Non-aqueous Lithium-air Batteries Research Articles

Towards High-Capacity Recovery Aprotic Li-O2 Batteries

Lithium-oxygen batteries (LOBs) have great potential as energy storage systems to accelerate the energy transition, due to their high theoretical energy density (up to 3505 Wh/kg), coupled to their low cost and environmental impact (transition metal free) [1]. The development of reversible Li-O2 batteries relies on the optimization of multiple interconnected factors, such as complex interactions affecting the activity of redox mediators (RM) [2-4]. Amongst these, the cycling protocols, electrolyte composition, and electrode structure are of crucial importance to achieve high capacity recovery, and thus reversibility [1, 5].Here, we study the interconnectivity of these factors, testing a range of electrode/electrolyte combinations using different cycling protocols to evaluate the capacity recovery, overpotentials, and lifetime of Li-O2 cells. Typically in the Li-O2 literature, constant current (CC) discharge-charge cycles are used to evaluate the performance of cells [1]. However, the slow OER kinetics, especially at the end of charge, make the use of CC protocols problematic, as increased overpotentials are required to meet the current demands (Figure top). Constant current – constant voltage (CCCV) protocols are more suitable to evaluate this technology, as they enable higher capacity recovery upon charging, while keeping the cells at potentials in which the parasitic reactions can be managed.Our results show significant increased capacity retention while keeping the charge limited to various upper cut-off potentials in cells without RM (Figure bottom). Cells with LiI as RM can recover 100% of the discharge capacity at relatively low potentials (3.5-3.7 V), providing longer cycle life than without RM or CC protocols. Furthermore, the influence of the structure in graphene-containing electrodes to the capacity recovery and lifetime is also explored with regards to the kinetics of the ORR and OER reactions.This study demonstrates how the interplay between cycling protocols, electrolyte composition and electrode structure affects the reversibility, and highlights the need for a comprehensive approach for developing reversible non-aqueous Li-O2 batteries. Gao, Z., et al., Recent Progress in Developing a LiOH-based Reversible Nonaqueous Lithium-Air Battery. Advanced Materials, 2023. 35: p. 2201384.Jónsson, E., et al., On the Solvation of Redox Mediators and Implications for their Reactivity in Li-Air Batteries. Journal of The Electrochemical Society, 2021. 168(3): p. 030529.Liu, T., et al., Understanding LiOH Formation in a Li-O2 Battery with LiI and H2O Additives. ACS Catalysis, 2018. 9: p. 66-77.Temprano, I., et al., Toward Reversible and Moisture-Tolerant Aprotic Lithium-Air Batteries. Joule, 2020. 4: p. 1-20.Liu, T., et al., Current Challenges and Routes Forward for Nonaqueous Lithium-Air Batteries. Chem Rev, 2020. 120(14): p. 6558-6625. Figure 1

Study on performance of hybrid lithium-air batteries with different alkaline cation pairs in ambient environment

Hybrid lithium-air batteries (HLABs) effectively solve the bottleneck problem of discharge product Li2O2 blocking non-aqueous lithium-air batteries' electrode pores, attracting extensive attention. This paper analyzes the battery's cycle performance, deep discharge performance, and main failure reasons in an ambient environment using the LiOH and KOH aqueous solutions as cathode electrolytes. Meanwhile, the authors intensely study the internal mechanism of mass transfer by molecular dynamics simulation method based on these two cases of electrolytes. The KOH aqueous solution as cathode electrolytes of HLABs has superior deep discharge performance due to the better diffusion ability of K+, and the hydration of cations weakened. However, because the KOH is more alkaline than LiOH, the corrosion on LAGP plates will be severe, affecting the battery's cycle performance. So, the cycle discharge performance of the LiOH aqueous solution as cathode electrolytes of HLABs is significantly better than that of the KOH solution. Under the external electric field, the hydration of cations weakened, which is more favorable to the mass transfer of batteries. Therefore, the HLABs with KOH perform better in deep discharge, and the HLABs with LiOH perform better in long cycles. The research results provide a particular reference for subsequent research and application.

Recent Progress in Developing a LiOH-Based Reversible Nonaqueous Lithium-Air Battery.

The realization of practical nonaqueous lithium-air batteries (LABs) calls for novel strategies to address their numerous theoretical and technical challenges. LiOH formation/decomposition has recently been proposed as a promising alternative route to cycling LABs via Li2 O2 . Herein, the progress in developing LiOH-based nonaqueous LABs is reviewed. Various catalytic systems, either soluble or solid-state, that can activate a LiOH-based electrochemistry are compared in detail, with emphasis in providing an updated understanding of the oxygen reduction and evolution reactions in nonaqueous media.Weidentify the key factors that can switch the cell chemistry between Li2 O2 and LiOH and highlight the debate around these routes, as well as rationalize potential causes for these opposing opinions. The identities of the reaction intermediates, activity of redox mediators and additives, location of reaction interfaces, causes of parasitic reactions, as well as the effect of CO2 on the LiOH electrochemistry, all play a critical role in altering the relative rates of a series of interconnected reactions and all warrant further investigation.

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.

Insoluble Solid Organic Catalysts for Non-Aqueous Lithium-Air Batteries

The chemistries based on the Li-O2 couple in aprotic electrolyte seem promising to provide ultrahigh-energy density values and outperform the current LIB technology. The main targeted application is to power electrified vehicles, with the hope of achieving high driving range. Unfortunately, serious side-reaction issues have plagued their development for practical applications so far. For example, during the discharge process, undesired insulating products are formed instead of lithium peroxide. Moreover, the blocking/clogging effect on the air electrode due to a deposition process leads to an overpotential during both the discharge (Oxygen Reduction Reaction: ORR) and charge processes (Oxygen Evolution Reaction: OER), which results in electrode degradation, electrolyte decomposition and precocious cell failure.A promising strategy to reduce these overpotentials is the use of organic redox mediators by taking advantage of their tunability. For several years, our group has been developing lithiated organic materials with average redox potentials close to the O2/Li2O2 redox couple (2.96 V vs Li+/Li0). We here report the effect of Li2DAnT (alone or in combination with Li4-p-DHT [1]) and Li4-DHNDC [2] on the cycling behavior of Li-O2 batteries and their influence on ORR and OER processes. References 1) S. Renault, et al., PCT Patent WO 2021/148835 A1.2) S. Renault, et al., PCT Patent WO 2021/148836 A1. Figure 1

Study on Two-Phase Permeation of Oxygen and Electrolyte in Lithium Air Battery Electrode Based on Digital Twin

In this paper, the saturation of electrolytes on the mass transfer property of porous electrodes in non-aqueous lithium air batteries has been studied based on digital twin. Herein, we reconstruct the porous cathode based on X-ray micro-computed tomography (μct) and quantitatively analyze the pore size distribution, specific surface area, triple-phase interface area, conductivity and diffusion coefficient of reactants at varying filling degrees of the electrolyte. The results derived from digital twin provide insight into the gas–liquid two-phase mass transfer performance in the porous cathode with various degrees of electrolyte saturation and demonstrate that the optimum electrolyte saturation is 60%.

(Digital Presentation) Mass Spectroscopic Products Analysis during Charging of Li-O2 Cell with Tegdme Based Electrolyte

Rechargeable lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. Despite significant efforts by many research groups, LAB is still far from practical use and many problems must be overcome [1]. The first problem is associated with the use of air as it contains many components other than oxygen including N2, water, and CO2, which interfere battery reactions. Thus, most of the fundamental studies are not on LAB but on Lithium-oxygen battery (LOB), which uses pure oxygen as an active material. Even LOB has many serious problems, including low cyclability caused by (1) high charging overpotential, which induces degradation of positive electrode (carbon) and electrolyte solution, and (2) degradation/dendrite formation of negative Li metal electrode. To improve the cyclability, it is essential to clarify the mechanism of degradation of electrodes and electrolyte.Here we employed mass spectroscopy to follow products generation during charging so that we can clarify the degradation mechanisms of electrodes and electrolyte. Porous carbon sheet (KJCNT from KJ Specialty Paper), lithium metal (Honjo Metal), 1 M LiTFSI TEGDME (both from Sigma-Aldrich) solution, PE separator (W-Scope), and stainless steel mesh (Hohsen) were used as positive electrode, negative electrode, electrolyte, separator, and gas diffusion layer, respectively. Isotope exchanged TEGDME, i.e., 13CH3-TEGDME and CD3-TEGDME, which were synthesized in our laboratory, and 18O2 (Taiyo Nippon Sanso) were used for mass spectroscopy for precise products assignments. Details of set-up for mass analysis have been reported elsewhere [2]. We carried out online QMS (Quadrupole Mass Spectrometer) measurement for mass numbers of decomposition products between 12-90 during the potential sweep from OCP to 4.8 V (0.05 mV/s).Figure 1 shows the current and mass signals of m/z = 18 (H2O), 32 (O2), and 44 (CO2) as a function of potential. It is clear that current increased immediately as potential was scanned from OCP (~2.8 V ), reached a maximum at 3.3 V, decreased gradually, reached a minimum at 4.0 V, increased again to reach a maximum at 4.4 V, decreased to reach a minimum at 4.6 V and increased again. The potential dependence of O2 signal is very similar to that of current as the main battery reaction is Li2O2 → 2Li+ + O2 + 2e-. Two clear peaks were observed at around 3.3 V and 4.4V, showing the presence of two kinds of Li2O2 [3]. The H2O signal started to increase just after the 1st current/O2 peaks where the current efficiency for O2 generation current efficiency started to decrease, suggesting the H2O formation is related to the decrease of the current efficiency. The CO2 signal started to be significant at 4.1 V where current and the O2 signals started to increase again and reached a maximum at ca. 4.5 V, which is more positive than those of current and O2 signal but equal to H2O peak. Although current increased again significantly at potentials more positive than 4.65 V, no mass signals of O2, H2O and CO2 increased. Instead signals such as m/z = 15, 29, 31, 45, and 60, which are related to organic molecules derived from TEGDME, became significant. Figure 2 shows the online QMS results at 4.65 V. We can see that various mass signals such as 15, 29, etc. were observed at this potential. By careful analysis of the results with the assistance of isotopes 18O2, 13CH3-TEGDME, and CD3-TEGDME, presence of CH3OH, HCHO and other organic molecules with high vapor pressure originated from TEGDME were confirmed. Additionally, we detected molecules with low vapor pressure such as CH3O(CH2)2OH, CH3OCH2COCH3, etc., which were derived from TEGDME by GC/MS analysis of samples collected every 1hr. Based on the products detected by online QMS and GC/MS, possible degradation mechanism of electrolyte can be deduced. I will discuss the degradation mechanism of electrolyte based on the above results.[1] Liu T., et al. Current challenges and routes forward for nonaqueous lithium–air batteries. Chemical reviews, 2020, 120(14): 6558-6625.[2] Ue, M., et al. Material balance in the O2 electrode of Li–O2 cells with a porous carbon electrode and TEGDME-based electrolytes, RSC Advances, 2020, 10(70): 42971 - 42982.[3] Nishioka K, et al. Isotopic depth profiling of discharge products identifies reactive interfaces in an aprotic Li–O2 battery with a redox mediator. Journal of the American Chemical Society, 2021, 143(19): 7394-7401. Figure 1

Understanding the Transport of Atmospheric Gases in Liquid Electrolytes for Lithium–Air Batteries

In metal–air batteries, carbon dioxide (CO2) and nitrogen (N2) are, apart from oxygen (O2), also present as dissolved species in the liquid electrolyte. These dissolved gases can strongly influence the battery performance, as they affect the discharge mechanism and the stability of the lithium metal anode. Therefore, their solubility and diffusivity are important parameters, that are rarely considered in the development of electrolytes for metal–air batteries. In this work, the diffusion coefficients (D) and Henry’s law solubility constants (H cp ) of O2, N2 and CO2 in common ether-based (diglyme (2G), triglyme (3G) and tetraglyme (4G)) and DMSO-based electrolytes are measured by means of gas uptake measurements. Additionally, the diffusion coefficients are calculated through molecular dynamics simulations. The results agree well with the experimental data. Furthermore, the influence of solvent parameters, such as surface tension and viscosity, on the solubility and the diffusivity as well as the impact of the addition of LiTFSI as conducting salt are investigated. The reported data will help to assess the impact of dissolved gases on the cell chemistry of nonaqueous lithium–air batteries, especially on the solid electrolyte interphase (SEI) at the lithium anode, and to predict diffusivity and gas solubility in other electrolytes.

Current Challenges and Routes Forward for Nonaqueous Lithium-Air Batteries.

Nonaqueous lithium-air batteries have garnered considerable research interest over the past decade due to their extremely high theoretical energy densities and potentially low cost. Significant advances have been achieved both in the mechanistic understanding of the cell reactions and in the development of effective strategies to help realize a practical energy storage device. By drawing attention to reports published mainly within the past 8 years, this review provides an updated mechanistic picture of the lithium peroxide based cell reactions and highlights key remaining challenges, including those due to the parasitic processes occurring at the reaction product-electrolyte, product-cathode, electrolyte-cathode, and electrolyte-anode interfaces. We introduce the fundamental principles and critically evaluate the effectiveness of the different strategies that have been proposed to mitigate the various issues of this chemistry, which include the use of solid catalysts, redox mediators, solvating additives for oxygen reaction intermediates, gas separation membranes, etc. Recently established cell chemistries based on the superoxide, hydroxide, and oxide phases are also summarized and discussed.

Critical Advances in Ambient Air Operation of Nonaqueous Rechargeable Li-Air Batteries.

Over the past few years, great attention has been given to nonaqueous lithium-air batteries owing to their ultrahigh theoretical energy density when compared with other energy storage systems. Most of the research interest, however, is dedicated to batteries operating in pure or dry oxygen atmospheres, while Li-air batteries that operate in ambient air still face big challenges. The biggest challenges are H2 O and CO2 that exist in ambient air, which can not only form byproducts with discharge products (Li2 O2 ), but also react with the electrolyte and the Li anode. To this end, recent progress in understanding the chemical and electrochemical reactions of Li-air batteries in ambient air is critical for the development and application of true Li-air batteries. Oxygen-selective membranes, multifunctional catalysts, and electrolyte alternatives for ambient air operational Li-air batteries are presented and discussed comprehensively. In addition, separator modification and Li anode protection are covered. Furthermore, the challenges and directions for the future development of Li-air batteries are presented.

Carbon-Based Cathode Materials for Non-Aqueous Lithium-Air Batteries

Carbon-Based Cathode Materials for Non-Aqueous Lithium-Air Batteries

Cycling Non-Aqueous Lithium-Air Batteries with Dimethyl Sulfoxide and Sulfolane Co-Solvent

Despite considerable research efforts, finding a chemically stable electrolyte mixture in the presence of reduced oxygen species remains a great challenge. Previously, dimethyl sulfoxide (DMSO) and sulfolane (tetramethylene sulfone (TMS))-based electrolytes were reported to be stable for lithium air (Li-O2) battery applications. Recently lithium hydroxide (LiOH) based chemistries have been demonstrated to involve supressed side reactions in water-added ether- and DMSO-based electrolytes. Herein, we investigate the impact of DMSO-based electrolyte and sulfolane co-solvent on cell chemistry in the presence of water. We found that DMSO-based electrolyte leads to formation of a peroxide-hydroxide mixture as discharge products and the removal of both LiOH and lithium peroxide (Li2O2) on charging from 3.2–3.6 V (vs. Li+/Li) is observed. In the presence of sulfolane as co-solvent, a mixture of Li2O2 and LiOH is formed as major discharge products with slightly more LiOH formation than in the absence of sulfolane. The presence of sulfolane has also significant effects on the charging behaviour, exhibiting a clearer 3 e−/O2 oxygen evolution reaction profile during the entire charging process. This work provides insights into understanding the effects of the primary solvent on promoting LiOH formation and decomposition in lithium iodide (LiI) mediated non-aqueous Li-O2 batteries.

Flexible Metal–Air Batteries: Progress, Challenges, and Perspectives

AbstractFlexible metal–air batteries, which are a promising candidate for implantation in wearable or rolling‐up electronic devices, have attracted much attention recently due to their relatively high energy density. Various flexible metal–air batteries have been developed recently, including flexible nonaqueous lithium–air batteries, aqueous zinc–air batteries, and aqueous aluminum–air batteries. Although various viable configurations of flexible metal–air batteries have been proposed, challenges regarding electrode design, electrolyte exploitation, and low practical energy density, still exist. Here, a brief introduction is presented as to the recent development of flexible metal–air batteries, regarding the electrodes, electrolyte, and prototype devices. Also, a general perspective on the current challenges and recommended future research directions for the practical use of metal–air batteries is provided.

The Effects of Redox Mediators and Water Content on Oxygen Evolution for Li-Air Batteries

Chemistries that can demonstrate tolerance to both moisture and atmospheric carbon dioxide have the power to advance the technology readiness level of non-aqueous lithium air batteries. Previously published results have found that lithium iodide as redox mediator in dimethoxyethane solvent containing high water content affords reversible cycling of a lithium oxygen battery via lithium hydroxide[1]. In collaboration with the authors of the previous work, this concept has been extended to explore additional redox mediators and alternative electrolyte mixtures. Quantitative oxygen evolution for the new chemistries was studied using continuous differential electrochemical mass spectroscopy. Oxygen evolution was found for some of the new chemistries employed. Faradaic efficiency for oxygen evolution and Tafel analysis shows complex behaviour. Discharge product analysis shows that some of the new chemistries which afford oxygen evolution also cycle via lithium hydroxide.[1] Liu, et al. Science, 2015, 350, 6260, p530.

Ultrathin CuCo2O4 Nanosheets on Carbon Textiles as Flexible Cathodes for Bendable Lithium-Air Batteries

In this work, ultrathin mesoporous CuCo2O4 nanosheets (CCO NSs) have been in-situ grown on carbon textiles (CTs) via a facile hydrothermal method and a post annealed treatment. This composite can be directly used as flexible cathodes for bendable non-aqueous lithium-air batteries. Benefitting from the unique architecture and material superiority, the coin-type batteries show large specific capacity of 11793 mAh g−1 with small potential gap of 0.95 V and exhibit considerable cycle stability for over 65 times without obviously degradation. This structural feature not only provides high surface area and large open spaces but also ensures efficient transmission for lithium ion and oxygen and fast transporting of electrons. Furthermore, bendable lithium-air batteries have been assembled and cycle for over 46 times, which confirms its application in foldable devices.

Effects of moist air on the cycling performance of non-aqueous lithium-air batteries

Most non-aqueous lithium-air batteries reported in the literature are limited to operating with pure oxygen. To practically operate the battery in ambient air, understanding how the battery’s performance varies with humidity of moist air is essential. Here we study the effects of moist air on the cycling performance through operating a non-aqueous lithium-air battery with a stable anode and a nano-structured RuO2/NiO cathode at various relative humidities. Results show that in the dry air, the discharge and charge terminal voltages are around 2.51 and 4.12V, respectively, but change to 2.79 and 3.87V when the relative humidity reaches 84%. The energy efficiencies corresponding to the dry air and the relative humidity of 84% are 66.2% and 73.8%, respectively. The improved performance is found to be mainly due to the increased fraction of LiOH among the discharge products at high relative humidities. The discharge voltage for the formation of LiOH is higher than that for the formation of Li2O2, while the charge voltage for the decomposition of LiOH is lower than that for the decomposition of Li2O2. The results suggest that to enable a non-aqueous lithium-air battery to operate in moist air, in addition to protecting the lithium anode from water, designing a cathode with electrocatalytic activities for the decomposition of both Li2O2 and LiOH is required.

Rechargeable Aqueous Lithium-Air Batteries

The lithium-air battery is a promising power source for electric vehicles because of its high theoretical specific energy density. Two types of the lithium-air battery are proposed, namely, non-aqueous and aqueous systems [1]. The theoretical specific energy densities of the non-aqueous and aqueous systems are 3458 and 1910 Wh kg-1, respectively. However there are many changeable research drawbacks that must still be addressed. At present, non-aqueous lithium air battery is mainly focused, but this system has severe problems such as lithium corrosion by water, high polarization during charge process, etc. The aqueous lithium-air system could avoid these problems by using water stable lithium electrode [2] and aqueous electrolyte. In this study, we demonstrate the cell performance of the aqueous lithium-air system. The laminate type cell was tested at room temperature. The cell was consisted of Li/interlayer/water stable lithium conducting solid electrolyte/aqueous electrolyte/air electrode. As the interlayer, a non-aqueous electrolyte such as Li(FSO2)2N in glyme [3] was used, because the water stable lithium conducting solid electrolyte of Li1+xAlxTi2-x(PO4)3 (LATP) is unstable in contact with lithium. The LATP plate of ca. 0.15 mm in thickness was supplied by Ohara Inc. Japan. The platinum catalyst coated carbon sheet for a large size cell and the composite electrode of carbon black (KB) supported MnO2 catalyst for a small size cell were used as the air electrodes, respectively. The cells were operated under open air. The impedance profiles of the test cells with different interlayer electrolytes of glyme were examined. The profiles showed two semi-circles. The high frequency semi-circle showed no dependence on the character of the interlayers, but the low frequency semi-circle showed dependence on it. The high frequency semi-circle corresponds to the grain boundary resistance of the LATP plate and the second semi-circle to the interlayer resistance between lithium and interlayer electrolyte. The lowest cell resistance of ca. 270 Ω cm2 at room temperature was observed for the Li/DME-LiTFSI/LTAP/saturated LiCl aqueous solution/C cell. A large size cell of 6.2 Ah was successfully discharged at 50 °C with 2 mA cm-2 for 150 h. The initial cell voltage of 3.0 V was gradually decreased to 2.7 V after 150 h polarization. A cycle performance of the small size cell was examined at room temperature. For a single cycle, the charge-discharge test was performed with 2 mA cm-2 for 4 h. The discharge and charge voltages were not changed significantly for 100 cycle and 400 h. In conclusion, the aqueous lithium air battery was operated with high current density at room temperature under open air. These results suggest that aqueous lithium-air rechargeable batteries have a possibility for further development with high specific energy and power density.

Carbon Coated Mesoporous CeO2 on Graphene Foam As Flexible Cathode in Lithium-Air Batteries

With the rapid development of foldable electronics in recent years, flexible energy storages have received extensive attention. As the key component, several prototypes such as flexible supercapacitors, li-ion batteries, and solar cells have been developed for practical application. However, low theoretical energy density of these power storages will limit their application in new flexible device. Therefore, non-aqueous lithium-air batteries have been developed for their extremely high theoretical specific energy density about 3600 Wh·kg-1, 3-5 times higher than that of the current lithium-ion batteries1, 2. When used in ambient air as flexible batteries, several problems must be overcome: (1) lithium anode should be protected from CO2 and H2O, (2) catalyst of high activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) should be introduced at lower oxygen partial pressure3. Thus the structure of the air cathode should be optimized. Macroporous along with mesoporous with high specific surface area should be introduced for the effective adsorption of O2 on the active sites, as well as the enhanced transportation of the reactants and intermediate species on the catalyst4. In our studies, mesoporous CeO2 microspheres were synthesized through hydrothermal process on 3D macrospores graphene foam as flexible cathode. CeO2 microspheres with the size of ~ 300 nm are distributed uniformly on the surface of 3D graphene foam with carbon coated for enhanced electrical conductivity. With the macroporous provided by 3D graphene foam for O2 diffusion and the mesoporous CeO2for enhanced catalytic activity towards ORR and OER, the LABs show better reversible capacity. And the detailed morphological and electrochemical analysis will be discussed in the presentation.

Non-Aqueous Li-Air Flow Battery: Improving Capacity and Current Density through Cathode Optimization

Non-aqueous Lithium-air (Li-air) batteries are attractive energy storage systems due to their exceptionally high theoretical energy density. Despite its high energy density, issues such as cycle fading and low current density still need to be overcome. A major cause of these issues is the deposition of discharge products on the surface as well as inside the pores of the cathode. These deposits clog the pores and prevent continuous steady discharge. Recently we developed a Li-air battery configuration that has a flowing Li-ion free ionic liquid as the electrolyte, enabling the continuous removal of discharge products (Figure 1). This flow battery consists of two units, a flow battery for electrochemical reaction and a storage site for discharge products. In detail, a gas diffusion electrode (GDE) allows continuous supply of O2while fresh catholyte is continuously provided to transport discharge products away to the storage. Also, the Li metal anode is separated from the catholyte by a solid state Li-ion conducting separator. We successfully demonstrated separation of the electrochemical reaction on the cathode and storage of the discharge products by employing a flowing catholyte. This approach led to the flowing Li-air battery exhibiting a higher discharge capacity than a static Li-air battery (i.e. with a non-flowing electrolyte configuration). However, the discharge current density achieved with this Li-air flow battery was still low. To improve the discharge current density of the Li-air flow battery, we used COMSOL modelling to determine parameters that are key in optimizing battery performance modeling in COMSOL. We simulated a modified version of Li-air battery model, based on a model presented in prior work.1 This model identified optimal parameters for the cathode, including the porosity of electrode and the depth of immersion of the cathode with electrolyte. The maximum current density that can be achieved increases as the porosity of the cathode increases because a higher porosity improves O2 transport. However, a different trend was observed for the depth by which the electrolyte had penetrated the cathode. The maximum current density is observed at 30 and 50 µm for an initial concentration of O2 of 5 and 15 mol m3, respectively, suggesting that an optimum electrolyte immersion depth is key to achieve the highest current density. In parallel with these modeling efforts, the structure and surface of GDEs were modified and evaluated to increase discharge current density for Li-air flow battery. Specifically, we fabricated and evaluated hot-pressed GDEs, super-hydrophobic GDEs coated with PTFE, and GDEs on which additional material had been deposited. Especially the hot-pressed GDEs exhibited improved discharge current density, which we attribute to the hot-pressing decreasing the thickness of GDEs, thus enabling better O2transport. In summary, we established the concept of a Li-air battery with a flowing Li-ion free non-aqueous electrolyte. Also, we used modeling and experiments to analyze how different parameters, specifically the properties of the cathode, benefit the performance of the non-aqueous Li-air flow battery. We were able to optimize the gas diffusion electrode-based cathode for this Li-air flow battery, which lead to higher discharge current densities.

Phthalocyanines Based Two-Phase Catalysts for Lithium Oxygen Batteries

Li-air batteries, which are considered to offer much higher energy density than the current Li-ion batteries suffer from poor cycle life due to electrolyte decomposition and clogging of the air cathode by insoluble discharge products. Efficient bifunctional catalysts could improve the stability of Li-air batteries by lowering the overpotential and prolonging the battery cycle life. This study focuses on Iron phthalocyanines (FePc) as possible bifunctional electrocatalysts. Metal phthalocyanines were utilized mainly because of their structural analogy which could be fine- tuned by the metal being used, accessibility, and low cost. In this work, firstly, FePc supported on graphite nanofibres (GNF) was investigated as solid electrocatalyst in non-aqueous LiTFSI (TEGDME) electrolyte. Secondly, FePc was dissolved in the non-aqueous electrolyte and studied as liquid catalyst with GNF cathode. FePc/GNF (solid catalyst) delivered superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable to that of commercial Pt/C. FePc_electrolyte (liquid catalyst) exhibited a steady profile for chronoamperometry, and good diffusivity of lithium ions as measured from electrochemical impedance spectroscopy. The bifunctional catalysts when applied as electrocatalysts in non-aqueous lithium air batteries delivered better electrochemical performance mainly by reducing the large overpotential associated with ORR and OER. Both the cells with solid and soluble FePc exhibited better reversibility and cyclability. The performance of FePc catalyst as solid and liquid has been comparative analyzed in detail.