Ex-situ Scanning Electron Microscopy Research Articles

The dynamic evolution of aggregated lithium dendrites in lithium metal batteries

Lithium (Li) metal anodes promise an ultrahigh theoretical energy density and low redox potential, thus being the critical energy material for next-generation batteries. Unfortunately, the formation of Li dendrites in Li metal anodes remarkably hinders the practical applications of Li metal anodes. Herein, the dynamic evolution of discrete Li dendrites and aggregated Li dendrites with increasing current densities is visualized by in-situ optical microscopy in conjunction with ex-situ scanning electron microscopy. As revealed by the phase field simulations, the formation of aggregated Li dendrites under high current density is attributed to the locally concentrated electric field rather than the depletion of Li ions. More specifically, the locally concentrated electric field stems from the spatial inhomogeneity on the Li metal surface and will be further enhanced with increasing current densities. Adjusting the above two factors with the help of the constructed phase field model is able to regulate the electrodeposited morphology from aggregated Li dendrites to discrete Li dendrites, and ultimately columnar Li morphology. The methodology and mechanistic understanding established herein give a significant step toward the practical applications of Li metal anodes.

Combination of in-situ ion beam analysis and thermal desorption spectroscopy for studying deuterium implanted in tungsten

We demonstrate a combinatorial approach integrating ion implantation followed by thermal annealing and simultaneous in situ ion beam analysis with thermal desorption spectroscopy in a single set-up. Atomic and molecular deuterium ions of 3 keV were implanted into bulk tungsten with doses exceeding 1 × 1022 ions m−2. Depth profiling of both, protium and deuterium was performed by elastic recoil detection analysis, while simultaneously the outgassing rates of molecular deuterium by thermal desorption spectroscopy were monitored during temperature ramps from room temperature to ≈1400 K. The combination of the two techniques in situ is shown capable to identify the distinct retention behavior of deuterium at different temperatures and in different reservoirs, e.g. located close to the surface and diffused deep into the material. Ex-situ scanning electron microscopy confirmed blister formation, and recovery of the initial surface morphology after high temperature annealing, in analogy to comprehensive ex-situ studies.

Mechanical behaviour of Li3xLa1/3−xNbO3 with domain structure

This study investigates the mechanical behaviours of A-site deficient perovskite-type Li3xLa1/3−xNbO3 electrolytes (3x = 0.00–0.18) with domain structures. The samples were examined under uniaxial compression in the temperature range of 233–393 K. In the stress vs. strain relationship, the orthorhombic Li3xLa1/3−xNbO3 (3x ≤ 0.06) clearly exhibits non-linear elastic hysteresis, whilst the tetragonal one (3x ≥ 0.12) shows a simple elastic behaviour. Ex-situ scanning electron microscopy observation on a polished surface before and after compression confirmed the martensitic reorientation of the domain structure of the orthorhombic Li3xLa1/3−xNbO3, which explains the observed non-linear hysteresis, whereas the domains of the tetragonal sample remain almost unchanged.

Dealloying-constructed hierarchical nanoporous bismuth-antimony anode for potassium ion batteries

Bi-Sb alloys are appealing anode materials for potassium ion batteries (PIBs) but challenged by their enormous volumetric variation during operation. Herein, a facile one-step dealloying protocol was devised and utilized to prepare the Bi-Sb alloys that manifest an exotic bicontinuous hierarchical nanoporous (np) microstructure ideal for volume-change mitigation and K+ transport percolation. The growth mechanism fostering the peculiar morphology of the np-(Bi,Sb) alloys was investigated and clarified via operando X-ray (XRD) and ex-situ scanning electron microscopy (SEM). In particular, the np-Bi6Sb2 electrode, optimized for comprehensive electrochemical performance, achieves decent reversible capacities and a superior lifespan, as benchmarked with the monometallic references and other Bi-Sb alloy electrodes. The (de)potassiation mechanism of the np-(Bi,Sb) alloys was studied by operando XRD and further rationalized by density functional theory (DFT) calculations, whereby a homogeneous (segregation-free) and robust two-step electrochemically-driven phase transformations’ catenation of (Bi,Sb) ↔ K(Bi,Sb)2 ↔ K3(Bi,Sb) was reliably established to substantiate the outstanding reversibility of the np-(Bi,Sb) anodes in PIBs.

Controlled lithium plating in three-dimensional hosts through nucleation overpotential regulation toward high-areal-capacity lithium metal anode

Three-dimensional (3D) porous hosts with abundant space inside can accommodate volume variation during lithium (Li) plating/stripping and promote reversibility of Li anode; however, the porous structure in 3D hosts usually induces uneven Li-ion/electron migration, giving rise to undesirable surface preferential Li nucleation and growth. A feasible coating strategy is developed herein to create gradient nucleation overpotentials on Cu mesh to realize the ‘bottom-up’ Li plating mode on 3D host. The ex-situ scanning electron microscopy (SEM) characterization confirms that this two-step coating strategy by coating Au and polymer blend (polyacrylonitrile and poly(vinylidene fluoride-co-hexafluoropropylene)) on the bottom and top sides of Cu mesh, respectively, successfully changes the nucleation overpotentials of this 3D host by altering Li affinity. As a result, stable Li plating/stripping and high coulombic efficiency of 97.3% can be achieved under high areal capacity of 5.0 mAh/cm2. The full cell using the modified Cu mesh with predeposited Li as the anode and lithium iron phosphate as the cathode (N/P ratio of ~4) can cycle steadily at 2.0 C with a capacity retention ratio of 96.4% after 150 cycles. The modification strategy proposed in this work is considered as a promising approach for designing a 3D conductive host for long-life and safe Li metal batteries.

Iron Contamination and Local Distribution within a 50 Cm Single-Channel Proton Exchange Membrane Water Electrolysis Cell

Proton exchange membrane water electrolysis (PEMWE) will play a major role in the clean and versatile energy conversion in the near future.[1] Offering scalable solutions of PEMWE are of high industrial interest and have to provide a sufficient durability and reliability.[2] To achieve this, a better understanding of the impact of contamination on the PEMWE performance is very crucial. In this context, the membrane electrode assembly (MEA) is susceptible to several degradation processes like metallic cations (Fe3+/2+ stemmed from tubing). In particular, soluble and reduced iron species forming by Fenton reaction might attack via radicals the MEA.[3,4] Hence, analyzing impurities and their resulting impacts on e.g. the proton transport resistance and degradation mechanisms at different length scales and local distributions are of large interest.In this work, the influence of spatially resolved iron contamination in MEAs on the cell performance has been investigated using a 50 cm single-channel PEMWE cell equipped with local current density measurement setup.[5] Adding defined amounts of FeSO4 via the anode inlet feed, the changes on the three main regimes of overpotentials, i.e. kinetic, ohmic and mass transport, is correlated with the current density mapping as well as local and global electrochemical impedance spectroscopy (EIS) measurements. Ex-situ scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to detect the distribution and agglomeration of iron species within the MEA.With this combined approach of electrochemical and ex-situ physical methods, the contamination pathways and their effects of (spatially resolved) iron contamination on the overall performance of MEA are investigated as a function of degree of contamination and operating conditions. Especially, the (spatially resolved) overpotential-specific degradation processes along the 0.5 m channel, which mimic a technically relevant stack size, allow us to conclude on the optimum design of MEA, targeting use of mitigation strategies and development of accelerated stress test protocols.[1] M.A. Pellow, C.J.M. Emmott, C.J. Barnhart, S.M. Benson, Energy Environ. Sci. 8 (2015) 1938-1952.[2] P.K. Shen, C.-Y. Wang, S.P. Jiang, X. Sun, J. Zhang, Electrochemical Energy: Advanced Materials and Technologies, CRC Press, 2015.[3] X. Wang, L. Zhang, G. Li, G. Zhang, Z.-G. Shao, B. Yi, Electrochim. Acta 158(2015) 253-257.[4] C. Rozain, P. Millet, Electrochim. Acta 131 (2014) 160e167.[5] C. Immerz, B. Bensmann, P. Trinke, M. Suermann, R. Hanke-Rauschenbach, JECS 165 (16) (2018)

Performance evaluation of an imidazoline corrosion inhibitor in a CO2-saturated environment with emphasis on localised corrosion

The ability of an imidazoline inhibitor to provide corrosion protection to X65 carbon steel in a CO2-saturated sodium chloride (NaCl) solution at 80ºC was evaluated. The performance of the inhibitor was investigated with respect to both generalised and localised corrosion behaviour using in-situ electrochemical measurements, ex-situ scanning electron microscopy (SEM) and non-contact surface profilometry. We demonstrate that the optimum inhibitor concentration required to minimise generalised corrosion is significantly lower than that required to minimise localised corrosion. This highlights the importance of systematic, post-test topographical measurements in the selection and optimisation of inhibitor dosage.

Plastic deformation mode and α/β slip transfer of Ti–5Al-2.5Cr-0.5Fe-4.5Mo–1Sn–2Zr–3Zn titanium alloy at room temperature

The plastic deformation mode and slip transfer between the α and β phases of Ti–5Al-2.5Cr-0.5Fe-4.5Mo–1Sn–2Zr–3Zn titanium alloy were investigated using a combination of ex-situ scanning electron microscopy tensile tests and electron backscatter diffraction characterization. With increasing tensile strain, local orientation changes (which lead to the sub-grain boundary generation and migration) occurred in the α phase, resulting in grain subdivision/coalescence. Afterward, the elongated α grains were subdivided (in general) into small equiaxed grains. Abrupt changes in the crystal orientation of the continuous β-matrix were, however, rare. Three primary slip systems (prismatic and basal slip: α phase and {110}<111> slip: β phase) accounted for more than 70% of the total slip system activity at each strain level. These systems could be activated with very low Schmid factors (<0.1) at high strains. The compatible deformation between the α and β phases was realized mainly through the slip transfer correlated with the three primary slip systems, and the prismatic slip system was the most active system. In general, the α phase underwent plastic deformation first and compelled plastic deformation of the separated β grains. Subsequently, the deformed β grains transmitted the strain between an adjacent α grain and other α grains, leading to deviations from the uniaxial stress state in the local region. This resulted in wide distributions of the activated slip systems with various Schmid factors, and considerable strain concentration and failure in the α phase near the phase boundaries.

Carbon Inverse Opals As a Sulfur Host for Advanced Lithium–Sulfur Batteries

Lithium Sulfur (Li–S) batteries are one of the most promising “beyond-lithium-ion” rechargeable battery systems in terms of both cost and specific energy density. (1, 2) Sulfur is one of the most abundant elements in the Earth’s crust and offers a high theoretical specific charge of 1672 mAh/g. (3) Furthermore, Li–S batteries can deliver a practical specific energy density of 400-600 Wh/kg, which is more than double the values offered by state-of-the-art lithium-ion batteries. (4, 5) However, issues related to the inherent insulating nature of S and the polysulfide shuttle continue to hinder the widespread commercialization of Li–S batteries. Consequently, there has been a significant research effort to identify S hosts that can assist in mitigating these limitations. Porous carbon materials have attracted a great deal of attention due to their excellent conductivity, high surface area and light weight. (6) Activated carbons and hollow carbon spheres (HCSs) have been shown to significantly improve the electrochemical performance of Li–S batteries in terms of specific capacity and its retention. (7-10) Inverse opal (IO) structured electrodes offer many potential benefits as a S host material. The spherical voids of an inverse opal can be filled with S and ensure good access of the electrolyte to the electrode surface. The carbon IOs may act as a highly ordered, three-dimensional, conductive scaffold to reduce lithium polysulfide dissolution into the electrolyte during cycling, thus reducing the effects of the detrimental polysulfide shuttle. Additionally, during discharge S is reduced to form Li2S and with prolonged cycling this process leads to structural instability of electrodes due to the large volume expansion (~80%) caused by S conversion into Li2S. The spherical pores of a carbon IO scaffold may constrain the volume expansion due to the formation of Li2S and therefore increase capacity retention. IOs and HCSs are typically synthesised using silica nanospheres, which require treatment in hydrofluoric acid or long-term exposure to highly basic solutions to etch away the hard template. (11, 12) In this work we detail the facile synthesis of carbon IO structured samples using polystyrene nanospheres, which are easily removed via thermal treatment, and their application as a S host material for Li–S batteries. We present a structural characterization of our carbon IO samples via analysis of Raman spectra, Fourier-transform infrared spectra and X-ray diffraction patterns. The electrochemical performance of the carbon IO S-hosts is evaluated via cyclic voltammetry, rate capability testing and long-term galvanostatic cycling tests. We demonstrate that our S infilled carbon IO cathodes are capable of delivering high specific charges with stable capacity retention, achieving a reversible capacity of ~ 750 mAh/g after the 100 cycles at a C/5 rate. The morphology of the carbon IOs after cycling will also be shown via ex-situ scanning electron microscopy. We demonstrate that by preparing a highly ordered, conductive, three dimensionally interconnected network in the form of a carbon IO and then infilling this porous scaffold with S, we can achieve specific charge values which are greater than standard S/C composite slurry electrodes.

Investigation of Olivine and Nasicon Structured Phosphates As Potential Cathode Materials for Magnesium Ion Batteries

The depletion of fossil fuel reserves as well as climate change motivate the development of new environmentally-friendly technologies for energy generation, storage, and consumption. Robust energy storage devices must be developed to meet the growing demand for portable electronics (i.e. laptops and mobile phones), electric vehicles and energy storage systems. Although lithium-ion batteries have mostly driven the revolution in modern electronics for the last three decades, new chemistries for “next-generation” batteries are currently under research and development. These new technologies are tasked with delivering better performance (capacity and current capability) at low cost while being environmentally friendly. In order to fill the gap between the current state of the art and future energy storage needs, magnesium is considered to be a possible alternative to lithium due to its natural abundancy and low toxicity. Furthermore, due to the divalent nature of the Mg2+ cations, a high theoretical volumetric capacity of 3833 mA h cm-3 can be attained if pure magnesium is used as the anode material.1 Additionally, since magnesium deposition takes place without dendrite formation on the Mg-metal anode surface, the Mg-cell is expected to be considerably safer than comparable cells based on lithium. Despite these positive attributes, the development of magnesium secondary batteries is hindered by the slow solid-state diffusion of Mg2+ ions into the cathode lattice. In this work, this issue is explored by synthesising and characterising two different phosphate-based systems to investigate their suitability as cathode materials for Mg-ion batteries, with phosphates chosen due to their structural stability and safety.2,3 The NASICON and olivine phosphates are known for their high conductivity in lithium-based systems and were selected here as potential hosts for Mg2+intercalation. NASICON compounds are usually reported as cathode or solid electrolyte materials for Li and Na-ion batteries, but there is a lack of reproducible data for Mg ion technologies. Therefore, the NASICON-structured Mg0.5Ti2(PO4)3 compound was selected for synthesis and further electrochemical characterisation. Additionally, the olivine-related (Mg0.5Ni0.5)3(PO4)2 was investigated as a novel cathode active material for the first time. This compound was chosen because of its open crystal structure, which is potentially favourable for magnesium ion diffusion. In parallel, V2O5 was used as a reference cathode active material in order to validate the electrochemical set-up, which is non-trivial for Mg chemistry. Mg0.5Ti2(PO4)3 and (Mg0.5Ni0.5)3(PO4)2 were obtained by the solid-state method and their crystal structures and phase purities were determined by Rietveld analysis of X-ray powder diffraction data. Scanning electron microscopy (SEM) was performed to analyse the particle morphologies, with particle sizes and porosities characterised by dynamic light scattering (DLS) and nitrogen adsorption (BET) techniques, respectively. Both cyclic voltammetry and galvanostatic cycling with potential limitation were carried out in order to investigate the insertion-extraction mechanism of Mg2+ ions. Ex-situ powder X-ray diffraction and SEM confirmed the crystal structures and particle morphologies, respectively, of the cathode active materials after cycling, while X-ray photon electron spectroscopy (XPS) was used to monitor changes in the oxidation state of the transition metal cation. Our results show that cells based on Mg metal anodes utilising Mg(ClO4)2 in acetonitrile as electrolyte suffer from the creation of a passivation layer leading to poor performance. In order to address this problem, activated carbon was used to replace metallic magnesium as the anode material, with the electrolyte acting as the main source for magnesium ions. The use of a carbon-based anode is seen to eliminate the passivation layer problem and improve capacity and cell cyclability. References H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci., 2013, 6, 2265–2279; P. Canepa, G. Sai Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. A. Persson, G. Ceder, Chem. Rev., 2017,117, 4287–4341; B. Kang, G. Ceder, Nature, 2009,458, 190.

The State of Electrodeposited Sn Nanopillars within Porous Anodic Alumina from in Situ X-ray Observations

Porous anodic alumina (PAA) can be used as a template for controlled electrodeposition and growth of nano-structures, it is also essential for long-lasting decorative coloring of aluminum. We have investigated the deposition of Sn nanopillars into PAA in-situ, with Grazing transmission small angle X-ray scattering, X-ray fluorescence and X-ray absorption near edge structure spectroscopy. An accumulation of Sn could be detected in the pores during the electrodeposition. From the X-ray absorption near edge structure spectroscopy measurements we could conclude that the deposited Sn was primarily in the metallic state. Ex-situ scanning electron microscopy cross-section measurements show Sn nanopillars inside the PAA.

Microarcing-enhanced tungsten nano and micro-particles formation in low pressure high-density plasma

In this article, tungsten dust formation kinetics in two distinct plasma regimes (glow and micro-arc-assisted glow discharge) are compared using the in situ time-resolved laser extinction method coupled to ex-situ Scanning Electron Microscopy analyses. This experimental study is carried out using low pressure/high density argon dual plasma that combines microwave and pulsed direct-current (tungsten cathode) discharges. Using this plasma system, we could access either to a sputtering glow regime (microarc-free) or to a micro-arcing assisted glow regime by tuning the direct-current voltage and the pulse frequency. On the one hand, in the sputtering glow regime, only dust nanoparticles with sizes ranging from 75 to 150 nm are produced with a low density of ∼1012 m−3. On the other hand, in the micro-arc-assisted glow regime, microparticles in the range of 1–5 μm are produced along with a strong enhancement of nanoparticle production with density up to ∼1014 m−3, and a broad size distribution ranging from ∼30 nm to 700 nm is observed. We show that micro-arcing not only results in micro-meter sized particles through melting/solidification but also strongly promotes the production of nanoparticles in the 100 nm size range.

Thixotropic gel electrolyte containing poly(ethylene glycol) with high zinc ion concentration for the secondary aqueous Zn/LiMn2O4 battery

We have designed an aqueous gel electrolyte containing fumed silica as the thixotropic gelling agent and poly(ethylene glycol) (MW=300g·mol−1) as the non-thixotropic gelling agent. Poly(ethylene glycol) is also the dendrite suppressor and the corrosion inhibitor. Both PEG300 and fumed silica can inhibit dendrite formation, shown by chronoamperometry results and ex-situ scanning electron microscopy images. Furthermore, the corrosion current density on the Zn anode in the 4wt%FS-1wt%PEG300 gel electrolyte is 27% less than that of the Zn in the reference aqueous electrolyte. Secondary Zn/LiMn2O4 batteries using the 4wt%FS-1wt%PEG300 gel electrolyte exhibit higher cyclability (12% and 39% higher capacity retention, after 300 and 1000cycles, in Swagelok and large cells, respectively) than those using the reference aqueous electrolyte. The vast improvements in cycling performance, reliability, and higher resistance to premature failure makes the PEG-FS gel a much better alternative to liquid electrolytes for maintenance-free energy storage applications.

In-situ nitrogen-doped hierarchical porous hollow carbon spheres anchored with iridium nanoparticles as efficient cathode catalysts for reversible lithium-oxygen batteries

One of the biggest challenges on the way to the commercialization of lithium-oxygen (Li-O2) batteries (LOBs) is the exploration of an air electrode with high electronic conductivity, steadily porous architecture, and high-efficiency bifunctional catalytic activity. In this study, nitrogen-doped and iridium decorated carbon spheres with hollow and hierarchical porous structure were successfully fabricated and used as excellent bifunctional electrocatalysts in alkaline aqueous environment as well as in non-aqueous LOBs. This material structure with large pore volume and high specific surface area provides sufficient room and numerous active sites for the deposition of Li2O2 product. Moreover, the in-situ nitrogen doping further enhances the electron conductivity as well as the electrocatalytic activity toward oxygen, yielding a gratifying discharge platform potential of 2.77 V, and a high discharge capacity (6849 mAh g−1). After anchoring with Ir nanoparticles, the resulting composite material presented significantly reduced charge overpotential (0.83 V) and improved reversibility. Meanwhile, owing to the synergistic effect among the porous carbon, nitrogen heteroatom, and Ir nanocrystals, the increased discharge capacity of 8239 mAh g−1 and high discharge plateau of 2.80 V were also achieved. Besides, the excellent stability of the recharged air-cathode architecture was confirmed via ex-situ scanning electron microscopy.

Metal organic frameworks derived cobalt sulfide/reduced graphene oxide composites with fast reaction kinetic and excellent structural stability for sodium storage

We report a metal-organic framework-derived Co9S8 nanoflakes on reduced graphene oxide sheet composites as an advanced sodium-ion battery anode. Using a galvanostatic intermittent titration technique, we reveal that the sodium diffusion coefficient of the composite is higher than that of its counterpart. Ex-situ scanning electron microscopy images suggest the excellent mechanical stability of Co9S8 nanoflakes on the reduced graphene oxide sheet electrode during cycling, thereby facilitating cyclic stability. The partial surface-induced capacitive effect also contributes to electrochemical performance. With the reduced graphene oxide, the Co9S8 nanoflakes on the reduced graphene oxide sheet electrode deliver a high discharge capacity of 551 mA h g−1 at 0.1 A g−1, a good rate capability at 10 A g−1, and an excellent cyclic stability up to 500 cycles. rGO/Co9S8 shows potential for practical applications in Na3V2(PO4)3‖rGO/Co9S8 full cells.

(Invited) Rational Design of Nanoporous Polymer Electrolytes and Solid-Liquid Interphases for Lithium Metal Batteries

Advances in the basic science and engineering principles of electrochemical energy storage is imperative for significant progress in portable electronic devices. In this regard, metal based batteries comprising of a reactive metal (like Li, Na, Al) as anode have attracted remarkable attention due to their promise of improving the anode-specific capacity by as much as 10-fold, compared to the current state-of-art Li-ion battery that uses a graphitic anode. Perhaps their greatest advantage lies in the possibility of using of a Li-free high-capacity cathode like Oxygen that can improve the gravimetric energy density of batteries from ~0.3kWh/kg to ~12kWh/kg (i.e. comparable to the useful energy available from combustion of hydrocarbons). A persistent challenge with batteries based on metallic anodes, concerns their propensity to fail by short-circuits produced by dendrite growth during battery recharge, as well as by runaway of the cell resistance due to internal side reactions with liquid electrolytes. In this talk, I will discuss my research that utilizes multiscale transport modeling and experiments to fundamentally understand and to thereby develop rational designs for polymer electrolytes and electrode-electrolyte interphases that overcome these challenges (Tikekar, Choudhury et al. Nat. Energy 2016). There have been several studies in literature dedicated to the prevention of dendrite growth by means of a high modulus physical barrier. However, electrolytes/separators with high mechanical strength tend to have low ionic conductivity, thus limiting their practical use. A recent theoretical study from our group reported a linear stability analysis of dendrite growth (Tikekar et al., Sci Adv. 2016) of metal electrodeposition and showed that the length-scale on which transport occurs near the electrodes could be as important as electrolyte modulus in stabilizing metals against dendrite formation. In a nutshell, this study concluded that dendrites can be prevented from crossing over to the counter electrode using battery separators with pore-diameter lower than critical (smallest) size of the dendritic nucleate. To evaluate this proposal, we designed cross-linked nanoparticle-polymer composite electrolytes with tunable pore size and quantified the stability of metal electrodeposition in these systems. In contrast to most previously reported polymer electrolytes, the crosslinked membrane simultaneously showed good mechanical strength (~1MPa) and high ionic conductivity at room temperature (~5mS/cm), which is a consequence of the high crosslinking node points in these membranes (Choudhury et al. Nat. Commn. 2015). Direct visualization experiments were performed to understand the effect of pore-size on dendrite growth, which showed remarkable agreement with the theoretical predictions. Furthermore, when operated in a battery, the crosslinked membrane showed the highest short circuit time compared to similar electrolytes reported in the literature. Importantly, these studies showed that while the tendency for battery failure by dendrite-induced short-circuits can be reduced in polymer electrolytes, the issue of capacity-fading as a result of continuous reactions of the metal with liquid electrolyte persists. An additional striking fact in the electrodeposition literature not addressed by the linear stability analysis is that certain metals, including Magnesium, do not form dendrites. In the second part of my talk, I will show how multiscale analysis of transport at electrochemical interfaces enables design of stable solid-liquid interphases for reactive metal batteries. Recently, we used Density Functional Theory (DFT) calculations to quantify the diffusion energy barrier of ions on Mg, Li, Na surfaces and interestingly it seen that the diffusion barrier of Mg (0.02eV/atom) is several fold lower than Li (0.14eV/atom) or Na (0.16eV/atom) metals. In fact, the diffusion barrier of Li2CO3, Li2O (the commonly found compounds in lithium interface) is even higher, which is consistent with the dendritic electrodeposition in such batteries. However, in quest for finding stable interfaces, we observed that most metal halides (LiF, LiBr, NaF etc.) have much lower diffusion barrier. In other words, halide-rich interfaces on lithium or sodium can lead to stable electrodeposition similar to Mg deposition (Choudhury et al. Nat. Commn. 2017). We further utilize Classical Nucleation Theory (CNT) to understand implication of the ab-initio model in macroscopic metal deposition. The predictions from the coupled DFT-CNT model were validated using ex-situ scanning electron microscopy as well as in-situ optical microscopy. The nucleation pattern, indeed, showed a strike difference between usual (carbonate-rich) and halide-rich lithium interfaces. Based on these fundamental understanding, the solid electrolyte interphase in lithium metal batteries were artificially modified using organo-metallic reactions to enable enhanced reversibility in high energy density Lithium-Oxygen battery that demonstrated extended capacity retention and longer cycle life (Choudhury et al. Sci. Adv. 2017). Figure 1

Controlling the sustainability and shape change of the zinc anode in rechargeable aqueous Zn/LiMn2O4 battery

The use of thixotropic gel electrolytes in the rechargeable hybrid aqueous battery improves the battery performance but it is required to have a corrosion inhibitor in the gel electrolyte. These inhibitors are not always friendly to the environment. In this work, we use lignin – a renewable material – to neutralize strong acid sites of the fumed silica gelling agent prior to gel preparation. Linear polarization, chronoamperometry, and ex-situ scanning electron microscopy examinations show that the new gel electrolyte reduces the corrosion on zinc (up to 43%) and supports planar zinc deposit. In other words, the shape of the zinc surface is controlled and it is further confirmed by the XRD and SEM of post-battery run anodes. Moreover, the battery using this new lignin coated fumed silica based gel electrolyte exhibits a float charge current as low as 0.0025 mA after 24 h of monitoring, which is 30.6% lower than the reference. The capacity retention of gelled battery is as high as 82% after 1000 cycles at 4 C, which is 14% higher than the reference battery using reference liquid electrolyte under the same CC-CV test, complemented by lower self-discharge and higher rate capability. The results lead the team nearer to a commercializable gelled battery system.

A super-long life rechargeable aluminum battery

High energy and power density rechargeable batteries with low cost, long cycle life and high safety remain a great demand of portable electronics and grid storage systems. Recently, rechargeable aluminum batteries (RABs) have attracted much attention owing to its high volumetric capacity (8046 mAh cm−3), low cost and ultra-safety. However, harsh reaction conditions and complicated processes are usually used in preparation of electrode materials, hindering the practical application. Herein, a commercial ordered mesoporous carbon (CMK-3) as a cathode for RABs is proposed, which shows a super-long life of >36,000 charge/discharge cycles with a high coulombic efficiency of >97% and excellent rate performance up to 3000 mA g−1. Moreover, The Al/CMK-3 battery has a high energy density of ~45 Wh kg−1. Last, the structure changes and (de)intercalation of chloroaluminate anions into the mesopores of CMK-3 during the charge/discharge process were checked by ex-situ scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman and X-ray photo spectroscopy (XPS). Commercially availability and affordable cost of the cathode material make Al/CMK-3 battery more promising for wearable and portable appliances.

Sustainable gel electrolyte containing Pb2+ as corrosion inhibitor and dendrite suppressor for the zinc anode in the rechargeable hybrid aqueous battery

Dendrite formation and corrosion are two major problems occurring on the zinc electrode of the rechargeable hybrid aqueous battery (ReHAB). In this work, we have designed a gel electrolyte containing fumed silica (FS) as the gelling agent and Pb2+ as the dendrite suppressor and also the corrosion inhibitor in aqueous liquid media. Both Pb2+ and fumed silica can inhibit dendrite formation, evidenced by chronoamperometry results and ex-situ scanning electron microscopy images. Furthermore, linear polarization results reveal that corrosion current density on the Zn anode when in contact with the PbSO4 doped 5%FS gel electrolyte is 20% smaller than that of the Zn when in contact with the reference aqueous electrolyte. The ReHAB using the Pb2+ containing gel electrolyte exhibits higher cyclability (75% capacity retention after 300 cycles at 1 C rate) than the ReHAB using the reference aqueous electrolyte (60% capacity retention at the same condition). Self-discharge is massively reduced, represented by an 18% smaller loss of open-circuit voltage after monitoring for 24 h. Float charge current density is reduced significantly up to 35% after 24-h of constant charging the batteries at 2.1 V vs. Zn2+/Zn. The results suggest that battery performance improves when both corrosion current density and dendrite formation are suppressed.

Investigation of Passive Layers Formed on Alloy 600 in Zinc Containing High Temperature Primary Water

Nickel-based Cr-Fe alloys have been found to show very low corrosion rates in extreme environments and thus have been extensively used in industries, such as in nuclear power plants. One of the reasons that Ni-Cr-Fe alloys show good corrosion resistance is that there are oxides that prevent the bare metal from general corrosion. However, Pressurized Water Reactors (PWRs) have experienced stress corrosion cracking (SCC) on the primary side of the Alloy 600 (Ni-15Cr-9Fe) steam generator tubing. It is believed that passive layer formed on Alloy 600 is crucial for SCC initiation. Zn ions are added to primary water in industry in order to reduce SCC initiation. However, the mechanism of SCC suppression with Zn is not yet fully understood. The Zn incorporation process is of great importance in the way that it can help understand the mechanism of SCC initiation. Our research aims to understand the influence of surface oxides of Alloy 600 on SCC in primary water of PWR, focusing on the effect of Zn ions during short period of time (less than 100 hours) at different potentials. The present research examined the effect of Zn ions on the passive layer using in-situ electrochemical method as well as ex-situ characterization method. We constructed a system simulating the high temperature primary water with 100ppb Zn addition and operated the system at 320 C and 1800psi. The sample was oxidized in the autoclave for up to 48 hours at different potentials. During the oxidation period, electrochemical impedance spectroscopy (EIS) was applied at different oxide forming potentials in order to get information of how the alloy performs at different potentials. Ex-situscanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron dispersive spectroscopy (EDS) were also performed on the samples to determine the morphology and chemical profiles of the passive layer. Our EIS study indicated that there was likely a change in oxide property on Alloy 600, likely related to the incorporation of Zn ion, at different potentials for short time oxidation. It was found from the ex-situ experiments that with potential changes, both the thickness and the morphology of the passive layer changes, which agreed with the changes in the impedance results. Figure 1 shows the changes on surface morphology on Alloy 600 samples polarized at different potentials for up to 40 hours. It is indicated that both the distribution and the size of oxide particles changes with polarizing potentials. Zn was found to incorporate into the passive layer of the oxide, substituting some of the Ni content in the passive layer. As potential increased, the content of Zn incorporation changed. Figure 1