Li-air Cell Research Articles

A Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium-Air Batteries

Among many challenges present in Li-air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li-air cell cathodes with LiCF3SO3-TEGDME salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, since the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li2O2 formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. While Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li-air cells while maintaining electrolyte stability.

The Effect of Inorganic Nano Powder Additives in TEGDME for Lithium Air Batteries

SiO2 and Al2O3 nano llers were added to an electrolyte composed of a solution 1 M LiPF6 in tetra ethylene glycol dimethyl ether (TEGDME) and the e ects of these nano powders on capacity and cycling performances were investigated. Galvanostatic charge/discharge (GC) measurements were performed in the assembled Li-air cells by using the nanocomposite electrolytes. The discharge capacities of these cells were cyclically tested by a battery tester at a constant current in the voltage range between 2.15 V and 4.25 V. Discharge products of nanocomposite electrolytes were characterized by SEM and XRD spectroscopies. The electrochemical results demonstrated that Al2O3 reinforced electrolyte showed higher discharge capacity and cyclability than those of SiO2 reinforced electrolyte.

Reaction and degradation mechanism in all-solid-state lithium-air batteries.

The reaction and degradation mechanism in all-solid-state Li-air batteries was investigated to improve the cycling performance. It is suggested that Li2O2 is first produced by the H2O-mediated electrochemical reactions during discharging and Li2CO3 is produced by the following chemical reactions. Disruption of the CNTs and residual discharge products, which cause the capacity degradation during cycling, were observed.

A highly active nanostructured metallic oxide cathode for aprotic Li–O2batteries

A new nanostructured metallic metal oxide shows excellent ORR/OER properties in a Li–air cell, and highlights the importance of controlling the cathode interface to achieve better Li–O2cell round-trip efficiency.

Review—Understanding and Mitigating Some of the Key Factors that Limit Non-Aqueous Lithium-Air Battery Performance

In this article, we have reviewed our work on understanding and mitigating some of the key factors that limit non-aqueous Li-air battery performance. Advances in Li-air battery technology require fundamental understanding of the discharge and charge processes. We first summarize an investigation of Li-air batteries based on a well-defined cathode surfaces having size-selected silver clusters. This work provided key insight into the nucleation and growth mechanism of the discharge product and its relationship to lowering charge potentials. We then describe the development of new cathode materials including ones based on Pd and Mo2C nanoparticles that give very low charge potentials. This work has shown that it is possible to achieve very good round-trip efficiencies as well as up to 100 cycles in a Li-air cell. Finally, we discuss investigations of likely sources of electrolyte decomposition at the cathode and anode, which need to be resolved in order to achieve the long cycle life that is necessary to enable Li-air batteries.

Honeycomb-Like Perovskite Oxide Electrocatalyst for a Hybrid Li-Air Battery

Honeycomb-like Nd0.7Sr0.3CoO3−δ has been successfully prepared with a PMMA hard-template for an energy storage system and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption measurements. The prepared 3-dimensionally (3-D) ordered mesoporous Nd0.7Sr0.3CoO3−δ (3DOM-NSC) has a well-developed mesoporous structure and has high specific surface area (22.0 m2 g−1). The catalytic activity for the oxygen reduction reaction (ORR) in 0.1 M KOH solution has been studied by using a rotating-ring-disk electrode (RRDE). In the ORR test, a limiting current density of 5.83 mA cm−2 at 0.7 V (vs. Hg/HgO) with 1600 rpm was obtained, a value comparable with that of Pt/C. Moreover, the ORR mainly favors a direct four-electron pathway. Consequently, the high electrocatalytic activity and mesoporous structure result in stable, excellent performance in a hybrid Li-air cell.

Cycling Performances of Lithium-Air Cells Assembled with Mixed Electrolytes of Ionic Liquid and Diethylene Glycol Diethyl Ether

Ionic liquid-based electrolytes composed of diethylene glycol diethyl ether (DEGDEE) and 1-butyl-1-methyl pyrrolidinium bis(trifluoromethane) sulfonyl imide (BMP-TFSI) were prepared and evaluated for non-aqueous lithium-air cell applications. Adding an appropriate amount of BMP-TFSI to the electrolyte solution improved ionic conductivity, oxidative stability and interfacial stability, and reduced flammability and volatility. When BMP-TFSI was mixed with DEGDEE under optimal condition, the cycle performance was remarkably improved as compared with either the organic electrolyte or ionic liquid electrolyte alone. The Li-air cell assembled with an optimized ionic liquid-based mixed electrolyte initially delivered a high discharge capacity of 10,620 mAh g−1 and exhibited good cycling stability exceeding 150 cycles at a current density of 0.1 mA cm−2 by limiting depth of discharge to 500 mAh g−1.

Intrinsic Barrier to Electrochemically Decompose Li2CO3 and LiOH

It is widely acknowledged that Li2CO3 and LiOH as side-products in the operation of a Li–air cell should be completely removed in the cycling to avoid cumulative negative effect on the cycling performance. However, the understanding of their electrochemical decomposition is limited. We report a mechanistic analysis of the intrinsic barrier to electrochemically decompose Li2CO3 and LiOH. Our first-principles study reveals that the decomposition is rate-limited by the electrochemical extraction of Li+, whereas the chemical release of anions is barrierless once the applied voltage overcomes the energy penalty to generate a Li-deficient surface. The voltage necessary for the decomposition of Li2CO3 is predicted to be in the range of 4.38–4.61 V, whereas for LiOH it is in the range of 4.67–5.02 V. The maximum charge efficiency to decompose Li2CO3 and LiOH in the operation of a Li–air cell is estimated to be 66% and 61%, respectively. The high intrinsic barrier originates from the energy cost of oxidizing redox...

Effect of Operating Temperature in Li-Air Cells

Due to its very high value of energy density,[1] the lithium-oxygen battery has received considerable attention worldwide. Recent results have demonstrated that the battery, if operated under proper conditions, may provide acceptable values of cycle life and capacity.[2] In its most classical configuration, the Li/O2 battery is formed by a lithium metal anode, a liquid organic electrolyte and a carbon-supported (with or without catalyst) air electrode. Recently, a new configuration, where the lithium metal is replaced by a lithium alloy silicon anode, has also been reported. Key parameters in assuring proper Li/O2 battery behavior are (i) the optimization of the positive electrode structure, in terms of use of an adequate gas diffusion layer and of effective catalysts, and (ii) the choice of an electrolyte stable to superoxide attack.[2,3] It is in fact well-known that the basic electrochemical cell process, leading to the reversible formation and dissolution of lithium peroxide, involves an intermediate oxygen anion radical O2 ·-[3,4] namely, a highly reactive base that readily attacks and decomposes conventional electrolytes, such as organic carbonate solutions. Dimethoxyethane (DME)-based and ionic liquid-based solutions have been proposed as alternative electrolyte media, however with little success.Recent works demonstrated that the best results in terms of Li/O2 battery stability and cycling may be obtained with the use of long chain, ether-based glymes, such as tetraethylene glycol dimethyl ether (TEGDME) electrolyte solutions.[2] In a previous paper we have reported a detailed transmission electron microscopy (TEM) study showing that Li/O2 batteries based on the TEGDME-LiCF3SO3 electrolyte indeed show a very promising behavior at room temperature.[5] In this paper 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 ℃. 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 by measuring the TEM.

Stability Investigation of Inorganic Li Conductors As Protective Layers for Li-Air Batteries

The development of Li-air battery has received great attention recently. However, using metallic lithium directly as an anode has been challenging due to the high reactivity of Li. Protective coatings with ionic conduction on metallic Li has be proposed to overcome this problem.Inorganic Li ion conductors may be suitable for being used as the protection layer.NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 are known to be inorganic solid electrolytes with adequate conductivity in a range of 10-3 S/cm after required modification. However, Li tends to react with La0.56Li0.33TiO3 due to the incorporation of the released electrons with Ti+4 ions. Simultaneously, Li+ ions will migrate into the vacant sites in the cation sublattice. As a result, La0.50Li0.50TiO3 perovsikte becomes a mixed ionic/electronic conductor after reacting with Li. On the other hand, limited reaction was observed on the Li1+xAlxTi2-x(PO4)3 electrolyte when the metallic Li was used as the anode.In order to improve the stability of Li1+xAlxTi2-x (PO4)3, a concept of composite electrolyte based on NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 is proposed. With proper mixing and distribution of these two electrolytes, a better stability from the composite electrolyte is expected.Thus, the objective of this work is (1) to develop a composite electrolyte based on the mixture of Li1+xAlxTi2-x (PO4)3, and La0.50Li0.50TiO3, (2) to analyze the interface reaction between two components of composite cathode, (3) to investigate the electrical conduction/stability of composite as a function of volume fraction, grain size, and thickness, (4) to evaluate the feasibility of using composite electrolyte for Li-Air battery. The stability of composite electrolyte will be determined based on the measurement of the induced electronic conductivity and the open circuit voltage after a Li-air cell is assembled.

Pore-Scale Transport Resolved Model Incorporating Cathode Microstructure and Peroxide Growth in Lithium-Air Batteries

The lithium-air (Li-air) battery, shown schematically in Fig. 1, with its usable energy density close to 1,700Wh/kg has captured worldwide attention as a promising battery solution for electric vehicles. However, a major hurdle facing the development of Li-air systems is their poor round-trip efficiency owing to the formation of electrically insulating lithium peroxide (Li2O2) at the cathode surface. Although it is well known that Li2O2 inhibits the reduction process during cell charging, how the deposition morphology of Li2O2 affects the cell performance is poorly understood. Ex-situ imaging has shown that the Li-air cathodes have highly intricate structures and the deposition of Li2O2 is equally complex. However, all existing simulations thus far treat the electrode/Li2O2 matrix as a homogenous continuum and utilize simply-shaped electrode morphologies, such as spheres and rods, to construct volume-averaged expressions (see Fig. 2a) for porosity and surface area. The formation of Li2O2 is then modeled as growing uniformly above these simplified electrodes, and manifests merely as a change in bulk porosity. Such assumptions are insufficient in characterizing the precise effect of the complex electrode/Li2O2microstructure on cell performance. In this paper, we present a pore-scale transport resolved model (see Fig. 2b) of the Li-air battery that fully accounts for the electrode microstructure and peroxide growth. This approach requires no empirical correlations regarding the electrode morphology. Additionally, the growth of Li2O2 is modeled locally and no longer requires the assumption of uniform deposition. Utilizing this pore-scale transport resolved model, the complex electrode and Li2O2 morphologies can be directly incorporated into the numerical model and their effects on system-level performance can be evaluated. Incorporating the thickness-dependent electron resistivity and rate-dependent growth morphology of Li2O2, results obtained from our pore-scale model agree well with experiments. The validated model is then used to predict the galvanostatic discharge behavior of a Li-air cell for a variety of electrode/Li2O2 morphologies. The effects of pore-size (e.g., macro-, meso-, and micro-pores), electrode structure, discharge/charge rate, and oxygen solubility on Li2O2 growth and cell performance are presented. Figure 3 shows the cell voltage versus specific capacity curves for electrodes with different microstructures. The model presented here will be a valuable tool for rational design of electrode microstructures for improved cell performance.

Invited: Novel Cell Design and Inexpensive Electrocatalysts for Hybrid Lithium-Air Batteries

Growing environmental concerns and increasing demand for energy have stimulated extensive interest in electrical energy storage, particularly in the form of batteries. Li-air batteries are appealing in this regard as they offer much higher energy density than the current Li-ion batteries. However, the nonaqueous Li-air batteries are hampered by electrolyte degradation and clogging of the air electrodes by the insoluble discharge products. Interestingly, hybrid Li-air batteries in which a solid electrolyte separates the lithium metal anode in an aprotic electrolyte from the air electrode in an aqueous catholyte could overcome these problems. However, there are many challeges that need to be overcome, e.g.,poor stability of the solid electrolyte in strongly acidic or alkaline catholytes, high internal resistance, and lack of less expensive, efficient, durable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts. Much effort has been focused on developing efficient bifunctionl catalysts to lower the overpotential and improve the stability of hybrid Li-air batteries in recent years, but the cycle life is still limited. This presentation will focus on advanced cell configurations and high-performance catalysts for hybrid lithium-air batteries.We have developed an advanced hybrid Li-air cell with decoupled, mesoporous nanocatalysts, which could be cycled for over 100 cycles (400 hours) in air with only 0.08 V increase in round-trip overpotential based on discharge and charge end voltages. With this cell configuration, mesoporous NiCo2O4 nanoflakes directly grown onto a nickel foam (NCONF@Ni) serve as the OER electrode. The catalytic active surface area increased from < 1 m2 g-1 for nickel foam to more than 80 m2 g-1. The spinel NiCo2O4 catalyst exhibits much higher catalytic activity and stability than Ni metal at high potentials, leading to a fairly low OER overpotential that is comparable to that seen with the noble-metal IrO2 catalyst. A nitrogen-doped mesoporous carbon (NMC) with extremely high surface area (1520 m2 g-1) and optimized nitrogen doping content (3.9 wt. %) was loaded onto a hydrophobic carbon fiber paper to act as the ORR electrode. The highly mesoporous NMC exhibits activity similar to the noble-metal Pt/C catalyst, but with much better stability. With this configuration, a variety of other non-noble-metal or metal-free catalysts could play the role of ORR without worrying about their stability in the high-voltage charge process. For example, we have developed a 3-D O- and N-doped carbon nanoweb as a highly active metal-free catalyst for ORR in hybrid Li-air cells. The 3-D nanoweb structure provides an ideal backbone support for catalytically active sites due to the fast electron and mass transport properties compared with the 1-D or 2-D structure. In addition, the synergistic effect between the O and N groups creates highly active pyridone groups all over the nanoweb surface, which significantly improves the catalytic activity toward ORR. Furthermore, a phosphate buffer catholyte with a moderate pH has been developed to protect the solid electrolyte in hybrid Li-air batteries. It contains phosphoric acid and supporting salts, which reduce the internal resistance and overpotential. A high energy density could be achieved by utilizing all three protons in phosphoric acid. Further increase in power density and efficiency has also been realized by increasing the solid-electrolyte conductivity and the operating temperature to 40 oC.

Electrochemical performance of surface modified CNF/Co3O4 composite for Li-air batteries

This article describes the electrochemical performance of an air electrode employing a CNF/Co3O4 composite. A polydopamine layer was coated on the surface of the composite to increase its wettability toward the electrolyte used. In addition, a dissolved catalyst (LiI) was introduced to facilitate the dissociation of reaction products. The polydopamine-coated CNF/Co3O4 composite showed better charge capacity and cyclic performance than a pristine CNF/Co3O4 composite. Moreover, the use of LiI effectively decreased the overpotential and increased the cyclic performance of Li-air cells. Thus, the combined use of a polydopamine-coated CNF/Co3O4 composite and a dissolved catalyst (LiI) was very effective for enhancing the electrochemical properties of Li-air cells.

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.

Stability Enhancement of Nasicon Solid Electrolytes As Protective Layer for Li-Air Systems

The development of Li-air battery has received great attention recently. However, using metallic lithium directly as as an anode has been challenging due to the high reactivity of Li. Protective coatings with ionic conduction on metallic Li has be proposed to solve this problem.Inorganic Li ion conductors may be suitable for using as the protection layer.NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 are known to be inorganic solid electrolytes with adequate conductivity in a range of 10-3 S/cm after required modification. However, Li tends to react with La0.56Li0.33TiO3 due to the incorporation of the released electrons with Ti+4 ions. Simultaneously, Li+ ions will migrate into the vacant sites in the cation sublattice. As a result, La0.50Li0.50TiO3 perovsikte becomes a mixed ionic/electronic conductor after reacting with Li. On the other hand, limited reaction was observed on the Li1+xAlxTi2-x(PO4)3 electrolyte when the metallic Li was used as the anode.In order to improve the stability of Li1+xAlxTi2-x (PO4)3, a concept of composite electrolyte based on NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 is proposed. With proper mixing and distribution of these two electrolytes, a better stabiltiy from the composite electrolyte is expected.Thus, the objective of this work is (1) to develop a composite electrolyte based on the mixture of Li1+xAlxTi2-x (PO4)3, and La0.50Li0.50TiO3, (2) to analyze the interface reaction between two components of composite cathode, (3) to investigate the electrical conduction/stability of composite as a function of volume fraction, grain size, and thickness, (4) to evaluate the feasibility of using composite electrolyte for Li-Air battery. The stability of composite electrolyte will be determined based on the measurement of the induced electronic conductivity and the open circuit voltage after a Li-air cell is assembled.

Development of a High Temperature PEO-Based Li-O2 Battery

Li-air battery has the potential of becoming the ultimate power source among all electrochemical energy conversion and storage configurations derived from lithium chemistry. Unfortunately, current configurations, mostly based on a non-aqueous organic liquid electrolyte, suffer from numerous challenges, namely high electrolyte volatility, electrolyte decomposition, low cycle-life, low discharge rates and high discharge/charge over-potential. A very appealing Li-air configuration is obviously one which sees the use of a solid, solvent-free, electrolyte, such as those formed by combining poly(ethylene oxide), PEO, and a lithium salt. Polymer electrolytes are well known promising materials for high energy density rechargeable batteries. Polymer electrolytes poses several advantages over liquid based electrolytes systems, in terms of high chemical, thermal and electrochemical stabilities, all of those are important factors for batteries in number of applications, ranging from portable electronics to electric vehicles. However, wide use of solid polymer electrolyte is still prevented by the decay in ionic conductivity (10-7 to 10-5 S cm-1 at room temperature), resulting from low ionic mobility, high degree of polymer matrix crystallinity, and low degree of charge separation in addition to ion association. We hereby offer a new Li-air battery configuration, based on the well-investigated PEO- lithium salt electrolyte system. The Li-air battery will be comprised of a lithium metal anode, a highly Li+ conductive, oxygen permeable PEO-based, lithium polymer electrolyte and a high surface area carbon air cathode. As opposed to current lithium polymer electrolytes, which operate at room temperature and suffer from low ionic conductivity, the new proposed configuration will operate at a high temperature of 80°c. Above 70°c PEO predominantly exists in the amorphous state, thus a practically useful conductivity is easily achievable in the temperature range of 70-95°c. Our Li-air cell is discharged/ charged at high temperature, thus enabling better kinetics, resulting in high current densities and lower over-potential. The system is studied by electrochemical methods as well as spectroscopic ones.The results of this work will contribute to the development of practically viable Li-air batteries.

Invited Presentation: Striving Toward an Ultrahigh Energy Density Li-Air Battery

In the pursuit to develop a practical rechargeable Li/air battery, we have studied the mechanisms of O2 reduction and evolution reactions (ORR and OER), and the nature of the products formed, in a series of organic electrolytes and ionic liquids. The distinct ORR products formed in these disparate electrolyte solutions can be explained using a general theory based on the Hard Soft Acid Base (HSAB) concept. We have found that the electron donor property of the solvent modulates Li+ acidity in organic electrolytes , through the formation of complexes (or solvates) of the formula Li(solvent)n + where, n = 2-4, and these solvates in turn influence the mechanisms and products of both catalyzed and uncatalyzed ORR in Li-air batteries. A cobalt phthalocyanine-derived catalyst has enabled the full reduction of O2 to Li2O in selected solvents, and provided improved rechargeability for Li-air cells. Acknowledgment: The US Army US Army RDECOM CERDEC C2D, Aberdeen Proving Grounds, MD, provided financial support for this work Dr. K. M. Abraham is Professor at Northeastern University Center for Renewable Energy Technology, Boston, Massachusetts, USA. KM has made many pioneering contributions to advance primary and secondary lithium and Li-ion batteries including the invention of the lithium-air battery.

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.

Suppression of Unwanted Reactions on the Carbon-Based Air Electrode

In the past decade, lithium ion batteries have played a dominant power source for items ranging from portable electronics to hybrid electric vehicles. However, they still do not offer enough energy density to meet the ever-increasing demands of many applications despite extensive research to explore ways to increase their charge-storage capability. As a new energy storage system, Li-air batteries have attracted numerous attentions because they have the potential to provide several times higher capacity than commercial Li-ion cells [1-2]. Li-air batteries have been developed in different types according to the electrolytes employed, such as aqueous, non-aqueous, and hybrid systems. Because of relatively simple configuration and large real capacity, non-aqueous system is most active all Li-air batteries. Much research effort has been devoted in order to enhance the performance of Non-aqueous Li-air cells [3-4]. However, they still are facing fundamental and practical challenges such as low rate capability, limited cycle life resulting from the instability of the electrode and electrolyte, and significant overpotential on charge due to slow kinetics of dissociation from reaction products (such as Li2O2). These critical issues are highly attributed to the air electrode, the reaction place between lithium ion and oxygen, and electrolyte directly contact with electrode. In this study, the suppression of unwanted reactions on the air electrode during cycling is main issue. With aim to suppress the unwanted reactions, the surface of carbon was passivated by stable materials. The surface defects of carbon facilitate unwanted electrolyte decomposition reactions during cycling, which deteriorate the cyclic performance of air cell [5-6]. So the passivation of carbon is expected as an effective approach for enhancing the cycling performance of the Li-air batteries.

Free-standing flexible graphene oxide paper electrode for rechargeable Li–O2 batteries

A smooth, free-standing and flexible graphene oxide paper was produced using a vacuum filtration technique. This graphene oxide paper was characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy techniques. The charge–discharge characteristics of the graphene oxide paper have been investigated from 1 V to 4.5 V at a constant 0.01 mA cm−2 with an ECC–Air test cell. The electrochemical impedance of the graphene oxide paper has been measured to investigate the difference in the resistance of the cell before and after an electrochemical cycling test. The Li–air cell with a graphene oxide flexible paper cathode exhibited a 612 mAh g−1 discharge capacity and a 555 mAh g−1 charge capacity after 10 cycles. This study demonstrated that graphene oxide paper might be a good alternative cathode material for Li–O2 batteries in the future.