Li O2 System Research Articles

Constructing in-situ SOCl2-induced protective layer on Li anode for high-performance Li–O2 batteries containing LiI redox mediator

Li–O2 batteries have attracted wide attention on account of the ever-increasing demand of high energy density systems. However, their practical application is still facing many critical problems, especially the slurry reaction rate/serious side reactions on cathodes and the fast growth of Li dendrites/passivating layers on anodes. Therefore, we design an in-situ formed coating layer on Li metal anode by introducing thionyl chloride (SOCl2) additives into the Li–O2 system with a redox mediator (RM), LiI. The robust and uniform SOCl2-derived layer can effectively prevent the attack of O2/O2–, which inhibits the surface passivation of Li metal anode and greatly supresses the infinite dendrite growth. Additionally, the SOCl2 additive also contributes to a certain specific capacity of the Li–O2 cells at full discharge/charge conditions. Moreover, the SOCl2-derived coating layer can almost completely stop the diffusion of the soluble I-based RM on Li metal anode to eliminate contiunous side reactions between them. The symmetrical batteries containing SOCl2 display lower overpotentials and longer cycling life than those of cells without SOCl2. More importantly, the SOCl2 based Li–O2 batteries with LiI exhibit the extra-high capacity (31000 mAh g−1), ultra-small voltage polarization (∼1.4 V), and extended operation life (190 cycles).

Disentangling Plasmonic and Catalytic Effects in a Practical Plasmon-Enhanced Lithium–Oxygen Battery

Rechargeable Li–O2 batteries have high theoretical energy density (~3600 Wh kg-1) compared to the conventional Li–ion batteries. However, the recharging process is primarily disturbed by the large overpotential attributed to the sluggish OER kinetics. Very recently, photo-assisted Li–O2 batteries with semiconductor-containing cathodes have gained attention as a promising approach for enhanced energy storage. Surface plasmon resonance (SPR), the unique property of plasmonic materials (such as Au, Ag, Cu, Pd, and Al) interacting with light, has found increasing application in catalysis. Here, we demonstrate plasmonic effects in Li–O2 systems by incorporating gold nanoparticles on a practical Ketjen Black cathode with different amounts and sizes. During discharge, plasmonic Au NPs induce a Li2O2 morphology change to small particles, which are easily decomposed during recharge. Most importantly, the SPR-induced hot carriers help to form and decompose Li2O2 and suppress carboxylate side-products, decreasing recharge voltages and increasing the round-trip efficiency up to 80.2%. Meticulous analyses of the catalytic properties of the Au NPs and the SPR-induced near-field enhancement and local heat effects are here additionally shared.

Oxygen Vacancy-Mediated Growth of Amorphous Discharge Products toward an Ultrawide Band Light-Assisted Li-O2 Batteries.

Photoassisted electrochemical reaction is regarded as an effective approach to reduce the overpotential of lithium-oxygen (Li-O2 ) batteries. However, the achievement of both broadband absorption and long term battery cycling stability are still a formidable challenge. Herein, an oxygen vacancy-mediated fast kinetics for a photoassisted Li-O2 system is developed with a silver/bismuth molybdate (Ag/Bi2 MoO6 ) hybrid cathode. The cathode can offer both double advantages for light absorption covering UV to visible region and excellent electrochemical activity for O2 . Upon discharging, the photoexcited electrons from Ag nanoplate based on the localized surface plasmon resonance (LSPR) are injected into the oxygen vacancy in Bi2 MoO6 . The fast oxygen reaction kinetics generate the amorphous Li2 O2 , and the discharge plateau is improved to 3.05V. Upon charging, the photoexcited holes are capable to decompose amorphous Li2 O2 promptly, yielding a very low charge plateau of 3.25V. A first cycle round-trip efficiency is 93.8% and retention of 70% over 500 h, which is the longest cycle life ever reported in photoassisted Li-O2 batteries. This work offers a general and reliable strategy for boosting the electrochemical kinetics by tailoring the crystalline of Li2 O2 with wide-band light.

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides

The Li−Ni−O phase diagram contains a variety of compounds, most of which are electrochemically active in Li-ion batteries [1-2]. LiNiO2 (LNO) is particularly well-known due to its behavior as cathode active material, potentially excellent but in practice plagued by several instability issues, which ultimately led to elemental substitutions of Ni with Co, Mn and Al towards NCM and NCA materials. A significant amount of understanding on LNO and on the elemental substitution it can allow were developed in the group of Claude Delmas [3]. In this contribution, I will briefly review the Li−Ni−O phase diagram, its history and the special role LNO occupies in it, with a focus on its synthesis, structure and decomposition [4-6]. Additionally, Li-rich phases of composition nearing Li2NiO3 will be discussed [7-9]. I will report a facile solid-state method to prepare Li2NiO3 and other Li-rich Ni oxides of composition Li1+xNi1−xO2 (0 ≤ x ≤ 0.33) [10]. I will also detail their crystal and electronic structure, exhibiting a highly oxidized Ni state and defects of various nature (Li−Ni disorder, stacking faults, oxygen vacancies). Moreover, the use of Li2NiO3 as a cathode active material has been investigated. It shows remarkably high specific capacity, which however fades quickly. While we demonstrate that the initial capacity is due to irreversible O2 release, such process stops quickly in favor of more classical reversible redox mechanisms that allow cycling the material for >100 cycles. After the severe oxygen loss (∼15−20%) and prolonged cycling, the Bragg reflections of Li2NiO3 disappear. Analysis of the diffracted intensities suggests the resulting phase is a disordered rock salt-type material with high Li content, close to Li0.5Ni0.5O, never reported to date and capable of Li diffusion. Our findings demonstrate that the Li−Ni−O phase diagram has not been fully investigated yet, especially concerning the preparation of new promising materials by out-of-equilibrium methods.Bibliography[1] Dahn, J., Vonsacken, U., Michal, C. A., Structure and Electrochemistry of Li1+-yNiO2 and a New Li2NiO2 Phase with the Ni(OH)2 Structure, Solid State Ionics, 1991, 44, (1-2), 87-97[2] Goodenough, J. B.; Wickham, D. G.; Croft, W. J. Some Magnetic and Crystallographic Properties of the System Lix +Ni1−2x +2Nix +++O. J.Phys. Chem. Solids 1958, 5 (1−2), 107−116.[3] Delmas, C., Menetrier, M., Croguennec, L., Saadoune, I., Rougier, A., Pouillerie, C., Prado, G., Grune, M., Fournes, L., An overview of the Li(Ni,M)O2 systems: syntheses, structures and properties, Electrochimica Acta, 1999, 45, (1-2), 243-253[4] Bianchini, M.; Roca-Ayats, M.; Hartmann, P.; Brezesinski, T.; Janek, J. There and Back Again-The Journey of LiNiO2 as a Cathode Active Material. Angew. Chem., Int. Ed. 2019, 58, 10434−10458.[5] Delmas, C., Croguennec, L., Layered Li(Ni,M)O2 Systems as the Cathode Material in Lithium-Ion Batteries, MRS Bullettin, 2002, 27 (8), 608-612[6] Bianchini, M.; Fauth, F.; Hartmann, P.; Brezesinski, T.; Janek, J, An in situ structural study on the synthesis and decomposition of LiNiO2, J. Mat. Chem. A, 2020, 8 (4), 1808-1820.[7] Migeon, H.; Courtois, A.; Zanne, M.; Gleitzer, C. Preparation and Study of Li2NiO3−y (y less-than-or-equal-to 0.135). Rev. Chim. Minér. 1976, 13 (1), 1−8.[8] Stoyanova, R.; Zhecheva, E.; Alcántara, R.; Tirado, J. L.; Bromiley, G.; Bromiley, F.; Boffa Ballaran, T. Lithium/nickel mixing in the transition metal layers of lithium nickelate: high-pressure synthesis of layered Li[LixNi1−x]O2 oxides as cathode materials for lithium-ion batteries. Solid State Ionics 2003, 161 (3), 197−204[9] Tabuchi, M.; Kuriyama, N.; Takamori, K.; Imanari, Y.; Nakane, K. Appearance of Lithium-Excess LiNiO2 with High Cyclability Synthesized by Thermal Decomposition Route from LiNiO2 - Li2NiO3 Solid Solution. J. Electrochem. Soc. 2016, 163 (10), A2312−A2317.[10] Bianchini M.; Schiele, A.; Schweidler S.; Sicolo, S.; Fauth, F.; Suard, E.; Indris, S.; Mazilkin, A.; Nagel, P.; Schuppler, S.; Merz, M.; Hartmann, P.; Brezesinski, T.; Janek, J.; From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides, Chem. Mater. 2020, 32, 9211−9227 Figure 1

Is Aluminum Useful in Ni-Rich Li-Ni-Mn-O Positive Electrode Materials for Lithium-Ion Batteries?

The low cost and high specific capacity of Ni-rich cathode active materials have made them promising materials for affordable, high performance Li-ion batteries. However, increasing the Ni-content in the cathode results in lower cycling performance and lower thermal stability.1 Meanwhile, lithium nickel manganese oxides (Li-Ni-Mn-O) are also inexpensive materials that benefit from high thermal stability and high energy density due to their high operation potential.2 Although manganese improves the performance of Ni-based materials, it also enables more cation mixing and reduces the rate capability of the cathodeAl-doping of cathode materials, although it lowers the initial capacity of the cell, has shown to reduce changes in the lattice of the material during delithiation resulting in improved cycling stability. The presence of Al in the lattice also decreases the charge-transfer resistance by facilitating Li-diffusion.3 Although the presence of Al has proved its virtue in commercial cathode materials such as LiNixCoyAl1-x-yO2 (NCA) and LiNixMnyCozAl1-x-y-zO2 (NMCA) it has yet to be used commercially in Co-free systems. In this work, Li(NixMn1-x)O2 (NM) systems of 3 different particle sizes (3.5 μm, 13 μm and 16 μm) as well as their Al-doped counterparts, Li(NixMn1-x-yAly)O2 (NMA), were studied. Figure 1 shows that the array of layered materials used in this study were optimally synthesized to be stoichiometric, single-phase materials with minimal cation mixing. Half cells and full cells were then constructed to evaluate the effect of Al on cycling stability, Li diffusion measurements were made to study rate capability and accelerated rate calorimetry was used to compare thermal stability. This head-to-head comparison of Li-Ni-Mn-systems with and without Al dopant will determine the effectiveness of Al in Ni-rich, Co-free cathode materials.References Li, H. et al. An Unavoidable Challenge for Ni-Rich Positive Electrode Materials for Lithium-Ion Batteries. (2019) doi: 10.1021/acs.chemmater.9b02372 Dou, S. Review and prospect of layered lithium nickel manganese oxide as cathode materials for Li-ion batteries. 911–926 (2013) doi.org/10.1007/s10008-012-1977-z Wang, G. X., Zhong, S., Bradhurst, D. H., Dou, S. X. & Liu, H. K. LiAlδNi1-δO2 solid solutions as cathodic materials for rechargeable lithium batteries. Solid State Ionics 116, 271–277 (1999). doi.org/10.1016/S0167-2738(98)00351-8 Figure 1

Nitrate Molten Salt Electrolytes with Iron Oxide Catalysts for Open and Sealed Li-O2 Batteries.

Li-O2 batteries with nitrate molten salt electrolytes are attracting considerable attention owing to their various electrochemical pathways to form a discharge product upon the open and sealed systems. Here, we investigate nitrate molten salt electrolyte-based open and sealed Li-O2 batteries with pristine and iron oxide catalysts. Through the systematic analysis of various Li-O2 battery characteristics, we observe the irreversible electrochemical reactions of the open Li-O2 battery with an iron oxide catalyst that erodes the battery performance due to the detrimental parasitic reaction of H2 gas evolution from the Li anode. In contrast, the sealed Li-O2 system with cathodes containing the iron oxide catalyst exhibits the formation and decomposition of Li2O discharge products without significant side reactions, which guarantees long cycle endurance, high-rate performance, and a gravimetric energy density. Thus, promising electrochemical results from the sealed Li-O2 system with the iron oxide catalyst provide a viable strategy for the high-performance molten salt-based Li-O2 battery.

Nanosponge-Based Composite Gel Polymer Electrolyte for Safer Li-O2 Batteries.

Li-O2 batteries represent a promising rechargeable battery candidate to answer the energy challenges our world is facing, thanks to their ultrahigh theoretical energy density. However, the poor cycling stability of the Li-O2 system and, overall, important safety issues due to the formation of Li dendrites, combined with the use of organic liquid electrolytes and O2 cross-over, inhibit their practical applications. As a solution to these various issues, we propose a composite gel polymer electrolyte consisting of a highly cross-linked polymer matrix, containing a dextrin-based nanosponge and activated with a liquid electrolyte. The polymer matrix, easily obtained by thermally activated one pot free radical polymerization in bulk, allows to limit dendrite nucleation and growth thanks to its cross-linked structure. At the same time, the nanosponge limits the O2 cross-over and avoids the formation of crystalline domains in the polymer matrix, which, combined with the liquid electrolyte, allows a good ionic conductivity at room temperature. Such a composite gel polymer electrolyte, tested in a cell containing Li metal as anode and a simple commercial gas diffusion layer, without any catalyst, as cathode demonstrates a full capacity of 5.05 mAh cm−2 as well as improved reversibility upon cycling, compared to a cell containing liquid electrolyte.

Electrochemical investigation of PVDF: HFP gel polymer electrolytes for quasi-solid-state Li-O2 batteries: effect of lithium salt type and concentration

Among rechargeable lithium batteries, lithium-oxygen batteries (Li-O2) offer remarkable energy densities which make them to be considered as the next generation energy storage systems. However, intrinsic problems arising from the use of liquid electrolytes has to be overcome before their adoption into the market. Gel-polymer electrolytes (GPEs) are now considered as the next-generation electrolytes to be utilized in Li-O2 systems. PVDF-HFP polymers with different lithium salts were successfully utilized as gel-polymer electrolytes to replace liquid electrolytes in Li-O2 batteries. However, the electrochemical performance of different lithium salts dissolved in PVDF-HFP matrices are limited in different aspects, i.e. (electro)chemical stability, ionic conductivity, interfacial stability, cycle stability or lithium-ion transference number. In this study, we systematically observed the effect of different lithium salts at various concentrations on the above mentioned electrochemical properties. Our results indicate that LiPF6 salt imparts best ionic conductivity into GPE systems while LiTFSI has both the widest electrochemical window and highest lithium-ion transference number. Our results indicate that the synthesis of new lithium salts having decent electrochemical performance in all aspects is of great importance in developing GPE systems.

A Bifunctional Photo-Assisted Li-O2 Battery Based on a Hierarchical Heterostructured Cathode.

Photo-assisted charging is considered an effective approach to reducing the overpotential in lithium-oxygen (Li-O2 ) batteries. However, the utilization of photoenergy during the discharge process in a Li-O2 system has been rarely reported, and the functional mechanism of such a process remains unclear. Herein, a novel bifunctional photo-assisted Li-O2 system is established by employing a hierarchical TiO2 -Fe2 O3 heterojunction, in which the photo-generated electrons and holes play key roles in reducing the overpotential in the discharging and charging processes, respectively. Moreover, the morphology of the discharge product (Li2 O2 ) can be modified via the dense surface electrons of the cathode under illumination, resulting in promoted decomposition kinetics of Li2 O2 during the charging progress. Accordingly, the output and input energies of the battery can be tuned by illumination, giving an ultralow overpotential of 0.19 V between the charge and discharge plateaus with excellent cyclic stability (retaining a round-trip efficiency of ≈86% after 100 cycles). The investigation of the bifunctional photo-assisted process presented here provides significant insight into the mechanism of the photo-assisted Li-O2 battery and addresses the overpotential bottleneck in this system.

A Comparative Study of Redox Mediators for Improved Performance of Li–Oxygen Batteries

AbstractRedox meditators (RMs) are soluble catalysts located in an electrolyte that can improve the energy efficiency (reduced overpotential) and cyclability of Li–oxygen (Li–O2) batteries. In this work, 20 RMs within a Li–O2 system with dimethyl sulfoxide and tetraethylene glycol dimethyl ether electrolytes are studied and their electrochemical features such as redox potential, the separation of cathodic and anodic peaks, and their current intensities are measured using cyclic voltammetry (CV) experiments. Six RMs are selected as “primary” choices based on their electrochemical performance, and stability tests are then performed to examine their electrochemical responses after consecutive cycles. Moreover, galvanostatic cycling tests are performed within a Li–O2 battery system assembled with selected six RMs for real case consistency investigations. It is found that results from CV to galvanostatic cycling tests are consistent for halides and organometallic RMs, where the former exhibit much higher stability. However, the organic RMs show high reversibility in CV but low in battery cycling results. Density functional theory calculations are carried out to gain more understanding of the stability and redox potentials of the RMs. This study provides comparative information to select the most reliable RMs for Li–O2 batteries along with new fundamental understanding of their electrochemical activity and stability.

Poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate)- decorated separator in Li-O2 batteries: Suppressing the shuttle effect of dual redox mediators by coulombic interactions

Although dual redox mediators (RMs) largely promote the discharge capacity and decreases the charge overpotential in Li-O2 batteries, the shuttle effect leads to a RM degradation and a serious deterioration of Li metal, which results in a poor sustainability. Here, a poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) -decorated separator has been firstly introduced into a dual mixture RMs-involved Li-O2 system, which restrains the shuttle effect via coulombic interactions. Benefiting from the advantages of as-prepared separator, a cell exhibits an enhanced cycling stability and a good reversibility associated with the Li2O2 formation and decomposition during cell cycling. These results represent a promising progress in the development of an easy-to-operate modified separator for a highly efficient Li-O2 battery.

InBr3 as a self-defensed redox mediator for Li–O2 batteries: In situ construction of a stable indium-rich composite protective layer on the Li anode

One big obstacle for a redox mediator (RM)-based Li–O2 system is the redox shuttling between the diffusible RM+ and Li anode, leading to the unexpected RM degradation and continuous deterioration of Li anode, which inevitably results in a low energy efficiency and a poor cycling stability for the Li–O2 battery. Here, InBr3 as a self-defensed RM is firstly introduced into Li–O2 batteries, which can lower the cell overpotential and thus improve the cycling performance. Moreover, due to the In3+ existence, an In-rich composite protective layer can be in situ generated on the Li anode, which contributes to suppressing the redox shuttling, improving the interface stability of Li and electrolyte, and inhibiting the dendrite formation. This work gives an insight into the development of self-defensed RM and the protection of the Li anode for Li–O2 batteries.

Molecular-Level Engineering of Protected Li Metal Anodes for High Performance Next-Generation Batteries

Li metal is a promising anode material for next-generation Li-metal battery systems due to its ultra high theoretical capacity (3860 mAh g-1) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, the instability of Li metal towards liquids electrolytes, unstable solid electrolyte interphase (SEI) formation, and dendritic lithium have caused significant safety concerns that have inhibited its commercialization [1]. It is believed that artificial SEI layers formed through various techniques can stabilize the Li metal interface and enable stable electrochemical cycling with higher Coulombic efficiency. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are nanoscale coating techniques that are capable of controlling the interfacial chemistry down to the atomic level [2]. Herein, we demonstrate the effectiveness of these techniques in enabling high performance Li metal anodes for next-generation battery systems. Various polymeric protective coatings are synthesized on Li metal by MLD to enable prolonged lifetime and cycling stability. Metalcones including Alucone and Zircone are explored and shown to greatly enhance the performance of Li-S and Li-O2 systems [3]. Moreover, the ability to fine tune the composition of artificial SEI layers is exemplified by combining ALD/MLD techniques to form hybrid organic/inorganic protection layers to further improve the stability of the Li metal anode. The performance of the protected Li metal anodes are optimized in various electrolyte systems to achieve long life times at relatively high current densities in symmetrical cells and full cells. Furthermore, a better understanding of the role of these organic/inorganic polymeric films are gained through advanced ex-situ and in-situ characterization techniques, providing insight into the mechanism of improved performance. These works display the advantages of ALD/MLD for precise interfacial engineering at the atomic/molecular level towards achieving high performance next-generation batteries. [1] Cheng, X.B.; Zhang, R.; Zhao, C.Z.; Zhang Q. Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev., 2017, 117(15), 10403-10473. [2] Meng, X.; Yang, X.Q.; Sun, X. Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater., 2012, 24(27), 3589-3615. [3] Zhao, Y.; Goncharova, L.V.; Sun, Q.; Li, X.; Lushington, A.; Wang, B.; Li, R.; Dai, F.; Cai, M.; Sun, X. Robust Metallic Lithium Anode Protection by the Molecular Layer Deposition Technique. Small Methods, 2018, 2(5), 1700417.

Transparent Conducting Oxides As Cathodes in Li-O2 batteries: A First Principles Computational Investigation

Li-O2batteries have traditionally used carbon based electrodes (graphite, buckypaper) as the cathode of choice due to its good electrical conductivity, stability against non-aqueous electrolytes like dimethoxyethane (DME) and ease of handling. But, the carbon cathode also leads to formation of carbonate by-products that increase overpotentials during charging leading to degradation of the cathode and reduction of cyclability. Recent investigations have focused on using metal-oxides like SnO2, TiO2 as viable cathodes-alternatives in Li-O2 systems. In this paper, we investigate transparent conducting oxides (TCOs) as cathodes with focus on the interface between the TCO surfaces and the discharge product, Li2O2, in the Li-O2battery using first principles computations. TCOs have found use as electrodes in photovoltaic cells and other semi-conductor applications due to their tunable conductivity via defects/doping, ease of synthesis of preferred surfaces and stability to environmental factors. These properties, along with their stability against ethers, make them a promising class of cathodes in Li-O2 battery. Using DFT computations and thermodynamic arguments, we predict the chemical and electrochemical stability of some of the well-known TCOs in a Li-O2 battery. Further, surface adsorption computations show that not all oxides promote formation of Li2O2 and different surfaces of same cathode material can behave differently. We also explore the role dopants can play in achieving a stable electrically conducting cathode that promotes discharge of Li2O2. We extend the analysis to suggest possible oxide chemistries that should be investigated as cathodes in Li-O2batteries.

Transparent Conducting Oxides as Cathodes in Li–O2 Batteries: A First Principles Computational Investigation

Li–O2 batteries have traditionally used carbon-based electrodes (graphite, buckypaper) as the cathode of choice due to their good electrical conductivity, stability against nonaqueous electrolytes like dimethoxyethane, and ease of handling. But, the carbon cathode also leads to the formation of carbonate byproducts that increase overpotentials during charging, leading to degradation of the cathode and reduction of cyclability. Recent investigations have focused on using metal oxides like SnO2, TiO2 as viable cathode alternatives in Li–O2 systems. In this paper, we investigate transparent conducting oxides (TCOs) as cathodes, with focus on the interface between the TCO surfaces and the discharge product, Li2O2, in the Li–O2 battery using first principles computations. We also explore the role dopants can play in achieving a stable electrically conducting cathode that promotes discharge of Li2O2. Our results show that attention must be paid to choosing appropriate surface of these oxides. We extend the analysis to suggest possible oxide chemistries that should be investigated as cathodes in Li–O2 batteries.

Insights into the Kinetics of Redox Mediation for Li-O2 Batteries: A Dems and RRDE Study

Due to its theoretical high specific energy Li-O2 systems have generated much interest within the electrochemical community [1]. Understanding the fundamentals of this system is import to improve it. Therefore, much effort has been put into characterizing the products and the mechanism of the underlying electrolyte systems and electrodes (also by ourselves [2-5]). Recently in the electrolyte, soluble redox mediators were proposed as additives to improve the sluggish kinetics of the oxygen reduction reaction (ORR) as well as the oxygen evolution reaction (OER)[6, 7]. Although the impact of this redox mediators is impressive, very little is known about the underlying mechanism. Therefore, we focused in this study our research in the mechanism of redox mediation of the ORR. We applied rotating ring disc technique (RRDE) as well as the differential electrochemical mass spectrometry (DEMS) to get insights into the kinetics of the mediated ORR and into the amount of consumed electrons per oxygen. The DEMS experiments were performed in a thin layer geometry without convective transport within the cell. In addition, the DEMS setup is highly sensitive to the gases formed during ORR and OER. At higher electrode potentials, the amount of evolved CO2 is reduced by adding a redox mediator to the electrolyte. We also observed that the amount of consumed oxygen is increased compared to the supporting electrolyte without redox mediator. In order to investigate the impact of the cationic charge density on the mechanism of the mediated ORR we also performed measurements in K+-, Mg2+-, Ca2+- containing electrolytes solutions. In our analysis of the data, we could calculate the share of current going into the mediation of the ORR. This analysis showed that for the investigated cations the amount of consumed electrons per oxygen molecule is 2 e-/O2. We found out, that the reaction speed of ORR could be influenced by changing the cation of the supporting electrolyte. The RRDE study revealed the generation of Li2O2 within the electrolyte volume through an analysis of the rotational dependency within the experiments. [1] K. M. Abraham and Z. Jiang, J. Electrochem. Soc., 143, 1 (1996). [2] P. Reinsberg, A. Weiss, P. P. Bawol and H. Baltruschat, J. Phys. Chem. C, 121, 7677 (2017). [3] C. J. Bondue, P. P. Bawol, A. A. Abd-El-Latif, P. Reinsberg and H. Baltruschat, J. Phys. Chem. C, 121, 8864 (2017). [4] C. Bondue, P. Reinsberg, A. A. Abd-El-Latif and H. Baltruschat, Phys. Chem. Chem. Phys., 17, 25593 (2015). [5] H. M. A. Amin, C. Molls, P. P. Bawol and H. Baltruschat, Electrochim. Acta (2017). [6] B. D. McCloskey and D. Addison, ACS Catalysis (2017). [7] X. Gao, Y. Chen, L. Johnson and P. G. Bruce, Nat. Mater., 15, 882 (2016).

Meso-pores carbon nano-tubes (CNTs) tissues-perfluorocarbons (PFCs) hybrid air-electrodes for Li-O2 battery

Adding immiscible perfluorocarbons (PFCs), possessing superior oxygen solubility and diffusivity, to a free-standing (metal-free and binder-free) CNTs air-electrode tissues with a meso-pore structure, fully maximized the advantages of PFCs as oxygenated-species' channels-providers. The discharge behavior of hybrid PFCs-CNT Li-O2 systems demonstrated a drastic increase in cell capacity at high current density (0.2 mA cm−2), where oxygen transport limitations are best illustrated. The results of this research revealed several key factors affecting PFCs-Li-O2 systems. The incorporation of PFCs with higher superoxide solubility and oxygen diffusivity, but more importantly higher PFCs/electrolyte miscibility, in a meso-pore air-electrode enabled better exploitation of PFCs potential. Consequently, the utilization of the air-electrode' surface area was enhanced via the formation of artificial three phase reaction zones with additional oxygen transportation routes, leading to uniform and intimate Li2O2 deposit at areas further away from the oxygen reservoir. Associated mechanisms are discussed along with insights into an improved Li-O2 battery system.

Oxygen Pressure Influences Spatial NaO2 Deposition and the Sudden Death Mechanism in Na–O2 Batteries

Over the past decade, metal–O2 batteries have been intensely studied as potential high energy density alternatives to current state-of-the-art Li-ion batteries. Of these, nonaqueous Na–O2 batteries offer high stability, improved full-cycle efficiency, and lower overpotentials, particularly on charge, when compared to the higher-energy-density Li–O2 system. However, Na–O2 batteries exhibit sudden and large overpotential increases or “sudden deaths” on discharge, substantially limiting the achievable capacity. In this work, we examine the influence of O2 pressure effects in Na–O2 batteries and the mechanism of sudden death at different O2 pressures and current density regimes. We observe that at a given current density, there exists a transition between failure mechanisms with O2 pressure as a result of different phenomena related to the deposition of the solid discharge product, sodium superoxide (NaO2). Cells operated at a lower O2 pressure are more susceptible to failure due to surface passivation resulting from thin NaO2 film coverage, whereas cells operated at a higher O2 pressure achieve higher capacities but are increasingly subject to failure due to pore clogging from substantial solid NaO2 deposition. We associate the transition between these failure mechanisms with a combination of electron and mass transfer effects, leading to dramatic differences in the spatial deposition of NaO2 through the cathode.

Low Cost FeCo Bimetal Cathode for Li-Air Batteries

In spite of the extremely high theoretical specific capacity of lithium oxygen (Li-O2) electrochemistry,1 low energy efficiency makes this system impractical. Among the catalysts, noble metals and their derivatives have shown improved results with low overpotentials during an oxygen evolution reaction (OER).2 Moreover, bimetal noble metal alloys have also exhibited remarkable decreases of charge overpotentials.3 However, use of noble metal based catalysts makes overcoming their inherent high cost impossible. Therefore, low cost catalysts with acceptable performance are essential for practical Li-O2 battery use. In this report, an iron cobalt bimetal-carbon nanotube (FeCo-CNT) composite was synthesized as a catalytic air cathode material for Li-O2 batteries. An Li-O2 battery using FeCo-CNT air electrodes exhibited higher efficiency than that of pristine CNT as well as higher capacity. Spectroscopic and electron microscope analyses showed that the improved cell performances can be attributed to the catalytic effect of FeCo. As a cost-effective non-noble metal catalyst, FeCo-CNT demonstrated performance comparable to noble metal catalysts in Li-O2 systems.