Lithium Oxygen Cells Research Articles

Highly Reversible Redox of Oxygen-Peroxide Couple on Carbon-Based Electrode in Aqueous Media

Introduction Lithium-oxygen battery is the most promising battery system owing to its high theoretical energy density. The biggest challenges in the lithium-oxygen battery is the very high overpotential >1V, which limits the power density of the cell in the case of the non-aqueous electrolyte. On the other hand, since aqueous lithium oxygen battery shows much lower overpotential even under high current density, we think the aqueous system should be suitable for high power applications such as EV or HEV. Basically the reaction mechanism of the aqueous lithium-oxygen battery has been explained in the following four-electron transfer reaction. O2 + H2O +4e- ↔ 4OH-E=3.446 V vs. LiIt is known that the actual cathodic reduction process of the oxygen occurs by two two-electron steps described in the following equations in alkaline solution [1]. 1st stage: O2 + H2O + 2e- → HO2 - + OH- 2nd stage: HO2 - + H2O + 2e- → 3OH- Since the kinetics of the second stage of the reaction is significantly dependent upon the catalytic activity of the electrode materials, a lot of studies for the oxygen reduction catalyst such as platinum, gold, palladium, rhodium and so forth, were carried out for fuel cell applications. On the other hand, Yager et al. reported that the 2nd stage of the reaction does not occur on the carbon-based electrode because of its poor catalytic activity of carbon [2]. Furthermore they also reported that the 1ststage of the reaction based on the oxygen-peroxide couple is highly reversible on the carbon-based electrode. In the present study we attempted to utilize the reversible electrochemical reaction of the oxygen-peroxide couple on the carbon-based electrode as the positive electrode reaction of the lithium-oxygen battery. Experimental A gas diffusion electrode used in this study consists of two layers of carbon based electrode layer. As a reaction layer of the electrode, Ketjen black and PTFE was mixed in the mortar and pestle and pressed into a uniform sheet. The prepared sheet was punched and layered with a carbon paper used as a diffusion layer. A three-electrode electrochemical cell consists of the above gas-diffusion electrode as the working electrode, a Pt/Pt black electrode as the counter electrode and a Ag/AgCl electrode as the reference electrode was prepared for the fundamental electrochemical study of the oxygen peroxide couple. An aqueous electrolyte solution was prepared by dissolving 10 M of LiCl and saturated LiOH·H2O. A 5 wt. % of H2O2 solution (30wt%) was added into the solution to form HO2 -in the solution. The lithium-oxygen cell was prepared in nitrogen atmosphere and operated in oxygen atmosphere to avoid the contamination of CO2, which forms non-active Li2CO3. Results and Discussion Fig. 1 shows the cyclic voltammograms of the lithium-oxygen cell with / without H2O2 in the electrolyte. The electrolyte containing H2O2 showed clear reversibility with very negligible overpotential while the H2O2-free electrolyte showed approximately 0.4 V of overpotential. Furthermore the H2O2 containing electrolyte showed much higher current even with low polarization. The result suggests that the reversibility of the oxygen peroxide couple is significantly dependent upon the activity of HO2 -ion in the electrolyte solution. Detailed electrochemical properties associated with the electrolyte design will be discussed in the presentation. Reference [1] James Patrick Hoare, The Electrochemistry of Oxygen, Chapter IV, Interscience Publishers, Inc. (1968)[2] E. Yeager, P. Krouse and K.V. Rao, Electrochimica Acta, 9 (1964) 1057-1070

Reactivity of Amide Based Solutions in Lithium–Oxygen Cells

The stability of electrolyte solutions during lithium–oxygen cells operation is of great importance and interest. This is because oxides formed during reduction are strong nucleophiles which can initiate solvent decomposition. The highly polar amide based solvents have come to the fore as possible candidates for Li–O2 applications. They show typical cycling behavior as compared to other solvents; however, their stability toward lithium oxides is shrouded in doubt. The present study has focused on Li–O2 cells containing electrolyte solutions based on DMA/LiNO3. We have used various analytical tools, to explore the discharge–charge processes and related side reactions. The data obtained from FTIR, NMR, XPS, and EQCM all support a rational decomposition mechanism. The formation of various side products during the course the first discharge, leads to the conclusion that amide based solvents are not suitable for Li–O2 applications; however, electrolyte solution decomposition reduces the OER overpotential by forming oxidation mediators.

Surface Enhanced Raman Microscopy in the Study of Li-Ion and Li-Air Battery Interfaces

Surface layers on lithium battery electrodes play a vital role in affecting battery performance, ageing mechanics and safety. Particularly, the solid electrolyte interphase (SEI), which is a protecting layer formed on the negative electrode of lithium-ion batteries as a result of electrolyte decomposition, significantly impacts upon irreversible charge “loss”, rate capability, cyclability, exfoliation of graphite and safety.The investigation of surface layer formation is also important in the understanding of the operation of the lithium-oxygen battery. The non-aqueous lithium-oxygen cell is one of a host of emerging opportunities available for enhanced energy storage [1]. Unlike a conventional battery where the reagents are contained within the cell, the lithium-oxygen cell uses dioxygen from the atmosphere to electrochemically form the discharge product lithium peroxide. Degrees of reversible oxidation and formation of lithium peroxide has been demonstrated in a number of non-aqueous electrolyte classes, mostly notably in dimethysulfoxide based electrolytes [2], thus making the lithium-oxygen cell a potential energy storage device.The design and optimisation of techniques based on both surface-enhanced Raman spectroscopy (SERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) for ultra-sensitive analysis will be presented in the study the formation and composition of interfaces on lithium battery electrode materials. SHINERS, first reported by Prof. Tian and his co-workers [3] provides, as does SERS, an ultra-sensitive technique for understanding the formation and composition of interphases/ passivation layers on electrode materials and is considered to be a powerful technique for in situ surface analysis. The highest enhancement of Raman scattering using SHINERS appears at the junction between the particles and substrate as hot spots with magnitudes of up to 4x108 fold. Raman signals can be greatly enhanced by surface plasmon resonance generated on the surface of gold or silver nanoparticles. In SHINERS, the gold nanoparticles are coated with ultrathin silica or alumina layer. The inert shell is expected to be thin, uniform, fully enclosed and optically transparent so that it can retain the surface enhancement and ensure that there is no direct contact between the probed substance and the gold core. The shell-isolated nanoparticles are then spread onto the electrode surface and assembled into an in situ Raman electrochemical cell.The poster will present our groups recent results of the spectro-electrochemistry studies of dioxygen in non-aqueous electrolytes, as well the use of SHINERS to understand model electrode interfaces within Li-ion battery electrolytes.

Toward a Lithium-‘air’ Battery: The Effect of CO2 on the Chemistry of a Lithium-Oxygen Cell

Lithium-oxygen chemistry offers the highest energy density for a rechargeable system; such a system is known as a “lithium-air battery”. Most studies of lithium-air batteries have focused on demonstrating battery operations in an environment of pure oxygen; such a battery should technically be described as a “lithium-dioxygen (O2) battery”. Consequently, the next step for the lithium-“air” battery is to understand how the reaction chemistry is affected by the constituents of ambient air. Among the components of air, CO2 is of particular interest because its solubility in organic solvents is about fifty times higher than that of O2, and it can react actively with O2 - ·, which is the key intermediate species in Li-O2 battery reactions. In this work, we investigated the reaction mechanisms in the Li-O2/CO2 cell under various electrolyte conditions using quantum mechanical simulations combined with experimental verification. Our most important finding is that the subtle balance among various reaction pathways influencing the potential energy surfaces can be modified by the electrolyte solvation effect. Thus, a low dielectric electrolyte tends to primarily form Li2O2, while a high dielectric electrolyte is effective in electrochemically activating CO2, yielding only Li2CO3. Most surprisingly, we further discovered that a high dielectric medium such as DMSO can result in the reversible reaction of Li2CO3 within a Li-air cell (contrary to conventional belief) over multiple cycles. We believe that the current mechanistic understanding of the chemistry of CO2 in a Li-air cell and the interplay of CO2 with electrolyte solvation will provide an important guideline for developing Li-air batteries. Furthermore, the newly discovered possibility for a rechargeable Li-O2/CO2 battery based on Li2CO3 formation chemistry may have merits in enhancing cyclability by minimizing side reactions.

Invited Presentation: Air Batteries with Ionic Liquid Electrolytes: The Abile Project

Electrification has been a major focus of BMW and large efforts have been initiated in order to investigate technologies of high potential to be integrated in future electric vehicles. Metal-air and particularly lithium-air batteries [1] are one of the possible solutions that may substantially enhance the electric drive range. The main challenges in Li-air batteries are related to the stability of the electrolyte and safety of the negative electrode. BMW, together with three scientific teams initiated a project focusing on the use of ionic liquids and alternative anodes as potential components for Li-air batteries.Due to their excellent electrochemical and chemical properties, onium-based ionic liquids [2] were chosen as the first candidates. The presentation will describe the electrochemical behaviour of a Li-air cell comprising such ionic liquid-based electrolytes. The results prove the concept that the chosen ionic liquid may assure the proper lithium-oxygen cell operation and electrochemical stability during cycling.In this presentation work towards system safety improvement will be also shown [3]. In this field, alternatives to the lithium metal anode were investigated. The latter include: i) tin-carbon composite, ii) carbon-coated Zn1-xFexO [4], iii) SiOx-carbon and SiOx-silicon materials. Electrochemical tests have shown reversible behaviour of all materials both in conventional organic electrolytes as well as in electrolytes based on ionic liquids.

Deactivation of carbon electrode for elimination of carbon dioxide evolution from rechargeable lithium-oxygen cells.

Carbon has unfaired advantages in material properties to be used as electrodes. It offers a low cost, light weight cathode that minimizes the loss in specific energy of lithium-oxygen batteries as well. To date, however, carbon dioxide evolution has been an unavoidable event during the operation of non-aqueous lithium-oxygen batteries with carbon electrodes, due to the reactivity of carbon against self-decomposition and catalytic decomposition of electrolyte. Here we report a simple but potent approach to eliminate carbon dioxide evolution by using an ionic solvate of dimethoxyethane and lithium nitrate. We show that the solvate leads to deactivation of the carbon against parasitic reactions by electrochemical doping of nitrogen into carbon. This work demonstrates that one could take full advantage of carbon by mitigating the undesired activity.

In Situ Spectroscopic Studies of the Electrochemistry of Dioxygen in Non-Aqueous Li-Air Battery Electrolytes

The non-aqueous lithium-oxygen battery is one of a host of emerging opportunities available for enhanced energy storage [1]. Unlike a conventional battery where the reagents are contained within the cell, the lithium-oxygen cell uses dioxygen from the atmosphere to electrochemically form the discharge product lithium peroxide. Degrees of reversible oxidation and formation of lithium peroxide has been demonstrated in a number of non-aqueous electrolyte classes, mostly notably in dimethysulfoxide based electrolytes [2], thus making the lithium-oxygen cell a potential energy storage device. A schematic representation of the rechargeable non-aqueous Li-O2 cell is shown in the Figure. On discharge, lithium ions formed at the lithium metal anode are transported across the electrolyte and into the pores of the air-cathode. O2 from the atmosphere enters the cathode, and dissolves into the electrolyte within the pores. It is then reduced at the porous carbon electrode surface by electrons from the external circuit and combines with Li+ from the electrolyte, leading to the formation of solid Li2O2 as the final discharge product. Surprisingly, the reaction in some electrolytes is fairly reversible, Li2O2 can be oxidised, releasing oxygen gas. The challenge for the Li-O2 cell is the progress of development of the air-cathode that allows highly reversible formation of Li2O2 in a stable electrolyte within its pores [3-6]. This talk will present our groups recent results of the electrochemistry of dioxygen in non-aqueous electrolytes on planar and single crystal electrodes, of which particular electrolytes could have practical application within a lithium-oxygen cell. Discussion will touch upon how the electrochemistry can be related to electrode substrate and will be presented with in situ spectroscopic studies that identify intermediate and surface species during the oxygen reduction reaction.P.G. Bruce, S. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nature Mater. (2012) 11 19Z. Peng, S.A. Freunberger, Y. Chen, P.G. Bruce, Science, (2012) 337 563S. Freunberger, Y. Chen, N. Drewett, L.J. Hardwick, F. Bardé, P.G. Bruce, Angew. Chem. Int. Ed. (2011) 50 8609S. Freunberger, Y. Chen, Z. Peng, J. Griffin, L.J. Hardwick, F. Bardé, P. Novák, P.G. Bruce, J. Amer. Chem. Soc. (2011) 133 8040Z. Peng, S. Freunberger, L.J. Hardwick, Y. Chen, V. Giordani, F. Bardé, P. Novák, J.-M. Tarascon, D. Graham, P.G. Bruce, Angew. Chem. Int. Ed. (2011) 50 63514M. Leskes, N Drewett, L.J. Hardwick, P.G. Bruce, G.R. Goward, C.P. Grey, Angew. Chem. Int. Ed. (2012) 51 8560

Comparisons of heat treatment on the electrochemical performance of different carbons for lithium-oxygen cells

Lithium-oxygen (Li-O2) cells are a promising power source, and carbons are an attractive non-metal catalyst for air electrodes. To improve the electrochemical performance, various carbons are heated in an inert atmosphere. It is found that heat treatment at 900°C can differently improve the electrochemical performance of multiwalled carbon nanotubes (CNTs), acetylene carbon black (AB) and activated carbon (AC), but the improvement of CNTs is the most obvious. After heat treatment, the peak current density of the oxygen reduction reaction (ORR) and the 1st discharge capacity of CNTs increase ∼30% and ∼125%, respectively, while the charge transfer reaction resistance and the Warburg diffusion resistance decrease ∼7.0% and ∼11.1%, respectively. AC has the highest charge capacities and capacity retention ratio in spite of little influence by heat treatment. The possible mechanism and reasons are analyzed using different techniques. Microstructure is superior to conductivity for enhancing the rechargeability and the cyclability, and heat treatment is effective for some carbon materials in improving the electrochemical performance of Li-O2 cells.

Role of the Lithium Salt in the Performance of Lithium–Oxygen Batteries: A Comparative Study

AbstractIn this paper we report a comparative study of the electrochemical properties of a lithium–oxygen cell using a tetraethylene glycol dimethyl ether (TEGDME)‐based electrolyte solution with four different lithium salts, namely, lithium‐bis‐(trifluormethanesulfonyl)‐imide, LiN(SO2CF3)2, lithium trifluoromethanesulfonate, LiCF3SO3, lithium perchlorate, LiClO4, and lithium hexafluorophosphate, LiPF6. This study evidences the role of the electrolyte salt in affecting the cell polarization as a reflection of its specific properties in terms of lithium transference number and interface resistance. LiCF3SO3 is finally identified as the best choice for assuring low cell polarization.

Improved cycle efficiency of lithium metal electrodes in Li–O2 batteries by a two-dimensionally ordered nanoporous separator

We demonstrate a facile but very effective approach to improve the cycling efficiency of metallic lithium electrodes by controlling the pore morphology of separators. We employed anodized porous alumina as the model nanoporous separator and demonstrated the improvement of cycle efficiency of lithium electrodes in lithium–oxygen cells.

Nanosized Carbon‐Supported Manganese Oxide Phases as Lithium–Oxygen Battery Cathode Catalysts

AbstractThe poor discharge and recharge efficiency demonstrated by lithium–air batteries renders the search for highly active and inexpensive oxygen reduction and evolution catalysts crucial to the development of these energy‐storage and conversion devices. Previous works have shown that manganese oxides are promising lithium–oxygen cathode catalysts, which is in agreement with their remarkable activities for the reduction and evolution of oxygen in aqueous media. Motivated by these resembling catalytic behaviors, we prepared and characterized a number of manganese oxide modifications directly on carbon black and attempted to correlate their oxygen reduction and evolution activities in aprotic and aqueous electrolytes. Although our results cannot confirm this correlation, they provide valuable insight into the reaction mechanisms at play in each medium. More precisely, in 0.1 M potassium hydroxide, the reduction of oxygen is related to the reduction of a manganese(III) intermediate whereas the oxidation of hydrogen peroxide (which was regarded as a mimic of the lithium peroxide produced upon lithium–oxygen battery discharge) correlates with the transition between manganese(II) and manganese(III) phases. In the aprotic medium, manganese oxide cathodes prefilled with lithium peroxide showed a strong catalytic effect but were not active in the oxidation of lithium peroxide produced in the previous discharge. This discrepancy is thought to arise from the stark differences in the sizes and morphologies of the lithium peroxide involved in each test, which implies that the catalytic activity of a material for the oxidation of lithium peroxide prefilled on electrodes is not indicative of its behavior in the charging of a real lithium–oxygen cell.

Investigation of the carbon electrode changes during lithium oxygen cell operation in a tetraglyme-based electrolyte

In this paper we investigate in details the changes occurring in the lithium–oxygen cell during operation in a tetraglyme-base electrolyte, in terms of electrochemical behavior and of carbon electrode morphology. The study evidences a decrease of the cell polarization and impedance during cycling associated with a morphological change of the carbon electrode, as demonstrated by SEM images. We attribute the change of the electrode morphology to the already known carbon oxidation process, here resulting in an increased porosity favoring the reversible electrochemical process. The results here reported shed light on important aspects to be considered in order to better understand the complex behavior of the lithium–oxygen battery.

Influence of Temperature on Lithium–Oxygen Battery Behavior

In this Letter we report an electrochemical and morphological study of the response of lithium-oxygen cells cycled at various temperatures, that is, ranging from -10 to 70 °C. The results show that the electrochemical process of the cells is thermally influenced in an opposite way, that is, by a rate decrease, due to a reduced diffusion of the lithium ions from the electrolyte to the electrode interface, at low temperature and a rate enhancement, due to the decreased electrolyte viscosity and consequent increased oxygen mobility, at high temperature. In addition, we show that the temperature also influences the crystallinity of lithium peroxide, namely of the product formed during cell discharge.

Magnetism in Lithium–Oxygen Discharge Product

Nonaqueous lithium-oxygen batteries have a much superior theoretical gravimetric energy density compared to conventional lithium-ion batteries, and thus could render long-range electric vehicles a reality. A molecular-level understanding of the reversible formation of lithium peroxide in these batteries, the properties of major/minor discharge products, and the stability of the nonaqueous electrolytes is required to achieve successful lithium-oxygen batteries. We demonstrate that the major discharge product formed in the lithium-oxygen cell, lithium peroxide, exhibits a magnetic moment. These results are based on dc-magnetization measurements and a lithium-oxygen cell containing an ether-based electrolyte. The results are unexpected because bulk lithium peroxide has a significant band gap. Density functional calculations predict that superoxide-type surface oxygen groups with unpaired electrons exist on stoichiometric lithium peroxide crystalline surfaces and on nanoparticle surfaces; these computational results are consistent with the magnetic measurement of the discharged lithium peroxide product as well as EPR measurements on commercial lithium peroxide. The presence of superoxide-type surface oxygen groups with spin can play a role in the reversible formation and decomposition of lithium peroxide as well as the reversible formation and decomposition of electrolyte molecules.

Investigation of a Li-O2 cell featuring a binder-free cathode via impedance spectroscopy and equivalent circuit model analysis

Many studies of the discharge performance of traditional lithium oxygen (Li-O2) cells with binder also include electrochemical impedance spectroscopy (EIS) data and equivalent circuit models (ECM) to provide additional insight on the electrochemical kinetics driving cell operation. However, no EIS and ECM data have been reported for binder-free Li-O2 cells. In this work, EIS and ECM data are analyzed and first reported for a binder-free Li-O2 cell. The EIS results are consistent with the overall discharge capacity results for a cell that is experiencing increased polarization due to cycling, and the fitted equivalent circuit accurately models the same behavior. Surface morphology is also presented for the cell and exhibits product formation on the cathode that is consistent with increased polarization.

Mesoporous Nitrogen‐Doped Carbon‐LiSICON Glass Ceramics as High Performance Cathodes in Solid‐State Lithium–Oxygen Batteries

Power trip! A new composite cathode for lithium–oxygen batteries is developed by using a highly mesoporous nitrogen-doped carbon blend and 20 wt % lithium aluminum germanium phosphate. This composite exhibits excellent electrochemical activity for oxygen reduction. The lithium–oxygen cell performance is an order of magnitude higher than that of cells with cathodes fabricated by using only carbon.

Lithium–oxygen cells with ionic-liquid-based electrolytes and vertically aligned carbon nanotube cathodes

Cycle performance of Li–O2 cells with N-methyl-N-propylpiperidinium bis(trifluoromethansulfony)imide (PP13TFSI)–LiClO4 electrolytes and vertically aligned carbon nanotube (VACNT) cathodes has been investigated. It is found that both the current density and the depth of discharge have great influence on the capacity utilization, voltage polarization and cycle life. Abacus-ball-shaped Li2O2 particles produced at discharge are identified, and their complete decomposition at charge is confirmed. Meanwhile, formation of Li carbonates around the VACNTs is detected after the first cycle. The carbonates accumulate and gradually become predominant over Li2O2 upon cycling, leading to decrease of the discharge capacity and increase of the cell resistance. These results indicate that reduction of the carbonates formed around the VACNTs is of critical importance for improving cycle performance of the cells investigated here.

Functional binder for high-performance Li–O2 batteries

In the present work, the polypyrrole (PPy), as a conductive polymer, is for the first time introduced as functional binder of air cathode for lithium–oxygen batteries by a self-assembly process. Most of the carbon particles in the air cathode are found to be uniformly congregated with each other by the in-situ polymerized conductive polymer PPy, which affords a lower electrode resistance and higher electrode integrity. Replacement of the conventional inactive PVDF binder by the functional conductive polymer in the cathode, which not only acts as the binder and conductor, but also functions as a host for fast Li-ion insertion/extraction, has demonstrated its effectiveness in improving the cycle-efficiency, specific capacity, rate capability and cycling stability of the lithium–oxygen cells. In comparison with the PVDF binder, the PPy/C cathode demonstrates ∼2.6 times (2626.3 mA h g−1vs. 1005.8 mA h g−1) and ∼5.3 times (1816.4 mA h g−1vs. 345.6 mA h g−1) higher capacity at 0.1 mA cm−2 and 0.5 mA cm−2 respectively.

A comprehensive study on the cell chemistry of the sodium superoxide (NaO2) battery

This work reports on the cell chemistry of a room temperature sodium-oxygen battery using an electrolyte of diethylene glycol dimethyl ether (diglyme) and sodium trifluoromethanesulfonate (NaSO3CF3, sodium triflate). Different from lithium-oxygen cells, where lithium peroxide is found as the discharge product, sodium superoxide (NaO2) is formed in the present cell, with overpotentials as low as 100 mV during charging. Several analytical methods are used to follow the cell reaction during discharge and charge. Changes in structure and morphology are studied by SEM and XRD. It is found that NaO2 grows as cubic particles with feed sizes in the range of 10-50 μm; upon recharge the particles consecutively decompose. Pressure monitoring during galvanostatic cycling shows that the coulombic efficiency (e(-)/O2) for discharge and charge is approx. 1.0, the expected value for NaO2 formation. Also optical spectroscopy is identified as a convenient and useful tool to follow the discharge-charge process. The maximum discharge capacity is found to be limited by oxygen transport within the electrolyte soaked carbon fiber cathode and pore blocking near the oxygen interface is observed. Finally electrolyte decomposition and sodium dendrite growth are identified as possible reasons for the limited capacity retention of the cell. The occurrence of undesired side reactions is analyzed by DEMS measurements during cycling as well as by post mortem XPS investigations.

The Role of Catalysts and Peroxide Oxidation in Lithium–Oxygen Batteries

A promotor for lithium batteries: nanocrystalline cobalt(II,III) oxide supported on graphene enhances the transport kinetics for both oxygen reduction and oxygen evolution in the lithium-oxygen cell. On cycling the lithium-oxygen cell, the effect of the promoter is, however, eventually overwhelmed by side reactions in the cell, such as, the deposition of carbonates.