Aqueous Li-air Batteries Research Articles

Recent progresses and challenges in aqueous lithium-air batteries relating to the solid electrolyte separator: A mini-review.

The lithium–air (Li–air) battery utilizes infinite oxygen in the air to store or release energy through a semi-open cathode structure and bears an ultra-high theoretical energy density of more than 1,000 Wh/kg. Therefore, it has been denoted as the candidate for next-generation energy storage in versatile fields such as electric vehicles, telecommunications, and special power supply. Among all types of Li–air batteries, an aqueous Li–air battery bears the advantages of a high theoretical energy density of more than 1,700 Wh/kg and does not have the critical pure oxygen atmosphere issues in a non-aqueous lithium–air battery system, which is more promising for the actual application. To date, great achievements have been made in materials’ design and cell configurations, but critical challenges still remain in the field of the solid electrolyte separator, its related lithium stripping/plating at the lithium anode, and catholyte design. In this mini-review, we summarized recent progress related to the solid electrolyte in aqueous Li–air batteries focusing on both material and battery device development. Moreover, we proposed a discussion and unique outlook on improving solid electrolyte compatibility and battery performance, thus designing an aqueous Li–air battery with higher energy density and better cycle performance in the future.

Synergistic bifunctional catalytic effect at metal oxide-based catalyst for oxygen electrodes: influence of support and investigation in DMSO

Li-air batteries are one of the most promising candidates for rechargeable systems.[1] Within the context of elucidating the possibilities of aqueous Li-air batteries, developing a cost-effective bifunctional catalyst for oxygen reactions is a key issue. Metal oxides including spinels and perovskites have been shown as efficient catalysts for OER,[2] while Ag is known as a good catalyst for ORR. We have recently shown that a mixture of Ag particles with Co3O4 nanoparticles has superior bifunctional activity than its own components.[3] Here, we will demonstrate that such effect can also be observed when other support materials than Ag are used. Therefore, this effect could partially be due to a conductivity effect. However, experiments using smooth electrodes suggest that there is a synergistic effect. We will further demonstrate that this effect is also observed for various perovskites loaded on Ag. XPS analysis has shown that the presence of Ag+ in contact with Co3O4 facilitates the redox switching of Co3O4, which might be the reason for the enhanced catalytic activity of the mixture.[4] Moreover, the mechanism underlying OER on Co3O4 and mixed Ag+Co3O4 catalysts is further studied using differential electrochemical mass spectrometry together with 18O-isotope labelling experiments.[4-5] The results revealed that the lattice oxygen of the oxide takes part in OER and that the amount of oxygen exchange on the mixed catalyst is larger than that on Co3O4. The active surface area is also estimated from these measurements and is compared to that obtained from a simple ball model and BET data.[6] Investigation of the catalytic activity of Co3O4 catalyst towards oxygen reactions in aprotic electrolytes, namely DMSO, is also presented. Literature: [1] K. M. Abraham, Z. Jiang, J. Electrochem. Soc. 1996, 143, 1-5. [2] A. Bergmann, E. Martinez-Moreno, D. Teschner, P. Chernev, M. Gliech, J. F. de Araújo, T. Reier, H. Dau, P. Strasser, Nature Communications 2015, 6, 8625. [3] H. M. A. Amin, H. Baltruschat, D. Wittmaier, K. A. Friedrich, Electrochim. Acta 2015, 151, 332-339. [4] H. Amin, C. J. Bondue, S. Eswara, U. Kaiser, H. Baltruschat, Electrocatalysis 2017, 8, 540-553. [5] S. Fierro, T. Nagel, H. Baltruschat, C. Comninellis, Electrochem. Commun. 2007, 9, 1969-1974. [6] H. M. A. Amin, H. Baltruschat, Phys. Chem. Chem. Phys. 2017, 19, 25527-25536.

Hybrid Li Ion Conducting Membrane as Protection for the Li Anode in an Aqueous Li-Air Battery: Coupling Sol-Gel Chemistry and Electrospinning.

Aqueous lithium-air batteries have very high theoretical energy densities, which potentially makes this technology very interesting for energy storage in electric mobility applications. However, the aqueous electrolyte requires the use of a watertight layer to protect the lithium metal, typically a thick NASICON glass-ceramic layer, which adds ohmic resistance and penalizes performance. This article deals with the replacement of this ceramic electrolyte by a hybrid organic-inorganic membrane. This new membrane combines an ionically conducting inorganic phase for Li ion transport (Li1.3Al0.3Ti1.7(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer for water tightness and mechanical properties. The Li ion transport through the membrane is ensured by an interconnected 3-D network of crystalline LATP fibers obtained by coupling an electrospinning process with the sol-gel synthesis followed by thermal treatment. After an impregnation step with PVDF-HFP, hybrid membranes with different volumetric fractions of PVDF-HFP were synthesized. These membranes are watertight and have Li ion conductivities ranging from 10-5 to 10-4 mS/cm. The conductivity depends on the PVDF-HFP volume fraction and the fibers' alignment in the membrane thickness, which in turn can be tuned by adjusting the water content in the electrospinning chamber during the process. The alignment of fibers parallel to the membrane surface is conductive to poor conductivity values whereas a disordered fiber mat leads to interesting conductivity values (1 × 10-4 mS/cm) at ambient temperature.

Molten salt synthesis and characterization of fast ion conductor Li6.75La3Zr1.75Ta0.25O12

The limited electrochemical stability and the flammability of the liquid electrolytes presently used in Li-ion batteries stimulates the search for alternatives including ceramic solid electrolytes. Moreover, solid electrolytes also fulfil crucial functions in various large-scale energy storage systems, e.g. as anode-protecting membranes in aqueous Li-air batteries. Here, the processing of the solid electrolytes Li7La3Zr2O12 is studied for applications in Li-air batteries. Molten salt method (MSM) was adopted previously on synthesis of simple oxides; to the best of our knowledge, we report for the first time the adaptation of the MSM to prepare this class of solid electrolytes. As a model compound, we prepared the garnet-related Li6.75La3Zr1.75Ta0.25O12. It has been prepared by using stoichiometric amounts of La2O3, ZrCl4, and Ta2O5 in excess 0.88 M LiNO3:0.12 M LiCl molten salt. Subsequently, samples were heated to various temperatures in the range 600–900 °C for 6 h in air in a recrystallized alumina crucible and finally washed with distilled water to remove excess salts. The obtained Li6.75La3Zr1.75Ta0.25O12 electrolyte powder was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman, and impedance spectroscopy as well as surface area measurements. The cubic single phase was obtained for samples prepared at temperatures ≥700 °C. The effects of washing with water or aqueous LiOH solution on the structure and conductivity of the phases will be discussed.

Carbon Based Phthalocyanines As Electrocatalysts for Li Air Batteries

Li-air batteries are appealing as they offer much higher energy density than the current Li-ion batteries. However, the non–aqueous Li-air batteries suffer from poor cycle life due to electrolyte decomposition and clogging of the air electrode by insoluble discharge products. Efficient bifunctional catalysts could lower the overpotential and improve the stability of Li-air batteries, thus prolonging its cycle life. This study focuses on Iron phthalocyanines (FePc) supported on carbon materials as a solid electrocatalyst for lithium air batteries. Metal phthalocyanines were utilized mainly because of their structural analogy which could be fine- tuned by the metal being used, accessibility, and low cost. The carbon supports such as reduced graphene oxide (rGO) and carbon nanotubes (CNT) were utilized which rendered desirable surface properties like high surface area and high electronic conductivity. FePc/carbons delivered superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable and better than that of commercial Pt/C. The bifunctional catalysts were then applied as electrocatalysts in non-aqueous lithium air batteries. The air cells delivered better electrochemical performance mainly by reducing the large overpotential associated with ORR and OER. The cells exhibited better reversibility and cyclability as well. The improved electrocatalytic activity was mainly because of the π–π interaction between carbons and iron phthalocyanines. In addition, the effects of ball milling by ball milling the FePc, and the effects of nitrogen (N2) doping by doping the carbon supports with N2 were investigated. Ball milling has significantly improved the electrocatalytic properties of FePc and N2 doping further enhanced the overall performance.

Investigation on lithium ion conductivity and structural stability of yttrium-substituted Li7La3Zr2O12

Advanced Li-air battery architecture demands a high Li+ conductive solid electrolyte membrane that is electrochemically stable against metallic lithium and aqueous electrolyte. In this work, an investigation has been carried out on the microstructure, Li+ conduction behaviour and structural stability of Li7La3-xYxZr2O12 (x = 0.125, 0.25 and 0.50) prepared by conventional solid-state reaction technique. The phase analysis of Li7La3-xYxZr2O12 (x = 0.125, 0.25 and 0.50) sintered at 1200 °C by powder X-ray diffraction (PXRD) and Raman confirms the formation of high Li+ conductive cubic phase (\( Ia\overline{3}d \)) lithium garnets. Among the investigated lithium garnets, Li7La2.75Y0.25Zr2O12 sintered at 1200 °C exhibits a maximized room temperature total (bulk + grain boundary) Li+ conductivity of 3.21 × 10−4 S cm−1 along with improved relative density of 96 %. The preliminary investigation on the structural stability of Li7La2.75Y0.25Zr2O12 in the solutions of 1 M LiCl, dist. H2O and 1 M LiOH at 30 °C/50 °C indicates that the Li7La2.75Y0.25Zr2O12 is relatively stable against 1 M LiCl and dist. H2O. Further electrochemical investigation is essential for practical application of Li7La2.75Y0.25Zr2O12 as protective solid electrolyte membrane in aqueous Li-air battery.

Facile synthesis of Fe@Fe2O3 core-shell nanowires as O2 electrode for high-energy Li-O2 batteries

Fe@Fe2O3 core-shell nanowires were synthesized via the reduction of Fe3+ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe2O3 shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O2 batteries with the charge voltage plateau reduced to ∼3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g−1. The excellent electrochemical properties of Fe@Fe2O3 as an O2 electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O2 batteries.

N-Co-O Triply Doped Highly Crystalline Porous Carbon: An Acid-Proof Nonprecious Metal Oxygen Evolution Catalyst.

In comparison with nonaqueous Li-air batteries, aqueous Li-air batteries are kinetically more facile and there is more variety of non-noble metal catalysts available for oxygen electrocatalysis, especially in alkaline solution. The alkaline battery environment is however vulnerable to electrolyte carbonation by atmospheric CO2 resulting in capacity loss over time. The acid aqueous solution is immune to carbonation but is limited by the lack of effective non-noble metal catalysts for the oxygen evolution reaction (OER). This is contrary to the oxygen reduction reaction (ORR) in acid solution where a few good candidates exist. We report here the development of a N-Co-O triply doped carbon catalyst with substantial OER activity in acid solution by the thermal codecomposition of polyaniline, cobalt salt and cyanamide in nitrogen. Cyanamide and the type of cobalt precursor salt were found to determine the structure, crystallinity, surface area, extent of Co doping and consequently the OER activity of the final carbon catalyst in acid solution. We have also put forward some hypotheses about the active sites that may be useful for guiding further work.

Stability of garnet-type solid electrolyte LixLa3A2 -yByO12 (A = Nb or Ta, B = Sc or Zr)

Garnet-type solid electrolytes LixLa3A2-yByO12 (A=Nb5+ or Ta5+, B=Sc3+ or Zr4+) were examined with respect to their stability in contact with lithium metal, water, and a liquid electrolyte for application in an aqueous lithium-air secondary battery. Electrolyte samples were synthesized by a solid state reaction method using a magnesia rather than alumina crucible to avoid aluminum contamination. The garnet-type electrolytes including Zr4+ ions exhibited higher ionic conductivity than those with Sc3+ ions. The electrolytes including Ta5+ were stable in contact with lithium metal, whereas those with Nb5+ were not. Lithium ions in all the samples were partly proton-exchanged in distilled water; however, the garnet-like structure remained unchanged as reported in many papers. In contrast, all the electrolyte samples were stable in the aqueous solution of 10M LiCl and 2M LiOH (suitable electrolyte for aqueous Li-air battery system). The garnet-type lithium ion conductors comprising Zr4+ and Ta5+ ions were revealed to be suitable for use as the protective membrane between the lithium metal electrode and aqueous electrolyte in rechargeable lithium-air batteries.

The Efficiency and Mechanism of 3D-Ordered Macroporous La0.6Sr0.4Co0.2Fe0.8O3 as an Electrocatalyst for Aprotic Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries with high energy density have thought to be the most attractive alternatives to nowadays Li-ion batteries. However, some challenges are still to be resolved, among which is the high charge overpotential that could compromise the cycle stability and capacity performance. [1, 2] The high overpotential is ascribed to the insolated discharge products Li2O2, which could not decompose completely during the charge processes. With the increasing cycles of battery tests, the Li2O2 will crystallize and block the porous cathode materials. [3, 4] However, recent studies have demonstrated that the structure and morphology could influence the conductivity and thus affect the overpotential. It is crucial to find an electrocatalyst that could accelerate the decomposition of Li2O2 and influence the crystallization of Li2O2 to get small size or amorphous Li2O2 products. [5, 6] Perovskite oxides La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) have been proved efficient to lower overpotential in aqueous Li-air batteries [7] but not have been applied in Li-O2 batteries. Herein the 3D-ordered macroporous LSCF (3D-LSCF) with very high BET surface area have been prepared and employed as electrocatalyst in Li-O2 batteries with DMSO based electrolyte. The Li-O2 batteries with this catalyst show lower overpotential, better cycle stability and capacity performance. As shown in Figure 1, the charge plateau of Li-O2 batteries with 3D-LSCF catalyst are flat and the charge potential is below 3.8V after nine cycles. The primary reason of the lower overpotential may be ascribe to the high oxygen pathways in 3D-LSCF structure which could accelerate the decomposition of Li2O2 products. [8] In order to conform the better ability of oxygen transmit of 3D-LSCF, the batteries have been tested in different levels of oxygen environments. With the increase of oxygen content, the performance of batteries without catalyst has increased more obviously than with 3D-LSCF catalyst, which indicates that the 3D-LSCF catalyst could transmit relatively sufficient oxygen. The morphologies of pure KB electrode and KB/3D-LSCF electrode at different states have been observed and the 3D-ordered macroporous structure of LSCF is beneficial to form small size of Li2O2 with large contact area to the KB that could assist in the decomposition at lower charge potential. The details of results and specific analysis will be exhibited in the presentation. Fig. 1 The cycle performance of Li-O2 batteries with 3D-LSCF catalyst at the current densities of 100mAg-1. Acknowledgements: This program was supported by Innovative Research Team in University (PCSIRT No. IRT1014).

Elaboration and Characterization of Flexible Li+ Conducting Membranes for Aqueous Li-Air Batteries

Summary: Lithium-air batteries have attracted a lot of research interest recently because they can close the gap between the electric vehicle and the internal combustion engine vehicle. Several challenges remain before making this technology fully functional, but using an aqueous electrolyte addresses several of them. However, it requires the use of a protected lithium anode. While the state of the art is using a fragile glass-ceramic membrane, we propose here to develop a ceramic/polymer hybrid membrane, combining water-tightness, flexibility and Li+ conduction. Introduction Massive use of electric vehicles needs a real breakthrough in battery technologies, to simultaneously increase the specific energy and decrease the costs. Several systems are studied, including lithium sulfur, zinc air and especially lithium-air. In lithium-air, the capacity of the negative electrode is no longer limited by the positive electrode: the latter harvests its reactant, oxygen, directly from the environment at discharge and releases it during charge. Specific energy is then drastically increased. However, this promising technology is still at the laboratory scale, and several challenges remain to be addressed. Aqueous based lithium-air [1,2] presents several advantages, but requires the use of a protected lithium anode [3], i.e, a solid Li+ ionic conductor is used to isolate the metallic lithium from the aqueous electrolyte. However, the integration of glass-ceramic makes the system more fragile, limits its cyclability and increases ohmic resistance. We propose here a different approach to protect the lithium electrode. It consists in producing a hybrid membrane [4] which combines watertightness, flexibility and Li+ ion conductivity. This membrane is made from an Li+ conducting inorganic nanofiber mat, embedded in watertight polymer. Experimental The critical step for producing this hybrid membrane is the synthesis of the nanofibers mat through electrospinning. This versatile process involves an electric field to break the surface tension of a liquid, to extrude it into a solid fiber [5]. Originally designed for polymers, it has been less explored for ceramic inorganic materials [6]. A solution containing both a supporting polymer and inorganic precursors is injected in an electric field to yield hybrid nanofibers. These fibers are then thermally treated to decompose the organic binder and crystallize the lithium-conducting ceramic phase as shown in figure 1. The inorganic fibers are then impregnated with a polymer to obtain final mechanical resistance and water tightness. Materials were characterized at every steps of this process: electrospun hybrid nanofibers, inorganic crystalline nanofibers, and nanofiber mat embedded in polymer which is the final membrane. The techniques used were scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and impedance spectroscopy. Results A new sol-gel synthesis was successfully developed to meet the requirements of electrospinning, for both the perovskite Li3xLa2/3-xTiO3 and the NASICON structure Li1+xAlxTi2-x(PO4)3. Pure ceramic nanofibers were obtained for both compositions. Impregnation was then optimized to reach the desired properties. Watertight and Li+ conducting membranes were achieved. Conductivities up to 2.10-6 S.cm-1 were obtained. The performances of the various membranes were discussed as a function of processing parameters, including environmental conditions and organic to inorganic ratio. These membranes were then tested in half cells as a solid electrolyte. Conclusion A flexible hybrid solid state membrane was developed for aqueous Lithium-air batteries. The inorganic crystalline nanofiber mats were obtained by electrospinning followed by a thermal treatment. These mats were then embedded in a polymer to ensure water tightness. The final membranes are flexible, water tight and Li+ ions conducting. Fibers availability at the surface and organic/inorganic ratio still have to be improved to enhance ionic conductivity. Acknowledgements The authors would like to thank Domitille Giaume (IRCP) for the ICP-MS analysis.

Lagp-Based Composite Membrane for Rechargeable Aqueous Li-Air Battery

Novel high efficiency grid-scale high energy density storage systems, such as rechargeable Li-air batteries (LABs), are urgently needed to enable and manage a more wide-spread utilization of renewable energy sources. Among these organic electrolyte LABs offer the highest gravimetric energy density, but they suffer from limited cyclability and poor energy efficiency due to the high over-potential during charge and discharge. LABs relying on aqueous catholytes promise somewhat lower theoretical capacity but a higher potential to reach theoretical limits in practical devices. In these systems catholytes with high solubility for the discharge product enhance the cycle efficiency and power performance. The fast ion-conducting electrolyte membrane is the key component of an aqueous Li-air battery, as it protects the lithium anode from reacting chemically with the catholyte solution. Here, an inorganic-organic hybrid membrane based on NASICON-type Li1.5Al0.5Ge1.5(PO4)3 (LAGP) ceramics and PEO:PVDF:LiBF4 with a thickness of 100-150 μm is designed and tested inside an aqueous LAB. By varying the mass fraction of the ceramic and polymer constituents mechanical properties and ionic conductivity of the membrane were optimized yielding conductivities of 5×10-4 S cm-1. The membrane in an Li-air cell also has to be stable in contact with the lithium anode. Cyclic voltammetry of the membrane up to 4 V vs. Li/Li+shows only two distinct peaks of cathodic deposition and anodic dissolution of the anode, confirming the wide electrochemical window of the membrane. To identify a suitable solid electrolyte:catholye couple, the membrane was immersed in an aqueous solution of LiCl (10M) and the changes in the structure and conductivity were monitored. Geometry and XRD pattern of the membrane are almost identical before and after immersion for 20 days, while the conductivity of the membrane increases with immersion time. Figure 1 demonstrates the schematic design of the cell. Hybrid inorganic-organic membrane is placed between lithium anode and catholyte in the reaction chamber (cell). The catholyte is circulated between the cell and a reservoir. The air cathode consists of finely dispersed Pt on multi-walled carbon nanotube arrays on a carbon fiber cloth, so that oxygen reduction and formation are effectively catalyzed. Room temperature charge/discharge profiles of a cell cycled in the voltage range of 1.5 to 4.5 V for the first 10 cycles are shown in Figure 2. The cell is operated with a constant current density of 0.5 mAcm-2. Both charge and discharge cycles are limited to one hour. During the first cycle, the cell shows charge and discharge plateaus at 4.0 V and 2.6 V, respectively. The equilibrium potential is considerably increased compared to cells without a continuous supply of the catholyte; all other components remaining the same. To further enhance the energy efficiency of the LAB we explore ways to reduce the internal cell resistance by optimizing membrane thickness and patterning, as well as by tailoring charge transfer processes at the electrode:electrolyte:catholyte interfaces. Figure 1

Nafion Coated Lithium Ion Conducting Ceramic for Aqueous Li-Air Batteries

Protected lithium anodes use a lithium ion conducting ceramic membrane to separate the anode side and the cathode side, making it possible to use aqueous catholytes in a Li-air battery. However, this ceramic membrane is not chemically stable in acidic or alkaline electrolyte solutions. In order to extend the operational life of this protecting ceramic, modifications of its surface are needed. In this work, we coat the ceramic membrane with a thin layer of lithiated Nafion. Nafion coatings were obtained by using a doctor-blade method, with a typical thickness in the range of 6 to 10 μm. Electrochemical impedance spectroscopy showed that the Nafion coatings lead to a small increase in the membrane resistance. The coated ceramic showed better capacity and stability in cell performance when tested in extended discharge.

Are Oxide Electrolytes Moisture Insensitive? Effect of Corrosion at the Grain Surface of Li3xLa2/3-XTiO3 Inhibiting Li-Ion Transport

Introduction Solid state electrolytes presenting high lithium ions mobility are of great challenge to improve safety and durability of secondary Li-ions batteries. Among the solid electrolytes, lithium lanthanum titanates and related compounds have attracted much attention due to their remarkably fast lithium conduction in bulk (up to 1 mS/cm at RT [1]) and have successfully been used as separator in an aqueous Li-air battery cell [2]. The processing and stability of these materials in air present a great advantage simplifying the production process and hence the production costs. Unfortunately Li3xLa2/3-xTiO3presents a high grain boundary resistivity and low densification properties decreasing the total conductivity to values lower than 0.01 mS/cm. To date no complete study has clearly explained the origin of the high grain boundary resistivity. In this work, we identify and solve the high grain boundary issue by changing the processing conditions for ceramic samples. Experiments Pure compounds corresponding to the stoichiometry Li0.34La0.55TiO3 (LLTO) were synthesized using the citrate route. Four samples were prepared in different atmospheres: air, synthetic air, oxygen and argon to evaluate the influence of the presence of moisture and gas composition. The crystal structure was analysed by Rietveld refinement of X-ray diffraction data and the microstructure observed by transmission electron microscopy (TEM). The conductivity of the samples was measured by impedance spectroscopy and 7Li and 1H-NMR analyses enable to follow the corrosion process and its influence on the ion mobility. Results and Discussion We observed that LLTO is air-sensitive and its transport properties are highly influenced by moisture during the processing. A corrosion process occurs at the surface of the grains forming an insulating lithium carbonate phase after consecutive reactions with H2O and CO2[3]. This secondary phase prohibits the lithium diffusion from grain to grain and is responsible forthe increase of the grain boundary resistivity. A clear understanding of lithium diffusion was obtained by impedance and NMR experiments as it reveals the presence of lithium ion blocking secondary phase and its dramatic effect on the grain boundary conductivity. The room temperature conductivity at the grain boundary can be increased by almost a decade when using dry sintering atmospheres as it prevents the protonation of the surface of the particles by Li-H exchange as observed by TEM. The sintering atmosphere plays also a crucial role for the densification of the ceramics. Conclusions The grain boundary resistivity issue in LLTO ceramics has been identified and then solved by using moisture-free atmospheres during the material processing. These results offer new prospect of cost effective processing of high conductivity ceramic materials for applications in Li battery technologies.

Visualization of O2 on Aqueous Li-Air Battery by Using Microfocus X-ray CT

The reaction products associated with charge/discharge processes are key issues to improve the performance of Li-air battery. Although LiO2, Li2O2, and other Li organic compounds have been previously investigated, the production of O2 during the charge process and its ability to cause reduction of the electrode area have not been discussed. In this study, experimental visualization of the inside of an air cathode was realized using microfocus X-ray computed tomography (CT), and the production of O2 in aqueous electrolyte by the charge reaction was visualized. As a result, we show that the wettability of the porous cathode carbon electrode strongly affected the behavior of produced gas.

H+ diffusion and electrochemical stability of Li1+x+yAlxTi2−xSiyP3−yO12 glass in aqueous Li/air battery electrolytes

It is well known that LATP (Li1+x+yAlxTi2−xSiyP3−yO12) glass is a good lithium (Li)-ion conductor. However, the interaction between LATP glass and H+ ions in aqueous electrolytes (including the diffusion and surface adsorption of H+ ions) needs to be well understood before the long-term application of LATP glass in an aqueous electrolyte can be realized. In this work, we investigate H+-ion diffusion in LATP glass and their interactions with the glass surface using both experimental and modeling approaches. Our results indicate that the apparent H+-related current observed in the initial cyclic voltammetry scan should be attributed to the adsorption of H+ ions on the LATP glass rather than the bulk diffusion of H+ ions. Furthermore, density functional theory calculations indicate that the H+-ion diffusion energy barrier (3.21 eV) is much higher than that for Li+ ions (0.79 eV) and Na+ ions (0.79 eV) in a NASICON-type LiTi2(PO4)3 material. As a result, H+-ion conductivity in LATP glass is negligible at room temperature. However, significant surface corrosion was found after the LATP glass in a strong alkaline electrolyte. Therefore, to prevent LATP glass from corrosion, appropriate electrolytes must be developed for long-term operation of LATP in aqueous Li–air batteries.

Mechanical properties of the solid Li-ion conducting electrolyte: Li0.33La0.57TiO3

Li0.33La0.57TiO3 (LLTO) is a potential Li-ion conducting membrane for use in aqueous Li-air batteries. To be in this configuration its mechanical properties must be determined. Dense LLTO was prepared using a solid-state (SS) or sol–gel (SG) procedure and was hot-pressed to yield a high relative density material (>95 %). Young’s modulus, hardness, and fracture toughness of the LLTO-SS and sol–gel LLTO-SG materials was determined and compared to other solid Li-ion conducting electrolytes. The Young’s modulus for LLTO-SG and LLTO-SS was 186 ± 4 and 200 ± 3 GPa, respectively. The Vickers hardness of LLTO-SG and LLTO-SS was 9.7 ± 0.7 and 9.2 ± 0.2 GPa, respectively. The fracture toughness, K IC, of both LLTO-SG and LLTO-SS was ~1 MPa m1/2; the fracture toughness of LLTO-SG was slightly higher than that of LLTO-SS. Both LLTO-SG and LLTO-SS have a Young’s modulus and hardness greater than the other possible solid Li-ion conducting membranes; Li7La3Zr2O12 and Li1+x+y Al x Ti2−x Si y P3−y O12. Based on modulus and hardness hot-pressed LLTO exhibits sufficient mechanical integrity to be used as a solid Li-ion conducting membrane in aqueous Li-air batteries but, its fracture toughness needs to be improved without degrading its ionic conductivity.

Effects of aqueous electrolytes on the voltage behaviors of rechargeable Li-air batteries

Aqueous Li-air batteries have attracted a great deal of attention due to their high theoretical energy capacities. However, while still in the early stages of research, the reported energy capacities of Li-air batteries are far from what has been theoretically predicted. In this research, we have designed a Li-air battery that has a Li ǀ organic liquid electrolyte ǀ Li+-conducting glass ceramic plate (LiGC plate) ǀ aqueous electrolyte ǀ Pt air electrode structure and studied the impacts of the compositions of the aqueous electrolyte on the battery performance. With lower concentrations of alkali aqueous electrolytes (≤0.05M LiOH), a discharge voltage of approximately 3.5V (at 0.05mAcm−2) and a voltage efficiency up to 84% were observed. The addition of LiClO4 into the aqueous solution slightly lowered the discharge voltage to 3.3V but dramatically decreased the internal resistance of the battery to 35.4Ωcm−2. With a charge voltage plateau observed at 3.90V at a current of 0.05mAcm−2, the Li ǀ organic liquid electrolyte ǀ LiGC ǀ 1M LiClO4 ǀ Pt air battery showed an 85% voltage efficiency at room temperature. Adding LiClO4 into the aqueous electrolytes resulted in an impedance reduction and slowed the pH increase of the alkaline-based electrolyte due to the fast or long-term discharge of the air electrode in the Li-air battery. The discharge and charge voltage behaviors of the battery and the changes to the pH values of the aqueous electrolyte at different current rates were also recorded and are presented in this paper.

An Aqueous Li-Air Battery Based on a Novel Reservoir Concept

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