergistic effects of SnO2 and the high-density functional groups of NPG on polysulfide capture were conceptually confirmed. NPG not only supported the adsorption of Li polysulfides but also provided pathways for simple Li-ion motion within the SnO2/NPG interlayer. A cell assembled with the SnO2/NPG interlayer displayed a high rate capability and initial discharge capacity and good reversible capacity. The excellent high-rate cycling performance of the cathode could mainly be attributed to the strong chemical bonds formed between SnO2/NPG and the polysulfides, rapid electron transfer, and optimized ion diffusion pathways derived from the well-organized structure of the composite. Synthesizing dual chemifunctional interlayers using a composite of metal oxides and NPG may lead to the development of advanced Li–S batteries with numerous practical applications in the near future.

Tuning electronic structure of hedgehog-like nickel cobaltite via molybdenum-doping for enhanced electrocatalytic oxygen evolution catalysis

As a typical spinel oxide, nickel cobaltite (NiCo2O4) is considered to be a promising and reliable oxygen evolution reaction (OER) catalyst due to its abundant oxidation states and the synergistic effect of multiple metal species. However, the electrocatalytic OER performance of NiCo2O4 has always been limited by the low specific surface area and poor intrinsic conductivity of spinels. Herein, the hedgehog-like molybdenum-doped NiCo2O4 (Mo-NiCo2O4) catalyst was prepared as an efficient OER electrocatalyst via a facile hydrothermal method followed with high-temperature annealing. The Mo-NiCo2O4-0.075 with Mo doping concentration of ∼ 1.95 wt% exhibits excellent OER performance with a low overpotential of 265 mV at a current density of 10 mA·cm−2and a Tafel slope of 126.63 mV·dec-1, as well as excellent cyclingstability.The results demonstrated that the hedgehog-like structure provides Mo-NiCo2O4 with the high surface area and mesopores that enhance electrolyte diffusion and optimal active site exposure. The in-situ Raman spectra and density functional theory calculations show that the Mo cations doping improve the intrinsic conductivity of the NiCo2O4 while modulating the chemisorption of intermediates. Meanwhile, the energy barriers of *OH and O* formation decrease significantly after Mo doping, effectively facilitating water dissociation and optimizing the reaction kinetics.

MIL-100(V) derived porous vanadium oxide/carbon microspheres with oxygen defects and intercalated water molecules as high-performance cathode for aqueous zinc ion battery

The development of aqueous zinc ion battery cathode materials with high capacity and high magnification is still a challenge. Herein, porous vanadium oxide/carbon (p-VOx@C, mainly VO2 with a small amount of V2O3) core/shell microspheres with oxygen vacancies are facilely fabricated by using a vanadium-based metal–organic framework (MIL-100(V)) as a sacrificial template. This unique structure can improve the conductivity of the VOx, accelerate electrolyte diffusion, and suppress structural collapse during circulation. Subsequently, H2O molecules are introduced into the interlayer of VOx through a highly efficient in-situ electrochemical activation process, facilitating the intercalation and diffusion of zinc ions. After the activation, an optimal sample exhibits a high specific capacity of 464.3 mA h g−1 at 0.2 A g−1 and 395.2 mA h g−1 at 10 A g−1, indicating excellent rate performance. Moreover, the optimal sample maintains a capacity retention of about 89.3% after 2500 cycles at 10 A g−1. Density functional theory calculation demonstrates that the presence of oxygen vacancies and intercalated water molecules can significantly reduce the diffusion barrier for zinc ions. In addition, it is proved that the storage of zinc ions in the cathode is achieved by reversible intercalation/extraction during the charge and discharge process through various ex-situ analysis technologies. This work demonstrates that the p-VOx@C has great potential for applications in aqueous ZIBs after electrochemical activation.

Construction of coordination bond electron bridge boosting interfacial electron transfer to enhance bifunctional photocatalytic activity of TiO2/g-C3N4 heterojunction

The weak interfacial coupling of heterojunction catalysts leads to a large barrier, which inhibits interfacial electron transfer and limits the catalytic efficiency. Herein, a unique Ti-N coordination electron bridge has been designed and constructed in TiO2/g-C3N4 heterojunction with a tightly-coupled interface by using a newly designed topotactic transition and in-situ pyrolysis method. Experimental data and characterization analyses indicate that abundant stacking faults and surface oxygen vacancies change the surface atomic coordination environment and induce the formation of Ti-N coordination bond electron bridges. XPS, TA-PL probing experiment, and EPR analysis indicate a S-scheme electron transport mechanism. The synergistic effect of internal electric field and Ti-N electron bridge promote the efficient S-scheme electron transport, which facilitates the spatial separation of strong oxidizing holes and strong reducing electrons. The hierarchical nanoflower structure benefits electrolyte diffusion and reaction species adsorption. The above virtues endowed the catalyst with enhanced bifunctional photocatalytic activity for hydrogen evolution (1.89 mmol·g−1·h−1) and methyl blue degradation (0.114 min−1), which are 3.2 and 1.9 times that of the bare TiO2. This work opens a new avenue for the construction of heterojunctions and the optimization of interface carrier transfer, providing important insights for synthesizing photocatalysts with excellent activity and stability.

Dual-layer composite solid polymer electrolytes with Janus properties for interface modification of solid state lithium metal batteries

Solid polymer electrolytes are widely applied in lithium metal batteries owing to good flexibility and machinability. However, monolayer polymer electrolyte are difficult to simultaneously satisfy the interfacial contact with the cathode and Li anode. Herein, the dual-layer composite solid polymer electrolyte with polypropylene film (CSPE@PP) are designed to promote the interfacial compatibility between the solid electrolytes and electrodes. The X-ray photoelectron spectroscopy (XPS) results confirm that poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) can react with Li metal to form LiF layer, restraining the Li dendrite growth. Meanwhile, the polyacrylonitrile (PAN) antioxidant layer strengthens the contact stability between the electrolytes and the cathodes. Moreover, the PP film serves as the electrolyte's skeleton and connecting layer, enhancing the ion diffusion and mechanical strength of the solid electrolytes. As a result, the Li||CSPE@PP||Li cell is able to stably cycle over 400 h at 0.1 mA cm−2. The LFP||CSPE@PP||Li solid-state batteries deliver 141.98 mAh g−1 discharge capacity and high retention rate (91.1%) after 100 cycles at 0.1C. This work provides a viable strategy for expanding the application of composite solid polymer electrolyte (CSPE) in lithium metal batteries.

Electronic structure modification of FeWO4 through F doping for enhanced oxygen reduction performance in zinc–air batteries

Exploring efficient and stable oxygen reduction reaction (ORR) catalysts for zinc-air batteries (ZABs) holds tremendously significant. Tungsten-based materials have attracted the attention of researchers thanks to abundant resources and excellent stability. Nevertheless, due to the strong adsorption energy for O-containing intermediates, *O and *OH are difficult to desorb from tungsten-based materials during ORR. Here, an F-doping strategy was employed to construct F-doped FeWO4 species composited on a multi-dimensional N-doped carbon (F–FeWO4/NC) as the ORR catalyst for ZABs. The incorporation of F atoms into the main lattice of FeWO4 enhanced the polarity of chemical bonds in FeWO4 through hydrogen bond interactions between H2O molecules and F atoms, further enhancing the polarity and hydrophilicity of F–FeWO4/NC. These changes favored the adsorption and desorption of intermediates as well as the diffusion of electrolyte, and ultimately reduced the ORR overpotential. Therefore, the F–FeWO4/NC catalyst demonstrated excellent ORR activity (E1/2 = 0.85 V vs. RHE). Furthermore, the ZAB with F–FeWO4/NC yielded satisfactory a specific capacity of 800.2 mAh g−1, a peak power density of 173.5 mW cm−2, and charge-discharge cycling stability (over 170 h at 5 mA cm−2). This study is beneficial to improve the ORR intrinsic activity of cheap tungsten-based materials and provides theoretical guidance for their practical application in ZABs.

Influence of AC-DC-AC Cycling with Hydrostatic Pressure on Accelerated Protective Performance Test of Glass Flake Epoxy Coating

To achieve fast testing of the barrier properties of organic coatings, immersion tests, AC-DC-AC tests, and coupled tests of AC-DC-AC with hydrostatic pressure were conducted in seawater for a glass flake epoxy coating. Electrochemical impedance spectroscopy (EIS) was used to characterize the degradation processes of the coating during the tests, and the surface of the coating was analyzed using an optical microscope, scanning electron microscope (SEM), and a Fourier transform infrared spectrometer (FTIR). The results showed that periodic cathodic polarization coupled with high hydrostatic pressure can accelerate the degradation of a coating by facilitating the diffusion and uptake of electrolyte and the delamination of the coating. The coupled test method has the largest acceleration due to the synergetic effect of AC-DC-AC and hydrostatic pressure.

Effects of Heteroatom Doping and Physicochemical Character on the Electrochemical Properties of Graphene Sheets

AbstractGraphene attracted great interest in the electrochemical applications due to its stability and extremely high surface area‐to‐mass ratio. Wet chemical and electrochemical synthesis allow affordable and single to multilayer graphenes with functional groups that contribute to surface accessibility, and electrolyte diffusion. These materials also have faradaic and pseudocapacitive reaction sites which enhance the electrochemical performance while altering their capacitive nature based on reaction type and density of these sites. Therefore, heteroatom doping of graphene has been studied widely, and various outcomes, some of which have been controversial, were reported. In this study, we investigated the doping modification with multiple samples and also conduct a detailed physicochemical characterization. Oxidation‐reduction and electrochemical exfoliation methods were utilized to synthesize pristine, nitrogen‐doped, and phosphorus‐doped reduced graphene oxide as well as the phosphorus‐doped and pristine electrochemically exfoliated graphene materials. Samples have been characterized in terms of doping level, particle size, number of layers, defect density, and exfoliation homogeneity. Electrochemical measurements showed that surface wrinkling property among similarly large rGO particles (~9x) and small lateral particle size (~2x) of graphenes are effective in determination of specific capacitance (Cspecific) and capacitive characteristic of samples while heteroatom doping doesn't produce any significant change on these properties.

Introducing of WO3@NiCo2O4/rGO ternary nanocomposites as active material for high-performance supercapacitor applications

The combined materials with synergistic effects and integrate of properties of each component can be widely used for high capacity and high-power density storage devices. In this study, synthesis, energy storage ability and characterization of the novel ternary WO3@NiCo2O4/rGO nanocomposites (NWG) as active electrode materials are studied. NWG nanocomposites as high-efficiency supercapacitors material which is perfect transferring ions/electrons are constructed with multiple-step synthesis for supercapacitor application for the first time. For this purpose, at first, intertwined nanosheets of NiCo2O4 was synthesized through the hydrothermal process, afterwards, WO3 nanostructures were fabricated on the surface of NiCo2O4 via sonochemical method and finally, NWG nanocomposites were synthesized during the mild hydrothermal conditions. Towards the studying the physicochemical properties of as-fabricated NWG nanocomposites, the X-ray diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) analysis were used. Also, the electrochemical behavior of innovative NWG nanocomposites as energetic electrode materials was investigated in two and three electrode configurations for high-performance supercapacitor application. Additionally, the synergetic effect between NiCo2O4, WO3 and rGO substrates in final product (NWG) was investigated based on cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cyclic stability test. The well-designed NWG nanostructures with layered shape can acceleration the ion electrolyte diffusion and provided more redox active sites through energy storage process. The electrochemical results of the NWG nanocomposite electrodes represented a high specific capacity of 1211.75 F g−1 at a current density of 1.5 A g−1. Furthermore, the suggested electrode exhibited the great energy density of 11.92 Whkg−1, power density of 3000.8 Wkg−1 and excellent rate capability (91.51 % of capacity retention after 1000 cycles). Moreover, the specific capacitance of bare and binary nanocomposites i.e. NiCo2O4 and WO3@NiCo2O4 were investigated and compared with NWG at a current density of 2 A g−1. The results show that the specific capacitance of NWG ~1.5 times greater than NiCo2O4 and WO3@NiCo2O4 nanostructures [NiCo2O4 (498.33 F g−1), WO3@NiCo2O4 (580.33 F g−1) and NWG (917.67 F g−1)]. Remarkably, an asymmetric supercapacitor (ASC) assembled by newly-designed NWG electrode as a positive electrode and activated carbon (AC) as a negative electrode exhibited the good specific capacitance 37.2 mF g−1 at of 1.5 mA g−1. Also, the ASC device could provide energy density of 4.75 mWh kg−1 at the power density of 799.9 mWkg−1. This research recommends that NWG nanocomposites have an extraordinary potential for evolution of active electrode materials forthcoming supercapacitors in energy storage systems.

Highly stable and nanoporous Na3V2(PO4)3@C cathode material for sodium-ion batteries using thermal management

Sodium vanadium phosphate (Na3V2(PO4)3-NVP) a NASICON-type material with exceptionally high ionic conductivity is acknowledged as a potential cathode for high-performance Na-ion batteries. Herein, we report a facile sol-gel process for the preparation of NVP@C. The NVP@C produced has rhombohedral NASICON crystal structure and exhibit 3D interlink microstructure with porous morphology and carbon network. The NVP@C prepared at 900 °C display an initial discharge capacity of 99 mAhg−1 at a current density of 1C and ultralong lifespan of 1400 cycles at 10C (73 mAhg−1) with 93 % capacity retention. This superior electrochemical performance is attributed to the synergistic effect of high crystallinity, porous structure & conducting carbon network. This provides a high contact area between electrode/electrolyte, better electronic conductivity, and high mechanical strength. Additionally, this will also responsible for easy diffusion of electrolyte and speedy transport of ions which ultimately helps to accelerate the electrochemical performance. It is noteworthy that the prepared NVP@C shows highly stable electrochemical performance at higher current density (10C) with 100 % columbic efficiency. More significantly, the full cell comprising NVP@C electrodes showed capacity retention of 80 % after 500 cycles at 2C rate. These prima fascia result shows the potential of the process which provides a new understanding to design other cathode material.

Construction of 3D N-doped Ti3C2/TiO2 hollow sphere structure with superior electrochemical performance for supercapacitor

Herein, the 3D N-doped Ti3C2/TiO2 sphere structure is constructed via an innovative three-step method including the preparation of 3D Ti3C2 microspheres with PMMA as templates, the situ-growth of TiO2 nanoparticles on Ti3C2 and the subsequent annealing treatment in NH3. N element is doped in composite after annealing in NH3 to improve the transfer rate of ions and electrons, and N-doped Ti3C2/TiO2 hollow composite provides an abundant active surface for the sufficient contact between electrodes and electrolytes to enhance charge transport and electrolyte diffusion. Benefiting the unique structure feature and the synergistic effects of active materials, the N-doped Ti3C2/TiO2 electrode exhibits a high specific capacitance of 572 F g−1 at a current density of 1 A g−1 and a superior cyclic stability of 99.6% of its initial value for 9500 cycles at 10 A g−1. Based on this, a symmetric supercapacitor (SSC) based on N-doped Ti3C2/TiO2 electrode is further assembled. The SSC shows a competitive capacitance of 157 F g−1 at 1 A g−1. More importantly, the comparable energy density of 17.7 Wh kg−1 is achieved at the power density of 450 W kg−1. This work will give promising guidance for designing and fabricating the durable electrodes with excellent electrochemical behavior for practical application in future.

Combined density functional theory and molecular dynamics analyses on Lithium/Sodium ion interaction and diffusion in gel polymer electrolytes with poly-vinylidene fluoride scaffold, propylene carbonate/Ionic Liquid solvent, and perchlorate salt

Choice of a proper electrolyte is very crucial to enhance the overall performance of a metal-ion battery. In this work, dispersion corrected density functional theory and classical molecular dynamics simulations are carried out to explore the metal ion (Li+ and Na+) interaction and diffusion through polyvinylidene fluoride (PVDF)-based gel polymer electrolytes. Four types of polymer/solvent/salt electrolyte systems are investigated considering PVDF scaffold for each case, and conventionally used propylene carbonate and rarely used, albeit cheaper, ionic liquid [BMIM][ClO4] as solvent, along with metal perchlorate salts LiClO4 and NaClO4. Inter-unit interactions within the electrolyte clusters, electrolyte uptake, and electrochemical stability of the electrolytes are explained by gas-phase DFT analyses, considering the polymer/solvent/salt components in 1:1:1 molecular ratio. Diffusion of the ions and ionic conductivity of the electrolytes are explored by MD simulation referring to two different size and time scales. From the DFT-based non-bonding interaction analyses, metal ions are found to exhibit strong non-covalent interactions with the adjacent O and F atoms, where the O atoms are parts of PC and [ClO4]- ions, and F atoms are from the PVDF chains. [BMIM]+, [ClO4]-, and PVDF are found to interact through weak van der Waals type hydrogen bonds. Both DFT and MD calculations suggest that, Li+ and Na+ ions are primarily coordinated with [ClO4]- ions. Dynamics studies confirm that for PVDF/IL/salt, total ionic conductivity is predominated by [BMIM]+ and [ClO4]-, exhibiting lower metal ion diffusivity as compared to PC-containing electrolytes. For both Li- and Na-ion systems, owing to the availability of higher number of charge carriers, electrolytes containing ILs show higher ionic conductivity compared to those containing PC as the solvent.

Diffusion of LiCl electrolytes in 3D-nanoporous graphene structures

In this work, we investigate the diffusion of LiCl electrolytes in 3D-nanoporous graphene structures (3D-NGSs) through molecular dynamics simulations. The diffusion coefficients, D, of water, Li+, and Cl− are calculated in 3D-NGSs with different LiCl concentrations, porosities, and surface charge densities under various temperatures. It is found that the diffusion coefficients follow the Arrhenius Equation and power laws for the dependence on the temperature and porosity, respectively. They decrease with increasing salt concentration. At high surface charge densities, the diffusion coefficients decrease with increasing charge density, which, however, plays a minor role in affecting the diffusion coefficients in the range of 0–0.2 C m−2. The mechanisms are investigated through the potential energy distribution in the 3D-NGSs. General scaling laws for the diffusion coefficients of water, Li+, and Cl− are proposed. The results in this work provide useful information for the design of electrodes and various energy systems.