Amorphous Electrodes Research Articles

Enhanced energy density of flexible asymmetric solid state supercapacitor device fabricated with amorphous thin film electrode materials

Supercapacitors have recently received immense interest in scientific community, as a complementary technology to batteries, to meet the various requirements for energy usage in practice. Amorphous MnO2 and CuS thin films are prepared on stainless steel-304 (SS) substrate by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods, respectively. Asymmetric flexible solid state supercapacitor fabricated with configuration of SS/A-MnO2/Polyvinyl acetate (PVA)-Na2SO4/A-CuS/SS delivered an impressive specific energy of 57.4 Wh kg−1 at specific power 317 W kg−1 and excellent cycling stability over 10,000 cycles with capacitive retention of 84%. Moreover, series configuration of two asymmetric devices shows the capability of powering 211 red LEDs for ~150 s after charging for 30 s.

Electrodeposition of MoSx: Tunable Fabrication of Sulfur Equivalent Electrodes for High Capacity or High Power

In this study, amorphous MoSx electrodes were fabricated by a facile one step electrodeposition method as sulfur equivalent cathode structures for lithium based batteries. By modifying the deposition conditions, the physical, chemical, and resulting electrochemical properties of MoSx were manipulated to achieve either higher energy delivery or higher power delivery. MoSx deposited at anodic potential (MoSx-AD) showed a higher initial capacity of 900 mAh g−1 attributed to its higher sulfur content. In contrast, MoSx deposited at cathodic potential (MoSx-CD) exhibited a lower initial capacity of 500 mAh g−1 with improved cycling stability up to 100 cycles and significantly improved rate capability attributed to its higher conductivity and improved Li+ transport properties.

Phytic acid controlled in situ synthesis of amorphous cobalt phosphate/carbon composite as anode materials with a high mass loading for symmetrical supercapacitor: amorphization of the electrode to boost the energy density.

Transition metal phosphate (TMPi)-based composites as anode electrode materials in supercapacitor applications are less reported. Herein, we report a phytic acid (PA)-assisted in situ-formed amorphous cobalt phosphate/carbon (CoPi/C) composite grown on a flexible woven carbon cloth (CC) via a simple one-step carbonization approach. The tunable synthesis of amorphous and crystalline composites is shown by simply controlling the concentration of the cobalt salts. The strategy for high mass loading to 12 mg cm−2 is also shown in this report. Importantly, the resulting amorphous electrode materials exhibit electric double-layer capacitance (EDLC) behavior that works over a wide potential range from −1.4 to +0.5 V in an aqueous solution of potassium hydroxide (2 M KOH) and from −1.5 to +1.5 V in sodium sulfate (1 M Na2SO4). The amorphous electrode as an anode is capable of delivering an areal capacitance up to 2.15 F cm−2 at a current density of 4 mA cm−2 (gravimetric capacitance up to 606.1 F g−1 at 1 Ag−1) and has a retention of 94.2% at 10 000 cycles. The flexible solid-state symmetric device fabricated shows an energy density of approximately 620.0 μW h cm−2 at a power density of 4.7 mW cm−2 (31.1 W h kg−1 at 476.0 W kg−1). This study offers a novel route for the generation of metal phosphate-based anode materials with high capacitance for symmetrical supercapacitor device with high energy density.

Enhanced stability and ultrahigh activity of amorphous ripple nanostructured Ni-doped Fe oxyhydroxide electrode toward synergetic electrocatalytic water splitting.

The development of high-performance catalysts for oxygen-evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals. Here we report, highly efficient, ultra-durable and earth-abundant Ni@Fe-NP electrocatalysts developed by solvothermal method for oxygen evolution reaction (OER). The newly developed oxygen electrode show prolonged stability and high catalytic-activity in line with water oxidation keeping alkaline condition which requires overpotential of only 211 mV at current density of 10 mA cm−2. Collectively, the as-prepared amorphous Ni@Fe-NP rippled nanostructured electrode is the most effective oxygen evolution electrode in alkaline solution. Therefore, this study will offer exciting new avenues for designing self-supported electrode materials towards water splitting and other applications.

Precipitating Metal Nitrate Deposition of Amorphous Metal Oxyhydroxide Electrodes Containing Ni, Fe, and Co for Electrocatalytic Water Oxidation

We report here a facile, one-step precipitating metal nitrate deposition (PMND) method to prepare amorphous metal oxyhydroxide films containing Fe, Co, and Ni as efficient electrocatalysts for wate...

Polyaniline-coated VS4@rGO nanocomposite as high-performance cathode material for magnesium batteries based on Mg2+/Li+ dual ion electrolytes

Magnesium batteries based on Mg2+/Li+ dual ion electrolytes (MLIBs) have attracted increasing attention due to fast Li+ or Mg2+/Li+ insertion kinetics, abundant Mg resources, and high volumetric capacity of dendrite-free Mg anodes. Herein, we report polyaniline (PANI)–coated VS4@reduced graphene oxide (rGO) with nanostructures synthesized via hydrothermal synthesis and subsequent PANI polymerization as the cathode material for MLIBs. The PANI layer serves as a conductive medium to enhance electron transfer and Mg2+/Li+ transportation as well as to mitigate the structure changes of VS4 during the cycling process. Indeed, this material demonstrates enhanced electrochemical performance with a high discharge capacity of 200.7 mAh g−1 after 20 cycles and 91.2% retention after 50 cycles. Mechanism analysis reveals that Li+ insertion into VS4 produced an amorphous VS4 host in the first discharge, which inclined to store Mg2+ rather than Li+ in the subsequent cycles. Our study provides new insights into the development of amorphous electrode materials for magnesium batteries.

Defect-Driven Niobium Oxide Electrode for Lithium-Ion Batteries

The development and innovation of new electrode materials is needed for the next generation of electrochemical energy storage systems (EES). Lithium-ion batteries (LIB) are the leading technology in EES, however, they are plagued with several limitations including safety and stability. Metal oxide electrodes could provide a safer battery while maintaining high reversible capacity. When compared to the commonly used graphite, metal oxides operate at voltages above that of Li plating for safe operation. In addition, nanostructured metal oxides could enhance the performance of the battery by facilitating fast electron and ion transport. Traditionally, intercalation compounds of well-ordered close-packed oxides have been prized because of the general consensus that well-ordered structures having little or no intermixing between Li and transition metal sublattice are required to achieving high capacity with good stability. Consequently, disordered materials have received limited attention and have been less studied. Nevertheless, in recent years evidence has shown that transition metal oxides which have structural defects (e.g., vacancies and interstitials) at cation sites with local disorder have the potential to offer higher capacity and better stability compared to ordered oxides. In this talk, we report our integrated experimental and computational study of a nanostructured amorphous niobium oxide electrode for lithium ion battery. An irreversible phase transformation from amorphous to crystalline phase in niobium oxide electrode is observed during the first discharging process. The newly formed crystalline niobium oxide electrode exhibits high capacity, superb rate capability and good cycle life. The electrochemical charge storage mechanisms of the new electrode will be discussed.

Amorphous Core–Shell Nanoparticles as a Highly Effective and Stable Battery‐Type Electrode for Hybrid Supercapacitors

AbstractHerein, a silver@amorphous nickel–cobalt hydroxide (Ag@NCOH) battery‐type electrode with the morphology of core–shell nanoparticle is successfully fabricated through coordination etching and precipitating route. This electrode exhibits excellent electrochemical performance, including superior specific capacity (≈718.1 C g−1 at 1 A g−1), excellent rate capability (71.9% capacity retention at 30 A g−1), as well as good cycling stability (83.2% capacity retention over 4000 cycles) for hybrid supercapacitors. According to the results of the characterization analysis and systematic electrochemical testing, the Ag nanoparticles in core–shell structure can significantly enhance the conductivity and accelerate the rate of electron transport. Meanwhile, the nanostructures and grain boundaries of amorphous hydroxide materials can effectively improve to expose the electrochemical active sites to electrolyte. Moreover, the hybrid supercapacitor assembled from Ag@NCOH and active carbon (AC) exhibits good performance (energy density of 39.88 W h kg−1 at power density of 375 W kg−1) and superior cycling stability (85.39% capacitance retention over 9000 cycles). This work demonstrates an effective strategy to construct highly effective and stable amorphous electrode materials for hybrid supercapacitors.

Completing the Picture of the Solid Electrolyte Interphase

Although solid electrolyte interphase (SEI) formation is an important factor in battery performance, difficulties in characterizing the SEI mean that it is still not well understood. In this issue of Joule, Nanda and coworkers utilize tip-enhanced Raman spectroscopy to paint a more complete picture of the SEI on silicon electrodes.

Vanadium-based polyoxometalate as electron/ion sponge for lithium-ion storage

Polyoxometalates with multiple redox reactions have been reported as electron/ion sponges for lithium-ion storage applications. Here we introduce a vanadium-based polyoxometalate, Na7H2[PV14O42] (NPV), as an anode material for Lithium-ion batteries (LIBs). NPV exhibits a high reversible capacity up to 687 mA h g−1 at 100 mA g−1 with a good capacity retention of ~80% after 150 cycles. In operando synchrotron X-ray absorption near edge structure reveals the change of the valences of vanadium from V4+ to V1.87+, indicating that it can transfer at least 30 electrons per molecule which leads to high capacity. In operando synchrotron X-ray diffraction confirms the crystal structure of NPV electrode converts to amorphous during charge/discharge processes. Therefore, the charge storage mechanism of NPV could be further proposed that Li ions insert into amorphous NPV electrode continuously and react with [PV14O42]9- molecules, and [PV14O42]9- is like an electron/ion sponge which can store at least 30 electrons.

Structural transformation and embrittlement during lithiation and delithiation cycles in an amorphous silicon electrode

Silicon shows potential as an anode material in lithium ion batteries due to its high specific capacity, yet its considerable volume expansion during lithiation leads to fracture and pulverization. Unfortunately, neither the atomic-level structural evolution, nor the mechanical behavior of the anode during lithiation and delithiation cycles is well understood. Interestingly, the lithiation process of a-Si provides an interesting continuum from open-structured network glass to densely-packed atomic glass, which could be used to obtain useful insights regarding commonalities in glasses. Here atomic level simulation has been used to investigate one cycle of lithiation and delithiation of amorphous silicon electrode, using Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The atomic level structural transformation and damage accumulation of the anode during cycling has been systematically analyzed, as well as their mechanical responses in compact tension tests. There appears to be a ductile-brittle-ductile transition for the amorphous silicon anode during both the lithiation and delithiation cycle. In other words, amorphous silicon is particularly vulnerable at intermediate lithiation. The fracture behavior of lithiated silicon was found to correlate to the Poisson's ratio, due to variations in bond covalency and structural disorder.

"Buried" Surfaces: Membrane-like Coatings for Favorable Electrocatalytic Selectivity

For existing large-scale industrial processes (chlorate process) as well as emerging technologies (photocatalytic water splitting) electrochemical selectivity towards hydrogen evolution is essential to achieve high (energy) efficiencies. Electrode selectivity is widely reported to be achieved in the presence of solution additives such as sodium dichromate (Na2Cr2O7) [1]. In the chlorate process dichromate is known to form a thin membrane-like structure by reductive electrochemical deposition on the cathode. With the growing interest in the electrification of the chemical industry and the general need for clean energy technologies, the development of membrane-coated “buried” electrodes recently received increasing attention [2]. In this presentation, 1) the formation of amorphous oxide electrode coatings from chromate solutions will be described and 2) potential alternative coatings, particularly coatings derived from permanganate and vanadate electrolyte additives, will be introduced [3,4]. It will be shown by different electroanalytical techniques that these amorphous oxide overlayers are selectively permeable to certain electroactive species (Figure 1) and enable efficient hydrogen evolution without significantly altered kinetics.

Amorphous V2O5 Positive Electrode Materials by Precipitation Method in Magnesium Rechargeable Batteries

Amorphous vanadium pentoxide (a-V2O5) was prepared via the precipitation method, for use as a positive-electrode material in magnesium rechargeable batteries (MRBs). Amorphous metal oxides can be good candidates as the host materials for the Mg divalent ion because of many vacancies and huge void spaces. Furthermore, amorphous metal oxides generally do not experience a phase change during cycles. The electrochemical characteristics of the a-V2O5 and c-V2O5 (crystalline vanadium pentoxide) were evaluated and compared. Both a-V2O5 and c-V2O5 can store over 150 mAh/g of the Li+ ion in activated carbon (AC)/V2O5 cells, however, Mg2+ ion cannot be stored in both a-V2O5 and c-V2O5 in the first cycle. But, the specific capacity of a-V2O5 gradually increases up to 180 mAh/g after the 10th cycle, whereas c-V2O5 cannot react continuously. Therefore, the a-V2O5, which has a large specific capacity and high reaction voltage, can be a good candidate as a host material for MRBs because its amorphous structure has the advantage of the multi-valent ion storage.

Amorphous Ni‐Rich Li(Ni1−x−yMnxCoy)O2–Li2SO4 Positive Electrode Materials for Bulk‐Type All‐Oxide Solid‐State Batteries

AbstractAll‐solid‐state batteries attract significant attention owing to their potential to realize an energy storage system with high safety and energy density. In this paper, a mechanochemical synthesis of novel amorphous positive electrode materials of the Ni‐rich LiNi1−x−yMnxCoyO2 (NMC)–Li2SO4 system suitable for oxide‐type all‐solid‐state batteries is reported. Through the mechanochemical treatment with Li2SO4, excellent formabilities of the electrode materials as those of ductile solid electrolytes are obtained. Owing to the deformability of the active material, a good electrode/electrolyte interface is provided simply by pressing at room temperature. In all‐oxide solid‐state cells using 80NMCs·20Li2SO4 (mol%) positive electrode materials, the cell capacity increases with the Ni content in the NMC. The all‐solid‐state cell using the 80NMC811·20Li2SO4 positive electrode active material exhibits a high capacity larger than 250 mAh g−1 in a voltage range of 1.6–4.8 V versus Li at 100 °C. Furthermore, bulk‐type all‐oxide solid‐state batteries (Li4Ti5O12/80NMC532·20Li2SO4 (mol%)) successfully function as secondary batteries with excellent cycle performances.

Structural Transformation and Embrittlement During Lithiation and Delithiation Cycles in an Amorphous Silicon Electrode

Silicon shows potential as an anode material in lithium ion batteries due to its high specific capacity, yet its considerable volume expansion during lithiation leads to fracture and pulverization. Unfortunately, neither the atomic-level structural evolution, nor the mechanical behaviors of the anode during lithiation and delithiation cycles is well understood. Interestingly, the lithiation process of a-Si provides an interesting continuum from open-structured network glass to densely-packed atomic glass, which could be used to obtain useful insights regarding commonalities in glasses. Here atomic level simulation has been used to investigate one cycle of lithiation and delithiation of amorphous silicon electrode, using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The atomic level structural transformation and damage accumulation of the anode during cycling has been systematically analyzed, as well as their mechanical responses in compact tension tests. There appears to be a ductile-brittle-ductile transition for the amorphous silicon anode during both the lithiation and delithiation cycle. In other words, amorphous silicon is particularly vulnerable at intermediate lithiation. The fracture behavior of lithiated silicon was found to correlate to the Poisson’s ratio, due to variations in bond covalency and structural disorder.

On the unsuspected role of multivalent metal ions on the charge storage of a metal oxide electrode in mild aqueous electrolytes.

Insertion mechanisms of multivalent ions in transition metal oxide cathodes are poorly understood and subject to controversy and debate, especially when performed in aqueous electrolytes. To address this issue, we have here investigated the reversible reduction of nanostructured amorphous TiO2 electrodes by spectroelectrochemistry in mild aqueous electrolytes containing either a multivalent metal salt as AlCl3 or a weak organic acid as acetic acid. Our results show that the reversible charge storage in TiO2 is thermodynamically and kinetically indistinguishable when carried out in either an Al3+- or acetic acid-based electrolyte, both leading under similar conditions of pH and concentrations to an almost identical maximal charge storage of ∼115 mA h g-1. These observations are in agreement with a mechanism where the inserting/deinserting cation is the proton and not the multivalent metal cation. Analysis of the data also demonstrates that the proton source is the Brønsted weak acid present in the aqueous electrolyte, i.e. either the acetic acid or the aquo metal ion complex generated from solvation of Al3+ (i.e. [Al(H2O)6]3+). Such a proton-coupled charge storage mechanism is also found to occur with other multivalent metal ions such as Zn2+ and Mn2+, albeit with a lower efficiency than Al3+, an effect we have attributed to the lower acidity of [Zn(H2O)6]2+ and [Mn(H2O)6]2+. These findings are of fundamental importance because they shed new light on previous studies assuming reversible Al3+-insertion into metal oxides, and, more generally, they highlight the unsuspected proton donor role played by multivalent metal cations commonly involved in rechargeable aqueous batteries.

Revealing the atomistic origin of the disorder-enhanced Na-storage performance in NaFePO4 battery cathode

Among the various types of cathode materials for sodium ion batteries, NaFePO4 attracts much attention owing to its high theoretical capacity (155 mA h g−1), low cost, high structural stability, and non-toxicity. Nevertheless, the NaFePO4 with maricite structure, thermodynamically stable phase, has been considered as electrochemically inactive for sodium-ion storage. In this work, we succeeded in tuning the degree of disorder in NaFePO4 cathode material by a mechanochemical route to enhance electrochemical performances of Na-ion batteries. The derived NaFePO4 cathodes containing both amorphous and maricite phases exhibit much improved sodium storage performance with an initial capacity of 115 mA h g−1 at 1 C and an excellent cycling stability of capacity retention of 91.3% after 800 cycles. By X-ray absorption near edge and Raman spectroscopy, we revealed the atom-scale structural origin of the enhanced Na-storage performances of the amorphous NaFePO4 electrode. The transformation of edge-sharing FeO6 octahedra into various FeOn polyhedra upon amorphization was found to be a key to attain the superior performances for Na ion batteries.

Constructing Heterointerface of Metal Atomic Layer and Amorphous Anode Material for High-Capacity and Fast Lithium Storage.

Interfacial engineering plays an important role in tuning the intrinsic property of electrode materials for energy applications such as lithium-ion batteries (LIBs), which however is rarely realized to amorphous electrode materials, despite a set of characteristics of amorphous materials desirable for LIBs. Here, Au atomic cluster layer-interfaced amorphous porous CoSnO3 nanocubes were fabricated by galvanic replacement and employed as a superior LIB anode, showing high reversible capacity (1615 mAh g-1 at 0.2 A g-1), good rate capability (1059 mAh g-1 with a 61.3% capacity retention upon the dramatic current variation from 0.1 to 5 A g-1), and excellent cycling stability. The amorphous nature, interconnected mesopores, and especially the thin Au atomic cluster layer on the surface/pore walls of CoSnO3 nanocubes can not only improve electron transport and ion diffusion in the electrode and electrolyte but also release the volume strain. Most significantly, density functional theory calculations reveal that the CoSnO3∥Au heterointerface can induce the atomic polarization of CoSnO3 and lower Li ion diffusion barriers in CoSnO3 near the heterointerface, endowing it with a significantly enhanced theoretical lithium storage capacity and outstanding rate capability. This study provides a model of a heterointerface for amorphous materials with desired properties for high-performance LIBs and future energy applications.

Flexible and transparent IWO films prepared by plasma arc ion plating for flexible perovskite solar cells

We investigated flexible W-doped In2O3 (IWO) electrodes prepared by arc plasma ion plating (APIP) as a substitute for sputtered amorphous ITO electrodes in flexible perovskite solar cells (FPSCs). In spite of the room temperature ion plating process, the APIP-grown IWO film showed a low sheet resistance of 37.14 Ohm/square, a high optical transmittance of 96.0%, high near IR transmittance, and a small bending radius of 5 mm. In addition, the IWO film shows an atomically smooth surface with a root mean square roughness of 0.83 nm due to the absence of the resputtering effect during the ion plating process. The FPSC with the ion-plated IWO electrode showed comparable performances to a commercial amorphous ITO electrode in an FPSC with an open circuit voltage (0.837 V), short circuit current (18.67 mA/cm2), fill factor (72.54%), and power conversion efficiency (11.33%). Moreover, the microstructure and interfacial structure of the APIP-grown IWO film employed in a FPSC were examined by high-resolution transmission electron microscopy and the sheet resistance of the IWO films was correlated to the FPSC performance.

Amorphous Iron(III)-Borate Nanolattices as Multifunctional Electrodes for Self-Driven Overall Water Splitting and Rechargeable Zinc-Air Battery.

Highly stable and low-cost electrocatalysts with multi-electrocatalytic activities are in high demand for developing advanced energy conversion devices. Herein, a unique trifunctional amorphous iron-borate electrode is developed, which is capable of boosting hydrogen evolution, oxygen evolution, and oxygen reduction reactions simultaneously. The amorphous iron borate can self-assemble into well-defined nanolattices on electrode surface through a facile hydrothermal process, which possess more active sites and charge transfer pathways. As a result, the asymmetry overall water-splitting cell that adopts the amorphous electrodes as anode and cathode can be driven at 1.56 V with the current density of 10 mA cm-2 , which is lowest in state-of-the-art catalysts. Moreover, the water-splitting devices can be powered by a two-series-connected amorphous electrode-based zinc-air battery with high stability and Faradic efficiency (96.3%). The result can offer a potential and promising alternative way to develop metal-borate electrode for multifunctional applications.