Amorphous Electrodes Research Articles

RETRACTED - High discharge capacities of Ti-based quasicrystal electrodes synthesized by mechanical alloying

ABSTRACTTi-based quasicrystals are well known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. This fact is due to that TiZrNi contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemical affinity with hydrogen. TiZrNi quasicrystal absorbs hydrogen up to host metal ratio (H/M) value near to 2.0. The disadvantage is due to the low equilibrium pressure. To solve this problem, we substituted Ti with a small amount of vanadium (V), with the nominal composition Ti45−x VxZr38Ni17 (x = 5, 10, 15) and synthesized by mechanical alloying. The subsequent annealing in vacuum conditions converted the amorphous into an icosahedral quasicrystal (I-phase) with face-centered cubic (FCC) Ti2Ni-type crystal. As the results, we investigated the discharge capacity for both amorphous and quasicrystal electrodes using three electrodes system (working, reference and counter electrodes) at room temperature. The highest discharge capacities obtained were 81.45 mAh/g recorded for amorphous electrode and 318.4 mAh/g for quasicrystal whose compositions is Ti35V10Zr38Ni17 at discharge current density of 15 mA/g. X-ray diffraction measurement was performed to provide the structural information on materials before and after hydrogenation. Microstructures of the materials were studied using an electron scanning microscope and the chemical compositions were confirmed using an EDX-analysis.

(Invited) The Crucial Role of Nano-Sized Porosity in the Lithiation and Stability of Methylated Amorphous Si Electrodes for Li-Ion Batteries

Silicon electrodes are attracting for lithium-ion batteries but their use is impeded by their poor mechanical stability upon operation (huge volume variation takes place upon electrochemical Li insertion in and extraction from the material) and a poorly-controlled growth of surface layers resulting from the electrolyte decomposition products (the so-called solid-electrolyte interphase, SEI). A thin layer of methylated amorphous silicon a-Si(1-x)(CH3) x :H has a much better resistance to electrochemical lithiation/delithiation cycles than amorphous silicon a-Si:H [1]. Methylated amorphous silicon is a carbon-silicon alloy, deposited using PECVD, in which carbon is incorporated in the bulk material under the form of methyl groups CH3 only. We have studied the lithiation processes in the material for various methyl contents x ranging from 0 (a-Si:H) to 0.12. The lithiation process has been investigated using operando infrared spectroscopy in geometry of attenuated total reflection (ATR) where the active thin layer (30 nm) is directly deposited at the surface of the ATR prism. For all the investigated values of the methyl content x in the material, it was observed that the first lithiation proceeds according to a two-phase mechanism [2]: a (highl²y) lithiated phase with a well-defined Li content z (Li z Si phase) progressively invades the active-material film; if lithiation is performed in galvanostatic mode, this regime corresponds to the observation of a potential plateau. When lithiation is pursued beyond the potential plateau, a single-phase behavior is observed: the Li concentration in the active film becomes uniform and increases as long as the lithiation current is maintained. Delithiation and subsequent lithiation/delithiation cycles proceed homogeneously according to this single-phase behavior. When the electrode is thicker (200 nm), extensive electrochemical cycling results in the cracking of the film. The appearance of the crack network can be followed by operando optical microscopy. When the active film is deposited on a reflecting substrate such as stainless steel, the lithiation can also be followed using the same technique by monitoring of interference colors, since the lithiation results in a thickening of the film and in a change of its refractive index. The quantitative analysis of the two-phase regime of the first lithiation shows that the Li content z in the invading phase depends in a non-trivial way upon the methyl content x of the material: z first decreases upon increasing x, then for values of x larger than 0.05, z increases when increasing x. This behavior can be rationalized in the framework of a model describing the first lithiation of a-Si(1-x)(CH3) x :H. Noteworthy, the regime in which z increases upon increasing x can be ascribed to the existence of a methyl-induced porosity of the material at the nanometric scale. Moreover, the careful analysis of color patterns during lithiation demonstrates that the locations at which the lithiation occurs is not homogeneous at the very beginning of the second cycle: color change can be identified at the locations where future cracks will appear (at the end of the second delithiation of the electrode or later). Possible implications regarding the optimization of the material for its use as electrodes in Li-ion batteries will be discussed.

Amorphous Molybdenum Oxysulfide As a Highly-Reversible Anode Material for Na-Ion Batteries

Rechargeable Na-ion batteries (NIBs) have attracted great attention as a promising alternative for lithium-ion batteries (LIBs) due to the earth-abundant and cheap Na resource. In particular, NIBs can be applied for large-scale energy storage and conversion for renewable energy sources such as solar and wind energies. However, the larger radius of Na+ than that of Li+ results in more sluggish diffusion kinetics and more serious damage to the structure of the electrode materials, which cause low capacity, poor rate capability, and cyclic stability. These disadvantages prevent NIBs from practical application, and therefore, it is crucial to search for suitable Na+ storage materials with high performance. Recently, conversion reaction based electrode materials such as transition metal (TM) oxide, sulfide, and phosphide, which have mostly been studied as high-capacity electrodes for LIBs, have been investigated for possible high-capacity NIBs anodes. Similar to conversion reaction with Li, all possible valance states of transition metal (TM) in the materials can be utilized, enabling more than one electron redox reaction per TM, which leads to a generally high specific capacity. However, intrinsic poor conductivity which causes large hysteresis and low reversibility and huge volume change during sodiation/desodiation which deteriorate cycling stability plague many conversion reactions. Over the past decade, nanostructured materials have been widely used to solve these problems of conversion reaction based electrodes by shortening both electronic and ionic pathway and relieving stress during sodiation/desodiation. However, fabricating nanostructured materials usually involves multiple complicated steps, and large surface area of the nanostructure accelerates electrolyte decomposition which induces large irreversible capacity and contact loss between the electrode material and current collector upon repeated cycling. Nowadays, there have been several reports showing that the intrinsically isotropic nature in amorphous materials, which can mitigate the large volume changes associated with charge/discharge process, greatly improves the cycling stability of rechargeable batteries. In addition, amorphous materials commonly show faster reaction kinetics, better reversibility and narrower voltage hysteresis than crystalline materials. However, there have been neither sufficient explanations nor experimental evidences explaining the origin of the high reversibility and cycling stability of the amorphous electrode. Herein, we propose to design a binder- and conductive agent-free amorphous MoOxSy anode for Na-ion batteries using an ultra-simple and facile electrodeposition process. As well as electrochemical performance measurements, we investigated the structure and phase evolution change of the a-MoOxSy during first sodiation and desodiation to better understand the mechanisms underlying the conversion process and the electrochemical behavior. X-ray absorption fine structure (XAFS) measurements, sensitive to short-range order, were used to track the structure and phase evolution of the electrodes during the conversion process. In addition, using TEM analysis, it was clearly proposed that the microscopic mechanisms involved in the reaction of conversion-reaction based electrode, such as the nucleation and evolution of the metal phases and their phase distribution on the nanoscale, have a great impact on the electrochemical performances of the electrodes.

One-pot hydrothermal synthesis of amorphous FeOOH on Ni foam for high performance supercapacitors

In this work, we developed a facile method to prepare FeOOH directly deposited on the Ni foam through one-pot hydrothermal route. The as-prepared FeOOH/Ni foams (FN) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). Electrochemical performances of the as-prepared FN as electrodes were also evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectrometry (EIS) in 1 M KOH aqueous solution. The results indicate that the flocculent amorphous FeOOH flakes homogeneously grown on the surface of Ni foams construct a three-dimensional (3D) porous structure, which not only provides easy penetration of liquid electrolyte, facilitating fast electron transfer and ion diffusion, but also alleviates the volume change of FN electrodes during the charge-discharge process. The optimized FN electrode exhibits a high specific capacitance of 1300 F/g at a current density of 2 A/g, and excellent capacitance retention of 91% after 2000 cycle tests at a current density of 4 A/g. This work would open an avenue for designing high-performance amorphous electrode materials for supercapacitors.

Structural and Electrochemical Properties of RF Sputter Deposited LiCuPO4 Thin Film Cathodes for Li-Ion Microbatteries

To date, the finding of novel cathode materials for Li-ion microbatteries with the superior performances in terms of safety, cycle life, power and energy densities is still a challenge in order to develop small-scale electrical power sources for modern microelectronic devices 1. Recently, electrodes composed of Cu have been investigated as cathode materials for Li-ion batteries such as LiCuPO4 (LCP) 2, Cu3(PO4)2 3, Li3-xCuxPO4 4 , CuF2 5 etc. Besides low cost and environmentally benign, they could deliver a high theoretical gravimetric capacity due to its ability to intercalate more than one Li ion per formula unit 6. In this work, we report the remarkable electrochemical properties of LiCuPO4 thin-film deposited by radio frequency (r.f.) sputtering without heating treatments as cathode material. Fig. 1a shows the XRD patterns of the initial target, crystalline LCP and as-deposited LCP. The initial target and the slurry obtained from a crystalline powder show the same peaks corresponding to well-crystallized LCP phases. However, after deposition at room temperature, the XRD pattern of the as-deposited LCP thin-film has no visible diffraction peak, indicating that the film is amorphous. Fig. 1b shows the SEM images of the as-deposited LCP thin-films on Si substrate. Fig. 1. XRD patterns of the initial target, crystalline LCP and as-deposited LCP a). Corresponding SEM images of as-deposited LCP film from the top view b) and cross-sectional view (inset in figure 1b). Fig. 2 shows the cycle performance of amorphous LCP film at different kinetics. The capacity fading observed for the initial cycles can be attributed to the loss of the active material. Indeed, dissolution of Cu into electrolyte is supposed to form intermediate Cu+ compound leading to the increasingly ineffective reconversion process during recharging 7. The battery delivers a stable capacity of 70 mAh.g-1 (22 μAh.cm-2) at C/10. The capacity can be recovered after cycling at fast C-rate over 160 cycles, revealing that the reversibility of the conversion reactions could be improved with thin-films by sputtering. During this work, the electrochemical performance of both amorphous LCP thin-film and crystalline LCP composite electrode will be discussed. Fig. 2. Discharge capacity of the amorphous LCP film at multi C-rates References Golodnitsky, D.; Yufit, V.; Nathan, M.; Shechtman, I.; Ripenbein, T.; Strauss, E.; Menkin, S.; Peled, E. Advanced materials for the 3D microbattery. J. Power Sources. 2006, 153, 281–287.Amine, K. Active material for lithium batteries. 2001. US6319632 B1.Zhong, G.; Bai, J.; Duchesne, P.N.; McDonald, M.J.; Li, Q.; Hou, X.; Tang, J.A.; Wang, Y.; Zhao, W.; Gong, Z.; Zhang, P.; Fu, R.; Yang, Y. Copper Phosphate as a Cathode Material for Rechargeable Li Batteries and Its Electrochemical Reaction Mechanism. Chem. Mater. 2015, 27, 5736–5744.Snyder, K.; Raguž, B.; Hoffbauer, W.; Glaum, R.; Ehrenberg, H.; Herklotz, M. Lithium Copper(I) Orthophosphates Li3–xCuxPO4: Synthesis, Crystal Structures, and Electrochemical Properties, Z. Für Anorg. Allg. Chem. 2014, 640, 944–951.Wang, F. ; Robert, R. ; Chernova, N.A.; Pereira, N. ; Omenya, F.; Badway, F. ; Hua, X. ; Ruotolo, M. , Zhang, R. ; Wu, L. ; Volkov, V.; Su, D.; Key, B.; Whittingham, M.S.; Grey, C.P. ; Amatucci, G.G. ; Zhu, Y. ; Graetz, J. Conversion Reaction Mechanisms in Lithium Ion Batteries: Study of the Binary Metal Fluoride Electrodes. J. Am. Chem. Soc. 2011, 133, 18828–18836.Ruther, R.E.; Zhou, H. ; Dhital, C.; Saravanan, K.; Kercher, A.K.; Chen, G. ; Huq, A. ; Delnick, F.M. ; Nanda, J. Synthesis, Structure, and Electrochemical Performance of High Capacity Li2Cu0.5Ni0.5O2 Cathodes. Chem. Mater. 2015, 27, 6746–6754.Wang, F.; Kim, S.-W. ; Seo, D.-H.; Kang, K.; Wang, L.; Su, D. ; Vajo, J.J. ; Wang, J. ; Graetz, J. Ternary metal fluorides as high-energy cathodes with low cycling hysteresis. Nat. Commun. 2015, 6, ncomms7668. Figure 1

Internal Photoemission Spectroscopy Measurements of the Energy Barrier Heights between ALD Dielectrics and Ta-Based Amorphous Metals

High speed metal/insulator/metal (MIM) diodes show promise for rectenna based energy harvesting of IR radiation, for IR sensing, and as building blocks for beyond CMOS hot-electron (MIMIM) transistors. Operation of these devices is ideally based on Fowler-Nordheim tunneling, which is exponentially dependent both on electric field and the height of the energy barriers between the metal electrodes and the insulator. Smooth interfaces are thus necessary to control electric fields. The amorphous metal ZrCuAlNi (ZCAN) has been shown to function well as an ultra-smooth bottom electrode for MIM devices,1,2 but suffers from an interfacial oxide layer and thermal instability above ~300 °C. Recently, Ta based amorphous metals such as TaWSi and TaNiSi have been shown to have larger work functions and stability approaching 900 °C and above.3 Precise knowledge of metal/insulator barrier heights is critical for predicting, understanding, and optimizing MIM diode device operation. Although the Schottky-Mott model may be used to predict ideal barrier heights (φBn = ΦM - χi) from the metal vacuum work function (ΦM) and insulator electron affinity (χi), actual barrier heights depend strongly on deposition method and interfacial properties and often deviate substantially. Internal photoemission (IPE) spectroscopy may be used to directly measure barrier heights at buried interfaces. To date, there have been few reports of IPE measurements of MIM structures and none on these amorphous metals. In this work, IPE is utilized to measure the metal/insulator barrier heights in MIM stacks with Ta-based amorphous metal bottom electrodes with TaN as a reference. Results are compared with current-voltage measurements. TaWSi and TaNiSi bottom electrodes were sputtered onto 100 nm of thermally grown SiO2 on silicon followed by deposition of various high-k insulators via atomic layer deposition. Al and Au dots were evaporated through a shadow mask to serve as semitransparent (~10 nm thick) top gates. For IPE, current was monitored under a fixed applied field while photon energy was swept from 2 to 5 eV. A range of negative and positive applied fields were used to characterize both bottom and top interfaces. Barrier heights will be reported for all electrode/insulator combinations. Schottky plots of bias dependent barrier heights vs. square root of electric field for Al2O3 are shown in Fig. 1 for (a) positive bias (Au interface) and (b) negative bias (TaXN interface). A number of conclusions may be drawn from the results of this measurement array. First, metal/Al2O3 barrier heights are qualitatively consistent with the expected TaXN metal work function as determined as a weighted average of the constituent metals. Second, Au/insulator barrier heights are not affected by the bottom electrode. Third, the asymmetry in the current-voltage response (I(-V)/I(V)) is qualitatively consistent with the IPE determined barrier heights whereas ideal theory predictions are not always. TaWSi and TaNiSi electrodes showed consistently higher barrier heights than ZCAN electrodes and comparable performance to high-quality TaN, indicating promise as a thermally stable bottom electrode for MIM tunnel diodes. Support from NSF Center for Sustainable Materials Chemistry, CHE-1606982. 1 N. Alimardani, S.W. King, B.L. French, C. Tan, B.P. Lampert, and J.F. Conley Jr., J. Appl. Phys. 116, 24508 (2014). 2 N. Alimardani, E.W. Cowell, J.F. Wager, J.F. Conley Jr., D.R. Evans, M. Chin, S.J. Kilpatrick, and M. Dubey, J. Vac. Sci. Technol. A 30, 01A113 (2012). 3 J.M. McGlone, K.R. Olsen, W.F. Stickle, J.E. Abbott, R.A. Pugliese, G.S. Long, D.A. Keszler, and J.F. Wager, MRS Commun. 7, 715 (2017). Figure 1

Operando Nanoindentation: A Perfect Platform to Measure the Mechanical Properties of Electrodes during Electrochemical Reactions

We present an experimental platform of operando nanoindentation that probes the dynamic mechanical behaviors of electrodes during real-time electrochemical reactions. The setup consists of a nanoindenter, an electrochemical station, and a custom fluid cell integrated in an inert environment. We evaluate the influence of the argon atmosphere, electrolyte solution, structural degradation and volumetric change of electrodes upon Li reactions, as well as the surface layer and substrate effects by control experiments. Results inform on the system limitations and capabilities, and provide guidelines on the best experimental practices. Furthermore, we present a thorough investigation of the elastic-viscoplastic properties of amorphous Si electrodes, during cell operation at different C-rates and at open circuit. Pure Li metal is characterized separately. We measure the continuous evolution of the elastic modulus, hardness, and creep stress exponent of lithiated Si and compare the results with prior reports. Operando indentation will provide a perfect platform to understand the fundamental coupling between mechanics and electrochemistry in energy materials.

Amorphous nickel oxide and crystalline manganese oxide nanocomposite electrode for transparent and flexible supercapacitor

Among numerous active electrode materials, transition metal oxides are promising electrode materials in supercapacitors. Here, we fabricated amorphous nickel oxide and crystalline manganese oxide nanocomposite positive electrode for transparent and flexible supercapacitor. The nanocomposite was prepared via a two-step method. First, the amorphous nickel oxide film was prepared using a room-temperature chemical solution deposition and photochemical method. UV light irradiation causes condensation and densification of nickel oxide film by photochemical activation at room temperature. Second, the crystalline manganese oxide was prepared by chemical bath deposition method. The synergistic effect of the two components provides high electrochemical activity. A high-performance, transparent and flexible asymmetric supercapacitor was made of the nanocomposite positive electrode and worked in a wide voltage window of 1.2 V. An area capacitance of 48.1 mF/cm2 and an energy density of 9.62 µWh/cm2 at a power density of 28.9 µW/cm2 were achieved. After a 10,000 cycles, the capacitance of the device retains about 90% of its initial value. The high integrated electrochemical performances of the device were attributed to higher storage and transport capacity of the nanocomposite for both ions and electrons. These findings make amorphous and crystalline transition metal oxide nanocomposites as advanced electrode materials for transparent and flexible supercapacitors.

Control the switching mode of Pt/HfO2/TiN RRAM devices by tuning the crystalline state of TiN electrode

In order to increase the resistive switching performance of memory devices based on TiN electrode, it is desirable to fabricate TiN with good oxygen reservoir ability. In the present paper, we report that the crystallized (200) textured TiN electrode were achieved by epitaxial grown on CrRu intermediate layer, which had better oxygen reservoir ability than the amorphous TiN. It is found that the Pt/HfO2/TiN devices with crystallized TiN electrode exhibited a typical bipolar resistive switching behavior, while the I-V curves of the Pt/HfO2/TiN devices with amorphous TiN electrode showed the unipolar resistive switching behavior regardless of voltage polarity, which is similar to the Pt/HfO2/Pt devices. It is believed that this originates from the different oxygen reservoir ability of TiN with different fabricating process. Moreover, the RRAM device with the new structure of TiN (amorphous)/HfO2/TiN (crystallized) exhibited the bipolar resistive switching behavior. This further proved the amorphous TiN electrode had poorer ability of oxygen reservoir than crystallized TiN, which was similar to a noble electrode like Pt electrode. Tuning the resistive switching behaviors of RRAM devices by controlling the crystalline state of TiN electrode may offer a method for fabrication of transition metal oxides based RRAM device with good performances.

In situ X-ray absorption fine structure studies of amorphous and crystalline polyoxovanadate cluster cathodes for lithium batteries

Amorphous and crystalline MetfV10 electrodes for lithium ion batteries were prepared by mixing MetfV10 with different binders: polyvinylidenefluoride (PVDF) or polytetrafluoroethylene (PTFE). The amorphous MetfV10 cathode demonstrates a higher specific capacity than the crystalline cathode. The reaction mechanism was studied using in situ X-ray absorption fine structure (XAFS) and impedance measurements. The X-ray absorption near-edge structure (XANES) results exhibited a 10-electron reduction per the formula of MetfV10 during discharge, resulting in a large capacity. Extended X-ray absorption fine structure (EXAFS) analyses suggested a slight expansion in the molecular size of MetfV10. The impedance measurements reveal that an increase of discharge capacities for the amorphous cathode is due to lower resistance than in the crystalline cathode. This study presents a rational selection of amorphous or crystalline cathode materials for high power and high energy density lithium batteries.

Amorphous LiCoO2-based Positive Electrode Active Materials with Good Formability for All-Solid-State Rechargeable Batteries

ABSTRACTAmorphous LiCoO2-based positive electrode materials are synthesized by a mechanical milling technique. As a lithium oxy-acid, Li2SO4, Li3PO4, Li3BO3, Li2CO3, and LiNO3 are selected and milled with LiCoO2. XRD patterns indicate that reaction between LiCoO2 and these lithium oxy-acids proceeds. Amorphization mainly occurs, and several broad peaks attributable to cubic LiCoO2 are observed in all the samples. These amorphous active materials show mixed conductivities of electron and lithium ion. All-solid-state cells using the prepared amorphous active materials and the Li2.9B0.9S0.1O3.1 glass-ceramic electrolyte are fabricated and their charge-discharge properties are examined. The cells with only the 80LiCoO2·20Li2SO4 (mol%) and the 80LiCoO2·20Li3PO4 active materials function as secondary batteries. This is because higher lithium ionic conductivities are obtained in the 80LiCoO2·20Li2SO4 and 80LiCoO2·20Li3PO4 active materials than in the others. The largest capacity is obtained in the cell with the 80LiCoO2·20Li2SO4 active material because of its good formability and high lithium ionic conductivity. In addition, the cell with the 80LiCoO2·20Li2SO4 positive electrode active material shows the better cycle and rate performance than that with the crystalline LiCoO2. It is noted that the amorphization with lithium oxy-acids is a promising technique for achieving a novel active material with better electrochemical performance.

Assessment of Energy Barriers Between ZrCuAlNi Amorphous Metal and Atomic Layer Deposition Insulators Using Internal Photoemission Spectroscopy

The energy barrier heights between an ultra‐smooth amorphous metal electrode, ZrCuAlNi, and several atomic layer deposited (ALD) insulators are measured using internal photoemission (IPE) spectroscopy. ZrCuAlNi–insulator barriers are characterized within metal–insulator–metal (MIM) stacks with Al top contacts and results are compared with the Al/insulator barrier heights. The measured barrier heights at the ZrCuAlNi interface are found to be 3.3, 3.2, 3.0, and 2.2 eV for SiO2, Al2O3, HfO2, and ZrO2, respectively. This barrier height trend is consistent with the electron affinity of the respective oxides. However, barriers for SiO2 and Al2O3 are smaller than that ideally expected based on the reported vacuum work function of ZrCuAlNi, indicating a smaller ZrCuAlNi effective work function in these device structures. The measured Al barrier height results confirm previous reports of a negative dipole at the Al–ALD insulator interface.

Lithium insertion into silicon electrodes studied by cyclic voltammetry and operando neutron reflectometry.

Operando neutron reflectometry measurements were carried out to study the insertion of lithium into amorphous silicon film electrodes during cyclic voltammetry (CV) experiments at a scan rate of 0.01 mV s-1. The experiments allow mapping of regions where significant amounts of Li are incorporated/released from the electrode and correlation of the results to modifications of characteristic peaks in the CV curve. High volume changes up to 390% accompanied by corresponding modifications of the neutron scattering length density (which is a measure of the average Li fraction present in the electrode) are observed during electrochemical cycling for potentials below 0.3 V (lithiation) and above 0.2 V (delithiation), leading to a hysteretic behaviour. This is attributed to result from mechanical stress as suggested in the literature. Formation and modification of a surface layer associated with the solid electrolyte interphase (SEI) were observed during cycling. Within the first lithiation cycle the SEI grows to 120 Å for potentials below 0.5 V. Afterwards a reversible and stable modification of the SEI between 70 Å (delithiated state) and 120 Å (lithiated state) takes place.

Amorphous titanic acid electrode: its electrochemical storage of ammonium in a new water-in-salt electrolyte.

We report an amorphous titanic acid of TiO1.85(OH)0.30·0.28H2O as a new electrode for aqueous ammonium-ion batteries, which operates in a new water-in-salt electrolyte-25 m NH4CH3COO. The titanic acid electrode exhibits a specific capacity nearly 8 times that from the crystalline TiO2 electrode. In electrochemical reactions, the amorphous titanic acid provides abundant storage sites in its disordered structure and affords strong H-bonding toward the inserted NH4+ ions.

Characterization of sulfur nanocomposite electrodes containing phosphorus sulfide for high-capacity all-solid-state Na/S batteries

All-solid-state Na/S cells with high safety, capacity, and low material costs are desirable for smart grid systems. We report sulfur composite electrodes prepared by the mechanical milling of sulfur, Ketjen black, and P2S5 or Na3PS4 for high-capacity cells. A cell using P2S5, which is not ion conductive, in the sulfur electrode exhibits a high reversible capacity of 340mAh (g‑sulfur electrode)−1 at 0.04C rate at 25°C, which is much larger than that (37.3mAh (g‑sulfur electrode)−1) obtained in a conventional cell using a high ion-conductive Na3PS4 electrolyte. To investigate the reaction mechanism of the sulfur composite electrode containing P2S5, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements and scanning and transmission electron microscopy (SEM/TEM) observations of the electrodes were conducted. The results indicate that a crystalline Na3PS4 component is automatically produced by the electrochemical reaction with Na in the amorphous S-P2S5 electrode and it mixing with the sulfur redox parts at the nanoscale. The mixing degree is higher than that at microscale in the conventional S-Na3PS4 electrode, which results in the high capacity of the cells containing the S-P2S5 electrode. Partial substitution of P2S5 for SiS2 in the sulfur electrode suppresses the nanocrystallization and further increases the reversible capacity up to 390mAh (g‑sulfur electrode)−1 under 0.04C rate, which is the highest in reported all-solid-state Na batteries to date.

Amorphous liquid metal electrodes enabled conformable electrochemical therapy of tumors.

Electrochemical treatment of tumors (EChT) has recently been identified as a very effective way for local tumor therapy. However, hindered by the limited effective area of a single rigid electrode, multiple electrodes are often recruited when tackling large tumors, where too many electrodes not only complicate the clinical procedures but also aggravate patients' pain. Here we present a new conceptual electric stimulation tumor therapy through introducing the injectable liquid metal electrodes, which can adapt to complex tumor shapes so as to achieve desired therapeutic performance. This approach can offer evident merits for dealing with the complex physiological situations, especially for those irregular body cavities like stomach, colon, rectum or even blood vessel etc., which are hard to tackle otherwise. As it was disclosed from the conceptual experiments that, Unlike traditional rigid and uncomfortable electrodes, liquid metal possesses high flexibility to attach to any crooked biological position to deliver and adjust targeted electric field to fulfill anticipated tumor destruction. And such amorphous electrodes exhibit rather enhanced treatment effect of tumors. Further, we also demonstrate that EChT with liquid metal electrodes produced more electrochemical products during electrolysis. Transformations with the shapes of liquid metal provided an easily regulatable strategy to improve EChT efficiency, which can conveniently aid to achieve better output compared to multiple electrodes. Invivo EChT of tumors further clarified the effect of liquid metal electrodes in retarding tumor growth and increasing life spans.

Interactions of Nanostructured TiO2 with Nonaqueous Electrolytes for Na-Ion Batteries

Current shifts towards renewable energy technologies have increased the drive for high performance and cost effective battery systems. Sodium ion batteries present a promising alternative to the commonly used lithium-ion batteries and offer several benefits such as low cost and high availability. While lithium-ion battery systems have been studied intensively, it has become apparent that the interfacial chemistry differs significantly for sodium ion batteries, even when using the same solvents. In previous work, we have shown that amorphous TiO2 nanotube electrodes are a suitable anode materials for Na-ion batteries. The optimization of electrolytes is important to develop a system with good solubility, high transport properties, electrochemical and interfacial stability. In this work, we have investigated the electrochemical properties of TiO2 nanotube electrodes - as a model system - in various electrolytes containing different solvent mixtures (cyclic and acyclic carbonates) with NaClO4 and NaPF6 salt. In addition, we have conducted fundamental studies of chemical, thermal, and electrochemical stability of the chosen sodium-based electrolytes with a phosphazene-based additive FM2 as well as the commonly used FEC additive.

Conformal Vanadium Oxides Beyond Crystalline V2O5 As High Energy Density 3D Thin-Film Electrodes for Lithium-Ion Batteries

The nearly unmatched conformality of Atomic Layer Deposition (ALD) renders it a powerful deposition technique for applications such as catalysis where high surface areas are critical, or for protective coatings on complex 3D surfaces such as powders or porous materials. In the last decade, ALD for energy storage has come into view. Advances in technology have pushed the requirements of energy storage devices, leading to novel lithium-ion battery (LIB) concepts such as 3D-structured electrodes, thin-film electrode and the combination of both. These concepts enable high-power and high-energy integrateable batteries, but require a conformal deposition technique for the current collectors, electrodes, solid electrolytes and interfacial coatings alike. Besides 3D structuring, materials design of the LIB electrodes is paramount to achieve higher power and higher energy densities, beyond traditional electrode materials such as LiCoO2, and LiMnO2which are limited to volumetric capacities of 550-700mAh/cm³. Traditionally, the main focus of materials development for batteries has been on crystalline compounds. However, several indications exist that higher energy and power density can be found in amorphous materials. ALD is not only excellently suited to deposit conformal films, but also able to grow high-quality amorphous films at low deposition temperatures, enabling the study of amorphous thin-film electrodes. In this work, ALD of vanadium oxides for applications as lithium-ion electrodes is envisioned. Vanadium oxides were amongst the first materials to be studied as LIB cathodes, but were never commercialised. V2O5 is a well-known LIB electrode, but the rather low volumetric energy density (when storing one lithium) or poor cyclability (when storing 2-3 lithium ions) have prevented its large-scale commercialisation in the past. Here, we demonstrate the ALD deposition of amorphous and crystalline V2O5, and two ‘flavours’ of amorphous VO2, from a single vanadium precursor (Tetrakis[ethylmethylamino] vanadium). We demonstrate the crystallisation of these films into crystalline films in the Wadsley series, and are able to unravel the influence of initial ALD process, atmosphere, temperature and substrate on the crystallization and oxidation of the VO2 films. With this in mind, we are able to obtain phase-pure crystalline vanadium oxides in the whole Wadsley series (VO2–V6O13–V4O9–V3O7–V2O5), which show very high energy densities up to more than double that of typical bulk cathodes (1380mAh/cm³ for V4O9). The amorphous initial states (amorphous VO2 and V2O5) are often not considered due to their lack of a clearly defined electrode potential. However, building on the nature of ALD to grow high-purity amorphous films, these were also investigated here. It was found that, besides also having very high capacities, their kinetics are excellent. Finally, the best candidates were examined on an ALD Pt-coated silicon micropillar array as 3D-structured thin-film electrodes. The 20x surface enhancement of the micropillar substrate enhanced the footprint capacity of the 40nm films from approximately 2-5µAh/cm² to 40-100µAh/cm², with the highest capacity for amorphous VO2(>100µAh/cm² for the 40nm film), while at the same time maintaining the excellent thin-film kinetics of the planar films, in effect simultaneously demonstrating the potential of ALD to deposit 3D thin-film electrodes as well as a tool to study amorphous and crystalline films. In conclusion, a wide range of crystalline and amorphous vanadium oxides were demonstrated from a single vanadium-precursor based ALD process. All films were examined as potential lithium-ion battery electrodes, and showed promise of very high volumetric capacities. In particular, the amorphous films and the crystalline VO2 (B) not only displayed very high capacities, but also excellent kinetics, enabling both high-energy and high-power electrodes. Figure 1

Enhanced Cycleability of Amorphous MnO₂ by Covering on α-MnO₂ Needles in an Electrochemical Capacitor.

An allomorph MnO2@MnO2 core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N2 adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO2 nano-sheets which were well grown onto the surface of α-MnO2 nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic pseudo-capacity of the MnO2@MnO2 capacitor electrode contributed to a specific capacitance of 150.3 F·g−1 at a current density of 0.1 A·g−1. Long cycle life experiments on the as-prepared MnO2@MnO2 sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g−1. This retention value was found to be significantly higher than those reported for amorphous MnO2-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO2@MnO2 was due to the supporting role of α-MnO2 nano-needle core and the outer amorphous MnO2 layer.

Amorphous carbon thin film electrodes with intrinsic Pt-gradient for hydrogen peroxide detection

Nanoscale amorphous carbon thin films with intrinsic Pt gradient show great promise as new electrode materials for electrochemical detection of hydrogen peroxide. Embedding the Pt particles in the carbon matrix during the fabrication process allows tighter integration than, for example, adding them after the fabrication on top of the substrate. Especially, this approach can offer excellent electrochemical properties combined with CMOS compatibility, which is crucial for further device development. Here we provide extensive in depth electrochemical and physicochemical characterization of these novel materials by cyclic voltammetry (CV), chronoamperometry (CA), rotating disk electrode (RDE) experiments, transmission electron microscopy (TEM), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Equipped with these detailed results on these materials we proceed to present some suggestions how the physicochemical properties correlate with the results from electrochemical measurements. (i) It is shown that coarsening of the initially very finely dispersed structure occurs both under electron bombardment during TEM imaging as well as during cyclic voltammetry in H2SO4. (ii) Further, it is shown that OH is adsorbed on small Pt islands much more strongly compared to the bulk Pt, which may heavily influence hydrogen peroxide redox reactions on these Pt-containing amorphous carbon films. (iii) Finally, we proceed to demonstrate that despite these complications, these materials show linear response for hydrogen peroxide reduction in neutral phosphate buffered saline combined with very fast response times.