Positive Electrode Potentials Research Articles

Zero volt storage of Na-ion batteries: Performance dependence on cell chemistry!

Sodium-ion batteries (NIBs) are regaining their importance in recent years as a sustainable complementary energy storage device for Li-ion batteries. Although, they cannot compete in terms of energy density with respect to Li-ion, they present a few advantages, namely the 0 V stability that makes them safe during external short and/or over-discharge. When the cell is discharged to 0 V, the negative electrode potential shoots up high during which the copper current collector in use for Li-ion cells could oxidize, dissolve and leads to internal short. In contrast, Na-ion cells utilize an aluminium current collector that is strongly resistant against oxidation, hence enabling their 0 V stability. However, apart from the current collector stability, the negative electrode potential rise could cause interphase instability which is not well elucidated. Hence, herein, we explored two different Na-ion chemistries, namely polyanionic Na3V2(PO4)2F3-hard carbon and sodium layered oxide-hard carbon using different electrolyte formulations. Combined impedance analyses, ex-situ X-ray photoelectron spectroscopy (XPS) and operando optical sensing indicate the 0 V discharge involves SEI degradation thereby deteriorating the cell performance, the extent of which depends on the positive electrode potential and the electrolyte in use. Overall, the 0 V stability is not an in-built property of Na-ion cells and a careful selection of cell chemistry is mandatory to achieve 0 V stable Na-ion cells.

Dealloying of Ni- and Fe-Based Alloys in Boiling Caustic Environments and the Parameters Influencing the Geometry of a Dealloyed Layer

Nickel alloys and stainless have been the material of choice for a wide range of industrial applications like power and petrochemical plants that involve exposure to corrosive environments. For instance, Alloy 800 (Fe-30Ni-20Cr) has been used as the tubing material in CANDU and Siemens steam generators (SGs) for decades with excellent in-service performance. However, despite their good resistance to general to localize corrosion, Ni- and Fe-based alloys are susceptible to environmentally assisted cracking (EAC) in certain environments, such as hot caustic aqueous solutions. Laboratory experiments have shown that these materials are susceptible to dealloying in hot caustic environments due to the selective removal of Fe, Cr and Mo (less noble elements). As a result of dealloying, a brittle nanoporous film forms on the surface that is enriched in Ni (the more noble element). This film has been proposed to act as a precursor to stress corrosion cracking (SCC) by a film-induced cleavage (FIC) mechanism, where the brittle film injects a high speed/energy crack to the substrate material.The fast kinetics of dealloying requires a connected percolating pathway of less noble element atoms to exist within the alloy that extends from the surface into the material. The presence of this pathway depends on the composition of the alloy. The parting limit defines the minimum amount of the more reactive element(s) in a particular alloy system that makes it susceptible to dealloying. Below the parting limit composition, dealloying will be suppressed by surface diffusion of the more noble element, even at very oxidizing potentials, and the surface of the material will show a passive-like behavior (general dissolution would eventually occur at high anodic overpotentials). Besides the alloy composition, dealloying highly depends on the electrode potential. Below a threshold potential (dealloying critical potential), surface diffusion of the more noble element will overcome the dissolution of the less noble element(s) and suppress dealloying.In this study, we examine different factors that affect dealloying and the geometry of a dealloyed layer through electrochemical measurements and nano-scale characterization techniques. Several engineering Ni- and Fe-based alloys were tested in deaerated boiling caustic solutions to understand the effect of alloy composition on the susceptibility to dealloying. Results indicate that an increase in Ni content will shift the dealloying critical potential to more positive potentials and subsequently the resistance to dealloying. Although Ni is the alloying element that provides nobility and resistance in hot caustic environments, our results show that the thermodynamic and kinetic behaviour, and the content of the less noble elements play an important role in these environments. A comparison between different alloys with similar Ni-content but different Cr and Mo contents shows the beneficial and detrimental role of Cr and Mo in dealloying, respectively. The air-formed chromia-based oxide on the surface of alloys with high Cr-content slowly dissolves in the caustic environment, delays the dissolution of less noble elements, and increases the resistance to dealloying.Changes in electrode potential and time of exposure to the caustic environments, alter the geometry of the dealloyed layer. Results show an increase in the diameter and coarsening of ligaments with increasing time of exposure to the caustic environment. Coarsening of ligaments is believed to impair the ability of a dealloyed layer to inject a micro-crack to the underlying material and initiate SCC. Also, results show that an increase in anodic overpotential of only a few millivolts in the vicinity of dealloying critical potential would change the geometry of the dealloyed layer significantly. The surface diffusion of the more noble element (i.e. Ni) cannot keep up with the fast removal of atoms of the less noble elements (i.e. Cr, Mo, and Fe) at more positive electrode potentials compared to the dealloying critical potential which results in a weak bonding at the film/metal interface. The weak bonding may not be able to support the transmission of a high-speed crack to the substrate material, reducing the likelihood of SCC initiation. Figure 1

In Situ Synthesis of AgCl@Ag Plates as Binder-Free Cathodes in a Magnesium Seawater-Activated Battery

A binder-free AgCl@Ag (SPL-A) cathode was prepared via a facile one-step synthesis by the in situ growth of AgCl active material on the surface of Ag foil substrate. Compared with the AgCl cathode (SPL-B) prepared by the traditional smelting-rolling method, the coarse-grained particulates of AgCl in AgCl@Ag cathode facilitated the permeation of the electrolyte. In addition, it exhibited a preferred growth orientation of the (111), (222), and (311) crystal planes to reduce the charge transfer resistance. The electrochemical behaviors of the optimized SPL-A-24 cathode (prepared with reaction time of 24 h) and the SPL-B cathode were also compared. The galvanostatic discharge results showed that SPL-A-24 cathode had a more positive electrode potential than SPL-B cathode (−0.06 V vs −0.19 V at 50 mA cm−2). Moreover, SPL-A cathode exhibited a stable discharge process that SPL-B cathode could not achieve at 100 mA cm−2 and 250 mA cm−2. The magnesium seawater-activated battery assembled with SPL-A-24 cathode displayed a shorter time to reach the voltage plateau (0.2 s), a higher maximum discharge voltage (1.69 V), a larger specific power (255.5 mWh g−1), and higher specific capacity (167.7 mAh g−1) at the discharge current density of 50 mA cm−2.

Overoxidation of Intrinsically Conducting Polymers.

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively.

Influence of heat treatment on tribocorrosion properties of Ni-B composite coatings

Various surface protection technologies, in particular, electrochemical, are used to increase the wear and corrosion resistance of steels and alloys. Composite electrochemical coatings (CEC) technology is more promising than "pure" galvanic coatings. Application of CEC increases the wear, corrosion and fatigue failure resistance of metals. Nickel often is chosen as a CEC matrix because it easily forms uniformly filled defect-free composite structures with many particles of the dispersed phase (DP).
 Physical and mechanical properties of metal coatings determine practical application of such composition. The characteristics of nickel-based CEC are: high hardness and strength, significant corrosion resistance in atmospheric environment, as well as in alkali and mild acidy environments. An effective composition coating with tribological designation can be CEC Ni-B, received in the process of electrolysis from suspension of amorphous boron in nickel electrolyte. A new composite structure of matrix filled type Ni-Ni3B is formed after heat treatment. Composition and structure of coating is determined by regimes of diffusion annealing. Ni-B coatings increase wear resistance of steel in chlorine-based environments. The influence of low-temperature thermal treatment of Ni-B CEC on steel 09Mn2Si on their tribocorrosion behavior is investigated. It is shown that the structural factor has a decisive influence on the efficiency of such friction pairs. The CEC has the least wear and the most positive compromise electrode potential after vacuum annealing at 450°C, when the initial stage of solid-phase interaction of coating components with the formation of Ni-Ni3B occurs.

Rate-controlling element in the self-discharge process in electrochemical double-layer capacitors

Suppression of self-discharge is crucial in the development of electrochemical double-layer capacitors (EDLCs). In this study, the rate-controlling element of the self-discharge process in EDLCs was explored without any new additives, and the anion was found to play a critical role in this process. The thickness ratio between the positive and negative electrodes (P/N ratio) was the primary factor used to control the self-discharge rate. As the P/N ratio increased, the anion density in the positive electrode decreased. The P/N ratio was increased to retain the anions for a longer period in the cell, which caused self-discharge suppression and led to a slow change in the positive electrode potential when held at an open-circuit status. Cells with a P/N ratio of 1.37 showed 26 to 32% reduced voltage decay than did those with a P/N ratio of 1.00 after 70 h.

Towards reliable three-electrode cells for lithium-sulfur batteries.

Three-electrode measurements are valuable to the understanding of the electrochemical processes in a battery system. However, their application in lithium-sulfur chemistry is difficult due to the complexity of the system and thus rarely reported. Here, we present a simple three-electrode cell format with relatively good life time and minimum interference with the cell operation.

Bubble formation behavior in hydrogen supply system using lithium metal

When a lithium-air battery is discharged, lithium ions normally react with oxygen at the positive electrode, but when the positive electrode potential drops significantly, water in the electrolyte reacts with lithium ions to generate hydrogen. In this study, we proposed a new system for high-density energy storage and hydrogen supply using lithium by utilizing the structure of lithium-air batteries and this working principle, and conducted basic experiments. As a result, it was confirmed that a large overvoltage is involved for the hydrogen production reaction compared to the theoretical potential. In addition, the formation behavior of hydrogen bubbles was observed, and it was confirmed that the almost spherical bubbles were generated in this experimental system. In the future, we will investigate the detailed causes of the overvoltage and hydrogen production behavior in the hydrogen production reaction and propose methods to reduce the overvoltage in order to improve the efficiency of hydrogen production.

Fe2(MoO4)3 assembled by cross-stacking of porous nanosheets enables a high-performance aluminum-ion battery.

Rechargeable aluminum-ion batteries have attracted increasing attention owing to the advantageous multivalent ion storage mechanism thus high theoretical capacity as well as inherent safety and low cost of using aluminum. However, their development has been largely impeded by the lack of suitable positive electrodes to provide both sufficient energy density and satisfactory rate capability. Here we report a candidate positive electrode based on ternary metal oxides, Fe2(MoO4)3, which was assembled by cross-stacking of porous nanosheets, featuring superior rate performance and cycle stability, and most importantly a well-defined discharge voltage plateau near 1.9 V. Specifically, the positive electrode is able to deliver reversible capacities of 239.3 mA h g-1 at 0.2 A g-1 and 73.4 mA h g-1 at 8.0 A g-1, and retains 126.5 mA h g-1 at 1.0 A g-1 impressively, after 2000 cycles. Furthermore, the aluminum-storage mechanism operating on Al3+ intercalation in this positive electrode is demonstrated for the first time via combined in situ and ex situ characterization studies and density functional theory calculations. This work not only explores potential positive electrodes for aluminum-based batteries but also sheds light on the fundamental charge storage mechanism within the electrode.

Nickel Cobaltite: A Positive Electrode Material for Hybrid Supercapacitors.

The increased demand of energy due to the recent technological advances in diverse fields such as portable electronics and electric vehicles is often hindered by the poor capability of energy-storage systems. Although supercapacitors (SCs) exhibit higher power density than state-of-the art batteries, their insufficient energy density remains a major challenge. An emerging concept of hybrid supercapacitors (HSCs) with the combination of one capacitive and one battery electrode in a single cell holds a great promise to deliver high energy density without sacrificing power density and cycling stability. This Minireview elaborates the recent advances of use of nickel cobaltite (NiCo2 O4 ) as a potential positive electrode (battery-like) for HSCs. A brief introduction on the structural benefits and charge storage mechanisms of NiCo2 O4 was provided. It further shed a light on composites of NiCo2 O4 with different materials like carbon, polymers, metal oxides, and others, which altogether helps in increasing the electrochemical performance of HSCs. Finally, the key scientific challenges and perspectives on building high-performance HSCs for future-generation applications were reviewed.

Modeling Electrochemical Transport within a Three-Electrode System Towards Fast Charge and Discharge Applications

In support of GM’s traction battery efforts, we derive and implement a method to describe the electrochemical performance of a battery cell through the combination of a modified Newman Pseudo 2-Dimensional model and a three-electrode experimental apparatus. To assess the capability of the method, we compare model results with experimental data for a lithiated graphite and lithium nickel manganese cobalt oxide system. The model is applied to simulate the electrochemical and transport processes within the battery cell to predict the negative electrode potential and positive electrode potential with respect to a lithium iron phosphate reference electrode, as well as the terminal voltage.We extend this discussion to cover applicability to fast charge considerations to avoid lithium plating at the anode during a fast charge event.

Hydrate Melt Electrolyte for Aqueous K-Ion Batteries

Recently, alkali metal hydrate melts, which are molten hydrated salts at room temperature, have attracted attention as electrolytes realizing high-voltage aqueous batteries.1 K+ ion has a smaller Stokes radius than that of Li+ ion due to weaker interaction with water molecules. Thus, K hydrate melt electrolytes demonstrate higher ionic conductivity than the Li ones.1 Our group and Ko et al. reported a new K hydrate melt mixing two anions, bis(fluorosulfonyl)amide (FSA−) and trifluoromethanesulfonate (OTf−).2,3 However, electrochemical performance and reaction mechanism of K+ ion insertion materials in the hydrate melt is not fully understood, and the demonstration of high-voltage aqueous KIBs is still challenging. In this study, we investigate electrochemical performance of potential K+ insertion materials, such as Prussian blue analogues and organic compounds, for high-voltage aqueous K-ion battery (KIB).A series of K(FSA)1-x (OTf) x ·nH2O were prepared at room temperature to check formation of hydrate melt. The electrochemical stability windows were examined by linear sweep voltammetry (LSV). Pt and Al foils were used as working electrodes to evaluate anodic and cathodic stability, respectively. Galvanostatic charge/discharge tests of K2Fe0.5Mn0.5[Fe(CN)6] and 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which is a potential positive electrode and negative electrode, respectively, for aqueous KIBs,4 were conducted with three-electrode cells assembled with activated carbon as a counter electrode. An aqueous K-ion full cell was fabricated by combining the positive electrode and negative electrode in the weight ratio of 1:2.1.Among the prepared K(FSA)1-x (OTf) x ·nH2O solution, K salts monohydrate melt of K(FSA)0.6(OTf)0.4·1.0H2O contains the least H2O content. Figure 1a displays the LSV curves in the electrolytes of K(FSA)0.6(OTf)0.4·1.0H2O and the endmembers of KFSA·1.8H2O and KOTf·2.8H2O. KFSA·1.8H2O and KOTf·2.8H2O had a potential window of 2.67 V and 2.01 V, respectively. On the other hand, K(FSA)0.6(OTf)0.4·1.0H2O exhibited that of 2.89 V, which was much wider than KFSA·1.8H2O and KOTf·2.8H2O. In KOTf·2.8H2O, K2Fe0.5Mn0.5[Fe(CN)6] electrode delivered a low initial capacity of 53 mAh g-1 at the initial cycle and capacity degradation over 50 cycles (Fig. 1b, top). In contrast, the electrode delivered a higher initial capacity of 124 mAh g-1 in K(FSA)0.6(OTf)0.4·1.0H2O and better cycle performance (Fig. 1b, bottom) than that in KOTf·2.8H2O. Similar to the positive electrode, the PTCDI electrode exhibited continuous capacity degradation in KOTf·2.8H2O (Fig. 1c, top), whereas the electrode delivered an excellent cycle performance in K(FSA)0.6(OTf)0.4·1.0H2O over 200 cycles (Fig. 1c, bottom). Figure 1d compares charge/discharge curve of PTCDI//K2Fe0.5Mn0.5[Fe(CN)6] full cells filled with KOTf·2.8H2O and K(FSA)0.6(OTf)0.4·1.0H2O. The K(FSA)0.6(OTf)0.4·1.0H2O cell demonstrated a much better cycle performance over 50 cycles than that in KOTf·2.8H2O. The PTCDI//K2Fe0.5Mn0.5[Fe(CN)6] full cell exhibited average voltage of 1.5 V. Moreover, K(FSA)0.6(OTf)0.4·1.0H2O electrolyte realized 2 V-class aqueous KIBs by selecting a proper negative electrode material. In addition, we will discuss charge/discharge mechanism including insertion species of K2Fe0.5Mn0.5[Fe(CN)6] and PTCDI.

Studies on Electrochemistry and Factors Affecting Phase Transition Behavior of LiMnO2 Polymorphs

Co/Ni-free high energy density materials are necessary as positive electrode materials of lithium-ion batteries for electric vehicles. Therefore, electrode materials made from abundant manganese ions are attractive candidates. LiMnO2 with an orthorhombic zigzag layered structure has been studied as potential positive electrode materials. However, LiMnO2 delivers a large reversible capacity after continuous charge/discharge cycles associated with the spinel-like phase transition. In contrast, a non-layered system, cation-disordered rocksalt-type LiMnO2 prepared by mechanical milling shows slow phase transition kinetics to the spinel-like phase on electrochemical cycles.1 In this study, we have synthesized two different polymorphs of LiMnO2 by heat-treatment of rocksalt LiMnO2 and ion-exchange reaction of NaMnO2 with an α-NaFeO2-type layered structure,2 and tested as electrode materials. These different polymorphs show unique phase transition behavior, and from these results, factors affecting electrode performance of LiMnO2 are discussed. X-ray diffraction patterns of different polymorphs of LiMnO2 are shown in Figure 1. The low crystallinity sample with the rocksalt structure obtained by mechanical milling crystallizes into the sample with well-defined diffraction lines after heat-treatment, but the sample clearly shows different diffraction patterns compared with both orthorhombic and α-NaFeO2-type layered phases. Electrochemical properties of LiMnO2 with different crystal structures are compared in Figure 2. Among the tested LiMnO2 polymorphs, the heat-treated sample of rocksalt LiMnO2 delivers a large reversible capacity of 250 mA h g-1 with the highest average discharge voltage. Different polymorphs shows different behavior related to phase transition kinetics and voltage hysteresis on electrochemical cycles. Phase transition kinetics are clearly influenced by original crystal structures and cation distributions. From the results, we discuss the factors affecting electrode properties and phase transition kinetics during charge/discharge processes for the LiMnO2 polymorphs, and the possibility of the development of Ni/Co-free high capacity electrode materials.References Sato et al., and N. Yabuuchi, J. Mater. Chem. A, 6, 13943 (2018).J. Paterson et al., J. ElectroChem., 151 (10) , A1552-A558 (2004) Figure 1

(Invited) Oxide- and Polyanion- based Cathode Materials for Li-ion and Na-ion Batteries

Na- ion layered oxide as cathodes have attracted both the scientific community and industry. They offer high gravimetric energy density, tunability of properties and ease of synthesis. This leads to both interesting science and low cost applied materials.Layered oxides are generally classified by the nomenclature introduced by Delmas et. al.1 which depends on the alkali environment and stack of layers in the unit cell. The same team also used layered oxides for the first-time as potential positive electrode for reversible sodium storage.2 In this talk we present our contributions on (i) O3, (ii) P3 and (iii) modified P3 type layered oxides as cathode materials for Na-ion batteries.O3-type layered sodium transition metal oxides (NaxMO2, M = transition metal ions) are one of the most attractive cathode materials considering their capacity. However, the use of O3 phases is limited due to their low redox voltage and several associated phase changes which are unfavorable for long cycling. 3-5 In this presentation, we show the effect of Cu, Ni and Ti doping in the O3 structure and relate the observed local environments to their storage performances. Cu2+ Jahn-Teller distortion leads to irreversibility and dictates the amount of Cu2+ that can be doped in the layer. Our results show that 10-12% of Cu-doping is optimal. In order to further examine the effect of local structures, we doped Ni2+ and achieved excellent structural reversibility which favors high-rate performance and cycling stability. 6 Na-sufficient Fe and Mn based P3 layered oxide is able to accommodate higher than 0.67 moles of Na-ions. 7,8 We present the effects of voltage limits on the storage performances and highlight associated phase changes during electrochemical cycling. XANES data confirm the charge compensation mechanism during electrochemical cycling. Full cell data further elucidate the sufficiency of Na-ions in the P3 structure. 8 Lastly, the storage performances of P3-Na0.9Fe0.5Mn0.5O2 are compared with those for modified P3 phase, P3 (major)/ O3 (minor) layered oxide. The phase changes during cycling and comprehension of charge compensation mechanism from XANES of this modified P3 structure are reported.

A two-dimensional transient model for a zinc-cerium redox flow battery validated by extensive experimental data

A two-dimensional transient model accounting for the charge, mass and momentum transport coupled with electrode kinetics is developed for zinc-cerium redox flow batteries (RFBs). The model is validated against an extensive set of experimental data obtained in our laboratory. This includes full-cell voltages, positive and negative electrode potentials monitored against reference electrodes inserted into the battery half-cell compartments and Ce(IV) concentrations in the positive electrolyte over 5 cycles. To the best of our knowledge, this is the most comprehensive set of experimental data used to fit and validate a flow battery model. The validated model is then used to predict the cell voltages and limiting redox reactions during battery operation for different model parameters to provide a guide to further improve the performance of zinc-cerium RFBs.

Asymmetric response of interfacial water to applied electric fields.

Our understanding of the dielectric response of interfacial water, which underlies the solvation properties and reaction rates at aqueous interfaces, relies on the linear response approximation: an external electric field induces a linearly proportional polarization. This implies antisymmetry with respect to the sign of the field. Atomistic simulations have suggested, however, that the polarization of interfacial water may deviate considerably from the linear response. Here we present an experimental study addressing this issue. We measured vibrational sum-frequency generation spectra of heavy water (D2O) near a monolayer graphene electrode, to study its response to an external electric field under controlled electrochemical conditions. The spectra of the OD stretch show a pronounced asymmetry for positive versus negative electrode charge. At negative charge below 5×1012 electrons per square centimetre, a peak of the non-hydrogen-bonded OD groups pointing towards the graphene surface is observed at a frequency of 2,700per centimetre. At neutral or positive electrode potentials, this 'free-OD' peak disappears abruptly, and the spectra display broad peaks of hydrogen-bonded OD species (at 2,300-2,650per centimetre). Miller's rule1 connects the vibrational sum-frequency generation response to the dielectric constant. The observed deviation from the linear response for electric fields of about ±3×108volts per metre calls into question the validity of treating interfacial water as a simple dielectric medium.

Calendar Vs. Cycle Aging of Lithium-Ion Cells with Silicon Anode

Silicon has been investigated for decades, as an alternative to the graphite used in lithium-ion battery anodes, because of its high theoretical capacity. However, the large volume change of Si during electrochemical cycling (cycle-aging) deteriorates the solid electrolyte interphase (SEI) layer on the particles, resulting in increased electrolyte reduction reactions and associated capacity decay. Capacity fade is also observed in cells that are not cycled but simply held at voltage for extended periods of time (calendar-aging). [1]Here we report the calendar and cycle-aging behavior of cells with a Si anode that is paired with a NMC532 cathode (Figure 1). The tests were conducted in coin cells and in cells with a reference electrode (prepared by in-situ lithiation of a 25 mm Cu wire). This reference electrode allowed us to determine changes in the individual electrode profiles during aging and to examine impedance changes that were monitored via hybrid pulse power characterization (HPPC) tests. [2]Our various experiments have revealed the following: (i) capacity-fade is greater during cycle-aging than during calendar-aging; (ii) the capacity fade is associated with shifts in both positive and negative electrode potentials; (iii) parasitic currents are observed during the calendar-life hold, which indicate ongoing electrolyte reduction reactions at the silicon electrode; (iv)both electrodes contribute to the significant impedance rise observed during cell aging.To further examine sources of the observed performance degradation we conducted experiments with cells with the Si paired with LiFePO4. These data, along with the probable mechanisms of cell aging, will also be discussed during the presentation.References Kalaga et al., Acta 2018, 280, 221-228. Klett et al., Electrochem. Soc. 163 (2016) p. A875. Acknowledgments: M.L. acknowledges the generous grants from the U.S. National Science Foundation with the award numbers of CMMI-1660572 and IIP-1918991 that enabled her research at Argonne National Laboratory. The electrodes and electrolytes used in this study are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility. We are grateful to Andrew Jansen, Bryant Polzin, and Steve Trask for their assistance during this study. Figure 1

In Situ tem Cycling of Semi-Solid State Micro-Battery in Liquid Electrolyte

All solid state Li-ion micro-battery is a promising candidate to power miniaturized sensors for Internet of things (IOT) and other electronic devices. In recent times, the spinel LiMn1.5Ni0.5O4 (LNMO) has demonstrated as a potential positive electrode material for Li-ion thin film batteries offering a theoretical capacity of 147 mAh/g (65 µAh/cm2/µm for a bulk density of 4.47 g/cm3) and operates up to now at the highest potential (around 4.7 V vs. Li+/Li) [1]. In this work, we report our first successful in situ TEM attempts to observe the morphological, structural and interfacial changes in the positive electrode layer of FIB prepared sample which undergo after cycling using liquid electrolyte. More precisely we compared the morphological and structural evolution between a pristine and cycled microbattery by 4D STEM-ASTAR technique to highlight the key information to improve the deposition conditions that will enhance the reliability and production quality of such micro power devices. The in situ cycling in liquid TEM has given this opportunity to study the battery electrode materials so as to spot the slightest modifications of the materials resulting in important advances in knowledge on electrochemical energy storage [2-3].Here, our approach is based on the cycling a FIB lamella sample inside the TEM using liquid-electrochemical TEM holder with conventional liquid electrolyte (1M LiClO4, EC: DMC 1:1). The cross-section image of as prepared FIB sample with homogeneous deposition of distinctive layers of different thickness [from bottom to top-Si (0.385mm)/ Al2O3 (100nm)/ Pt (630nm) / LNMO (400nm)] is shown in figure 1a. The Pt current collector of FIB lamella sample is connected to the Pt working electrode on the e-chips used for TEM study (figure 1b). First, using FIB preparation technique, we sliced a full 2-D “thin film micro-battery” making it as thin to observe/analyse under TEM. Then, we modified the FIB lamellar design using FIB-SEM tool to get good electrical contact and reduced polarisation. Several technological problems have to be overcome in the process. For the instance, it is mandatory to obtain a good electrical contact between the Pt working electrode of e-chip and Pt current collector of FIB lamellar, which is later achieved by depositing extra Pt between the two contacts forming a platinum bridge. A 4-Probe electrical conductivity performed locally confirms the good electrical contact between the as prepared FIB lamella sample and Pt working electrode of e-chip. The cross-section bright field TEM image of a final modified version of FIB lamella sample used in the study is shown in figure 1d.The FIB lamella sample is then later cycled inside the liquid electrochemical TEM holder (fig 1c) in potential window of 4.1 V-4.8 V vs. Li+/Li. The flow of the electrolyte (LiClO4 EC:DMC 1:1) inside the TEM holder was further controlled by microfluidic controller with the flow rate of 2 µL/min. CV was recorded at a sweep rate of 0.1mV/s and two plateaus at 4.4 V and 4.6 V was observed corresponding to Ni2+/3+ and Ni3+/4+ oxidation respectively (Fig 1f). The basic redox steps observed during the charge are same as observed in the case of cycling bulk 2D thin film in a homemade flat cell.The comparison between the cycled and pristine microbattery sliced by FIB and observed by TEM allowed us to clearly demonstrate the formation of cracks inside the LMNO layer, loss of contact between the LMNO layer and the platinum current collector, as well as the agglomeration of the organic compounds produced due to the electrolyte decomposition. Moreover, 4D STEM-ASTAR technique provided us with the crucial information regarding the grain size reduction from 20 nm in pristine to 12 nm in cycled sample, confirming the continuous electrode-electrolyte reaction happening over the cycling. Also, the decrease in crystallinity and increase in the amorphization of the LMNO grains by 38 % in the cycled sample compared to pristine as shown in figure 1e and g clearly prove the fast capacity fading phenomenon observed in bulk microbattery. Furthermore, a thickness of ~20nm along the platinum layer, a (111) preferred orientation is observed exhibiting the epitaxial effect of LMNO on platinum layer which has been further supported by the precision electron diffraction (PED) recorded on both LMNO and platinum grains.

Aluminum current collector for high voltage Li-ion battery. Part II: Benefit of the En’ Safe® primed current collector technology

This paper reports the benefits of a carbon coated aluminum current collector specifically designed to promote LiNi1.5M1.5O4 (LNMO) as high potential positive electrode material. This underlayer allows efficient protection of the aluminum surface in 1 M LiTFSI/[EC/DMC] electrolyte for more than 100 cycles (C/2–D/2) in experimental conditions mimicking the electrochemical response of LNMO. The design of such coating appears therefore as a very encouraging strategy to make the use of imide-based electrolytes possible despite their corrosive properties towards aluminum. The as-developed carbon coating also reduces the interfacial impedance of an LNMO-based electrode by a factor of 5 in 1 M LiPF6/[EC/DMC] electrolyte therefore paving the way to accelerate the industrial deployment of safe “5V” Li-ion batteries.

Iodine adlayer mediated gold electrooxidation in bis(trifluoromethylsulfonyl)amide-based ionic liquids

Conventional complexing ligands for the wet etching of gold are hazardous, making large-scale utilization problematic. In particular, the environmental risks caused by these materials must be minimized. To address this problem, an electrochemical etching method for gold using bis(trifluoromethylsulfonyl)amide ([Tf2N]–)-based ionic liquids (ILs) has been developed. Here, only one layer of conventional complexing ligand, that is, iodine on gold, is required to achieve the continuous dissolution of gold under a positive electrode potential. In addition, the etching behavior involves sacrificial anode electrolysis (SAE) to generate gold nanoparticles (AuNPs). It was found that the electrochemical oxidation of gold is strongly dependent upon the type of halide ion, and the iodine-modified gold electrode produced a large oxidation peak in [Tf2N]–-based ILs. The voltammetric profiles of iodine-modified gold electrodes reveal that the electronic charge consumed during the electrochemical oxidation is affected by the IL cation and the crystallographic orientation of gold, increasing as ammonium < imidazolium < pyrrolidinium and Au(111) < Au(100) < Au(110), respectively. Of the IL anions evaluated in this study, the apparent oxidation peak was only observed for iodine-modified gold electrode in [Tf2N]–-based ILs, suggesting that [Tf2N]– anions promote gold complexation and act as ligands. Further, microscopic and spectroscopic measurements provide evidence of gold dissolution after electrochemical oxidation and the formation of gold complexes, followed by the generation of AuNPs. The results reveal a mechanism for the iodine-catalyzed electrochemical oxidation of gold in [Tf2N]–-based ILs. The electrolysis of gold in the ILs reported here opens avenues for acquiring novel aurate salts with IL anions and AuNPs.