Utilization Rate Of Active Materials Research Articles

Hierarchical porous N-doped carbon fibers enable ultrafast electron and ion transport for Zn-ion storage at high mass loadings

Zinc-ion capacitors (ZICs) are a promising and safe energy storage system for portable electronics but usually limited by relatively low areal capacity and energy density. Although increasing the mass loading has been suggested, thick electrode layers and clogged pores unavoidably lead to sluggish electron transport and ion diffusion as well as “dead volume” of active materials. Herein, a millimeter-scale 3D thick-network electrode, composed of closely intertwined hierarchical porous N-doped and free-standing carbon nanofibers (HPNCFs), was fabricated via carbonization of nanoscale zeolitic imidazolate framework (ZIF-8) particles embedded in electrospun polyacrylonitrile (PAN) nanofibers. With fast electron/ion transport, large ion-accessible surface area and high utilization rate of active materials, the mass loading of the HPNCFs electrode can reach 48.67 mg cm−2 with a thickness of 4.46 mm. Moreover, the HPNCFs-based ZICs can yield a superior areal/gravimetric capacity of 4.13 F cm−2 /280 F g−1, superior rate capability up to 193.7 F g−1 even at 100 A g−1, high energy density of 99.6 Wh kg−1, and long-term stability for 40,000 cycles. The straightforward approach can provide an opportunity to prepare efficient thick electrodes that could be applied in electrocatalysis, energy storage/conversion, and other electrochemical energy-related techniques.

Fe3O4 nanoparticles anchored on carbon nanotubes as high-performance anodes for asymmetric supercapacitors

Fe3O4/CNT composites are synthesized with ethylene glycol as solvent by a one-step solvothermal method and used as anode materials for asymmetric supercapacitors (ASC). An appropriate amount of water in ethylene glycol can accelerate the formation of Fe3O4 and reduce the average size of Fe3O4 to around 20 nm. However, spherical Fe3O4 particles larger than 100 nm will form in pure ethylene glycol for long reaction time. The Fe3O4/CNT composite with small Fe3O4 nanoparticles exhibits a high specific surface area, promoted electron transfer ability, as well as a high utilization rate of active materials. The optimized electrode shows a high specific capacity of 689 C g−1 at 1 A g−1, and remains 443 C g−1 at 10 A g−1. The inferior long-term cycling stability is due to the phase transition of Fe3O4 and a reductive effect to form metallic Fe. An ASC using Fe3O4/CNT and NiCoO2/C composites as anode and cathode, respectively, delivers a high energy density of 58.1 Wh kg−1 at a power density of 1007 W kg−1 in a voltage window of 1.67 V and has a capacity retention of 63% after 5000 cycles. The self-discharge behavior of the ASC is also investigated.

Ultrafine manganese hexacyanoferrate with low defects regulated by potassium polyacrylate for high-performance aqueous Zn-ion batteries

Manganese hexacyanoferrate (MnHCF) is an ideal candidate for aqueous Zn-ion batteries (AZIBs) because of their high capacity and high operating voltage. Adding surfactant during the preparation process is an effective way to reduce the [Fe(CN)6] vacancies and water, leading to a stable structure and excellent electrochemical performance. However, the size of MnHCF becomes large (> 100 nm) after adding surfactant, resulting in the sluggish kinetics of Zn-ion transport and low utilization rate of active materials. Herein, ultrafine MnHCF (15 nm) (MnHCF-15) with few vacancies and low water content has been fabricated by introducing a typical surfactant of potassium polyacrylate (PAAK). Moreover, PAA-K can also precisely regulate the size of MnHCF, which exhibit a series of nano-sizes of 15, 50, 80, and 120 nm. The MnHCF-15 cathode exhibited a high capacity of 139.2 mA h g−1 at 0.05 A g−1 with a high operating voltage of 1.75 V. The excellent cycling stability of 92.5 %, 91.9 %, and 84.5 % capacity retention at 0.1, 0.2, and 0.5 A g−1 for 1000 cycles were also achieved because of the ultrafine size and the low defect of MnHCF-15. Ex-situ XRD and XPS were carried out to probe Zn-ion storage mechanism, indicating a reversible electrochemical reaction of the MnHCF-15 cathode. Impressively, the soft-packed AZIBs with high electrochemical performance highly reveal the practical application of the MnHCF-15. The results of this work offer a promising cathode material and lead to a new understanding on the nano-size effect of PBAs in AZIBs.

Flexible electrospun FeCo/carbon hybrid nanofiber films as binder-free anodes for enhanced lithium storage performance

The design of electrodes with excellent mechanical elasticity is the significant to developing flexible electronic devices with mechanical endurance and outstanding lithium storage properties. Herein, the flexible FeCo/carbon hybrid nanofiber membranes (named as FeCo@CNFM) were successfully prepared via electrospinning and subsequent carbonization process. From the macroscopic perspective, the FeCo@CNFM can bend at a large angle without any destruction, and be directly used as working electrode of lithium ions batteries (LIBs) without any expensive additives, demonstrating its extraordinary mechanical flexibility. From the microscopic perspective, the homogeneously dispersed fine FeCo nanoparticles and the three-dimensional (3D) interconnected transport network constructed of carbon nanofibers significantly shorten the lithium-ion transfer distance, eliminate the volume fluctuation during lithiation/delithiation process, enhance the utilization rate of active materials, and promote the electrical conductivity of the composite electrode, thus leading to remarkably improved electrochemical properties. As a consequence, the optimized FeCo@CNFM manifests a superior discharge capacity of 584.9 mA h g−1 at 100 mA g−1 after 100 cycles with long cycling stability and good rate capability of 227.1 mA h g−1 even at a large current rate of 2 A g−1, making it a promising flexible self-supporting anode for LIBs.

Self-Supporting Multicomponent Hierarchical Network Aerogel as Sulfur Anchoring-Catalytic Medium for Highly Stable Lithium-Sulfur Battery.

The low utilization rate of active materials, shuttle effect of lithium polysulfides (LiPSs), and slow reaction kinetics lead to the extremely low efficiency and poor high current cycle stability of lithium sulfur batteries (Li-S batteries). In this paper, a self-supporting multicomponent hierarchical network aerogel is proposed as the modified cathode (S/GO@MX@VS4 ). It consists of graphene (GO) and MXene nanosheets (MX) loaded with VS4 nanoparticles. The experimental results and first-principles calculations show that the GO@MX@VS4 aerogel has strong adsorption and reversible conversion effects on LiPSs. It can not only inhibit the shuttle effect and improve the utilization rate of active substances by keeping the chain crystal structure of VS4 , but also promote the reversibility and kinetics of the reaction by accelerating the liquid-solid transformation in the reduction process and the decomposition of insoluble Li2 S in the oxidation process. The GO@MX@VS4 aerogel modified cathode with a multicomponent synergy exhibits the capacity ratios (Q1 /Q2 ) at different discharge stages is close to the theoretical value (1:2.8), and the capacity decay per cycle is 0.019% in 1200 cycles at 5C. Also, a high areal capacity of 6.90 mAh cm-2 is provided even at high sulfur loading (7.39mg cm-2 ) and low electrolyte/sulfur ratio (E/S, 8.0µL mg-1 ).

Excimer ultraviolet-irradiated graphene separator for suppressing polysulfide shuttling in Li–S batteries

Lithium–sulfur (Li–S) batteries are expected to become efficient new-generation energy storage systems owing to their properties such as high theoretical specific capacity (1675 mAh g−1) and high energy density (2600 Wh kg−1). However, some factors restrict their rapid development; for example, the dissolution and migration of polysulfides during the charge and discharge process, extremely poor conductivity of sulfur, and increase in volume. A glass fiber separator with graphene was loaded on a surface modified by excimer ultraviolet light (EUV/graphene separator) as the separator for Li–S batteries. The modified separator was irradiated by excimer ultraviolet light with graphene powder loaded on a glass fiber via vacuum filtration; this can effectively block polysulfide diffusion and improve the utilization rate of active materials when assembled into a Li–S battery. The first discharge specific capacity for this separator was as high as 1164 mAh g−1 at 0.2 C; after 300 cycles, the specific capacity was maintained at 640.5 mAh g−1. This modified separator guarantees the efficient migration of lithium ions and effectively inhibits the shuttle effect of Li–S batteries.

Review of Cathode in Advanced Li−S Batteries: The Effect of Doping Atoms at Micro Levels

AbstractIn recent years, the atom‐doping strategy has attracted extensive attention in lithium‐sulfur batteries. The reasonable structure design and introduction of doping atoms into sulfur cathode materials not only improve the utilization rate of active materials but also catalyze the redox kinetics of polysulfides, which greatly improves the electrochemical performance of the lithium‐sulfur batteries. However, the understanding of the functional mechanism and conversion mechanism of the doping atoms at micro levels is still limited. Hence, it is very crucial to explore the influence of doping atoms on the electronic arrangement and electrochemical active sites. Herein, the development of atomic doping in lithium‐sulfur batteries is reviewed, and the structure‐activity relationship between doped atoms and the adsorption of lithium polysulfide is analyzed. Furthermore, the catalytic mechanisms of catalytic materials were unmasked from microscopic perspectives, namely ion transport, surface electronic structure, energy band structure and state density.

High utilization rate thermal batteries using PbCl2 as a cathode material

In view of the shortcomings of low utilization rate of disulfide cathode for thermal battery, chloride has been developed as a candidate material for thermal battery cathode. In this case, PbCl2 was tried to be used as a cathode material for thermal batteries and tested the electrical properties of single battery. The discharge specific capacity can reach 168 mAh/g at 450 °C and 0.5 C current, the voltage plateau reaches 1.8 V, and the active material utilization rate is as high as 87.5% when the cut-off voltage is 0.5 V. The only discharge platform and high utilization rate enable PbCl2 to be used as the active material for thermal batteries, which also provides a new direction for the chloride cathode active material for thermal batteries.

Electrospun FeCo nanoparticles encapsulated in N-doped carbon nanofibers as self-supporting flexible anodes for lithium-ion batteries

This work reports a flexible, self-supporting anode, as a novel electrode material to improve the energy density of lithium-ion batteries (LIBs). In this work, FeCo nanoparticles uniformly encapsulated in one-dimensional N-doped carbon nanofibers (denoted as FeCo@NCNFs) were synthesized by electrospinning and subsequent thermal treatment. The as-prepared FeCo@NCNFs films with high electrical conductivity and good flexibility can be directly used as LIBs anodes without the addition of any conductive agents and binders. The lithium storage performance of FeCo@NCNFs is far superior to that of pure NCNFs. The impact of the carbonization temperature on the structure and electrochemical properties of FeCo@NCNFs was also investigated. Results show that FeCo@NCNFs obtained at 600 °C exhibits the optimal electrochemical performance with a relatively high reversible capacity, i.e., 566.5 mA h g−1 at 100 mA h g−1 after 100 cycles. The enhanced electrochemical properties can be mainly attributed to the synergy between 3D conductive NCNFs network and small FeCo nanoparticles, which can effectively improve the utilization rate of active materials, facilitate the transport of the electrons and lithium ions, and promote the charge-transport kinetics. Moreover, the homogeneous dispersion of FeCo nanoparticles in the NCNFs can also greatly buffer the volume change and improve the structural stability of the electrodes during the charge-discharge cycling.

Investigation the electrochemical properties of LiCl-LiBr-LiF-doped Li7La3Zr2O12 electrolyte for lithium thermal batteries

Li7La3Zr2O12 (LLZO) has been considered as one of the most promising electrolytes for lithium batteries due to its high safety and wide electrochemical window. However, few reports were observed for the application of LLZO on lithium thermal batteries. In this paper, LLZO was studied as the electrolyte of lithium thermal battery. To further improve the performance of LLZO, LLZO-LiCl-LiBr-LiF composite electrolyte was designed by mechanical mixing LiCl-LiBr-LiF eutectic salt with LLZO. The doping content of LiCl-LiBr-LiF was also investigated, and the results showed that the optimize content was 15% (in weight) LiCl-LiBr-LiF. For instance, the specific capacity of the battery using LLZO-(LiCl-LiBr-LiF)x (x = 15%) as electrolyte was 224.6 mAh g−1, the active material utilization rate was 85.08%, and the service life of lithium thermal battery can be extended to 25 min under 80 mA cm−2 at 550 °C. The superior electrochemical properties of LLZO-(LiCl-LiBr-LiF)x (x = 15%) were ascribed to the larger ionic conductivity (2.802 × 10−2 S cm−1 at 550 °C). Our study not only successfully improves the electrochemical properties of LLZO by compositing with LiCl-LiBr-LiF electrolyte but also paves the way for the practical application of LLZO-LiCl-LiBr-LiF composite in the lithium thermal batteries.

Effects of nano-SiO2 doped PbO2 as the positive electrode on the performance of lead-carbon hybrid capacitor

The PbO2 electrodes of lead-acid batteries are normally applied as the positive electrodes in lead-carbon hybrid capacitors. However, the effective utilization rate of active materials in the electrodes is only about 12.5%, leading to a low energy density of lead-carbon hybrid capacitors. In this paper, a nano-SiO2 doped PbO2 electrode was prepared by the co-electrodeposition method. The energy density of the lead-carbon hybrid capacitor using a nano-SiO2/PbO2 electrode can reach 61 Wh kg−1 at 3 A g−1. The results show that the inert nano-SiO2 can establish electrolyte diffusion channels in the positive electrode, and thus improve the effective utilization rate of active materials. This work provides a new idea for the design and development of the positive materials for high-performance lead-carbon hybrid capacitors.

Design and synthesis of 3D hierarchical NiMoS4@CuCo2S4 array electrode with excellent electrochemical performance

Large capacitance energy storage materials have a great application prospect due to the development of portable devices. An electrochemical deposition method was used to combine amorphous CuCo2S4 with NiMoS4, which was prepared by a two-step hydrothermal method. The resulting grass-like nanowire array structure greatly promotes the utilization rate of active materials. By the addition of two variable valence metal ions, there is an increase in electrolyte touchable active sites and a decrease in the impedance of the electrode materials. Compared with bare NiMoS4, the binder-free composite electrode has a significantly better capacitance characteristic. In particular, the NiMoS4@CuCo2S4−8 has excellent capacity performance with a specific capacitance of 13.14 F cm−2 at the current density of 5 mA cm−2. The electrode shows 73% capacitance retention after 2000 charge-discharge cycles. It is shown that the combined effect of the nanowires and the several variable valence metal ions is effective to increase the specific capacitance of bimetallic sulfides.

Pre-embedding Lithium to Build a Composite SnO2@Li/MWCNTs Anode

Lithium ions were inserted into the electrodes of tin oxide to eliminate the first irreversible capacity of the Li-SnO2 batteries. The stabilizing SEI film was obtained from pre-embedding lithium. Thereby, first irreversible capacity of the Li-SnO2 batteries is prevented with significantly increasing the specific capacity and reducing the damage. As a result, the SnO2@Li/MWCNTs electrodes exhibited outstanding electrochemical performance, first discharge specific capacity reached 1700.15 mAh g−1, and the utilization rate of active materials reached as high as 95.89% at 100 mAh g−1. After 100 cycles, the specific discharge capacity remained greater than 499.94 mAh g−1, with a coulombic efficiency of 99.77%.

CNT network crosslinked by metal Co2+ for stabilizing SnO2 anodes

Porous carbon materials are considered potential replacements for metal carriers in Li–SnO2 batteries. Here, a 3D hierarchical porous carbon nanotube (CNT) scaffold was used as a collector to host SnO2. The novel collector comprised Co2+-doped porous carbon (PC) slices and a CNT network. The new Co–PC/CNT electrode demonstrated a high loading capacity of SnO2, accommodated the volume expansion of SnO2, and prevented its aggregation. Co played an important role in improving the initial discharge capacity and coulombic efficiency of the electrode. The SnO2–Co–PC/CNT electrodes exhibited outstanding electrochemical performance. The first-discharge specific capacity reached 2067 mAh·g−1, and the utilization rate of active materials reached 82.92% at a current density of 100 mAh·g−1. After 100 cycles, the specific discharge capacity remained greater than 698 mAh·g−1, with a coulombic efficiency of 99.53%.

α-Ni(OH)2/NiS1.97 heterojunction composites with excellent ion and electron transport properties for advanced supercapacitors.

It is recognized that an effective strategy to promote the industrialization of supercapacitors is to enhance the ion and electronic conductivities of electrode materials. In this work, it is demonstrated that the NO/NS-8 heterojunction material obtained via an epitaxial growth method based on ion exchange can be used as an outstanding electrode material for supercapacitors. The construction of heterojunctions between α-Ni(OH)2 and NiS1.97 allows the components to provide each other with ion or electron transport paths and endows NO/NS-8 with excellent ion and electron transport properties; this leads to a high utilization rate of active materials and an unprecedented high specific capacitance (up to 2375.8 F g-1 at 1 mV s-1 in a three-electrode system). Using the as-prepared NO/NS-8 heterojunction material as an electroactive material, an asymmetric supercapacitor with long cycle life (62.8% capacitance retention after 10 000 cycles at a current density of 5 A g-1) and high energy and power densities (128.4 W h kg-1 at a power density of 402.9 W kg-1 and 63.8 W h kg-1 at 7662.7 W kg-1) is finally demonstrated. This work provides a novel strategy for developing unique heterojunction materials for energy storage.

Development of high-utilization honeycomb-like α-Ni(OH)2 for asymmetric supercapacitors with excellent capacitance.

The low utilization rate of active materials has been a critical obstacle for the industrialization of ultracapacitors. In this study, a thin layer of cross-structured ultrathin α-Ni(OH)2 nanosheets was successfully grown in situ on the surface of a nickel foam as a high-conductivity framework by a vibratory water bath route under a low temperature (80 °C) and mild conditions. Combining the ultrathin α-Ni(OH)2 nanosheets and ultrashort electron transport, the strategy of a perfect intercalation structure of α-Ni(OH)2 and a thin layer of active material on a continuous conductive framework resulted in a high utilization rate of active material, which further achieved high specific capacitance of 213.55 F g−1 at 1 A g−1 in a two-electrode system and high capacitance retention from three to two electrode system (753.79 F g−1 at 1 A g−1 in the three-electrode system). Meanwhile, the device also achieved high energy density of 74.94 W h kg−1 at power density of 197.4 W kg−1 and still retained 24.87 W h kg−1 at power density of 3642 W kg−1.

Electrochemical Charge-Discharge Properties of Co-S/x Wt.% AB5 Composite Materials in Nickel-Based Batteries

The Co-S/x wt.% AB5 (x=0, 10, 20, 30) composite materials were prepared by simply mixing Co-S material fabricated by hydrothermal method and AB5 alloy. The structure and morphology of the composite materials were characterized by XRD and SEM, respectively. The electrochemical properties of the composite electrodes were studied by the galvanostatic charge, discharge test and electrochemical impedance spectroscopy. The results showed that the Co-S/20 wt.% AB5 composite electrode showed the highest discharge capacity and the best cycling stability. The existence of the AB5 alloy improved the electrochemical activity of composite electrodes, reduced the electrochemical polarization resistances and promoted the electrochemical conversion reaction between Co and Co(OH)2. In order to improve the utilization rate of active materials, 0.01 mol/L Na2S2O3 was added into the electrolyte. The electrochemical properties of the composite electrode were significantly enhanced. After fifty cycles, the discharge capacity of the composite electrode increased from 407 to 481.7 mAh/g and the capacity retention increased from 79.7% to 91.2%.

MnFe2O4@C Nanofibers as High-Performance Anode for Sodium-Ion Batteries.

MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g(-1) at 10000 mA g(-1) in comparison of 504 mA h g(-1) at 100 mA g(-1)) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na(+) + 8e(-) → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na(+) + 8e(-)). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na(+) + 8e(-) ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than that of Fe2O3/Fe. Furthermore, a soft package sodium-ion full battery with MFO@C anode and Na3V2(PO4)2F3/C cathode was assembled, delivering a stable capacity of ∼400 mA h g(-1) for MFO@C (with 100 cycles at 500 mA g(-1)) and a promising energy density of 77.8 Wh kg(-1) for the whole battery. This is owing to the distinctive structure of very-fine MnFe2O4 nanodots embedded in porous N-doped carbon nanofibers, which effectively improves the utilization rate of active materials, facilitates the transportation of electrons and Na(+) ions, and prevents the particle pulverization/agglomeration upon prolonged cycling.

Electrochemical properties of Co-S/x wt.% AB5 composite materials

The Co-S/x wt.% AB5 (x=0, 10, 20, 30) composite materials were prepared by simply mixing Co-S material fabricated by hydrothermal method and AB5 alloy. The structure and morphology of the composite materials were characterized by XRD and SEM, respectively. The electrochemical properties of the composite electrodes were studied by the galvanostatic charge, discharge test and electrochemical impedance spectroscopy. The results showed that the Co-S/20 wt.% AB5 composite electrode showed the highest discharge capacity and the best cycling stability. The existence of the AB5 alloy improved the electrochemical activity of composite electrodes, reduced the electrochemical polarization resistances and promoted the electrochemical conversion reaction between Co and Co(OH)2. In order to improve the utilization rate of active materials, 0.01 mol/L Na2S2O3 was added into the electrolyte. The electrochemical properties of the composite electrode were significantly enhanced. After fifty cycles, the discharge capacity of the composite electrode increased from 407 to 481.7 mAh/g and the capacity retention increased from 79.7% to 91.2%.

Study on the Performances of Nickel Hydroxide Coated with Ytterbium Hydroxide at High-Temperature

Abstract The surface of nickel hydroxide [Ni(OH)2] coated with ytterbium hydroxide [Yb(OH)3] and cobalt hydroxide [Co(OH)2] were studied and characterized by XRD, XPS, SEM and constant current recharge technology. The results show that the structure of β-Ni(OH)2 is hexagonal, Co exists mainly in the form of Co2+ with a small amount of Co3+, and the atomic ratio of Co and Ni on the sample surface is more than 8:1. The samples coated of 2 wt% Yb(OH)3 show the maximum discharge capacity and active material utilization rate at 65 °C (0.2, 1, 3 C). After 30 charge/discharge cycles, the discharge cycling stability and the discharge capacity of Ni(OH)2 coated with different contents of Yb (OH)3 are enhanced with increasing of content of Yb(OH)3 under different charge/discharge rates at 65 °C.