Decomposition Of Li2O2 Research Articles

Nanogravel structured NiO/Ni foam as electrode for high-performance lithium-ion batteries

Nanogravel structured NiO/Ni electrodes were fabricated by using two-step thermal oxidation method of commercial nickel (Ni) foam in air for lithium-ion batteries (LIBs). The macro- and micro-structures of the NiO/Ni foam were characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), and Raman spectroscopy. Galvanostatic tests revealed that the electrode exhibits no obvious capacity fading over 40 cycles at 1 C (718 mAg−1) and 2.5 C (1.8 Ag−1) current rate. The discharge capacity was higher than the theoretical capacity of NiO even at a high-current rate of 2.5 C. The electrodes can deliver a reversible capacity of 1116.65 mAh g−1 after 20th cycle at 1 C rate and 1026.20 mAh g−1 after 40th cycle at 2.5 C rate. The cyclic voltammograms and impedance spectra analysis indicated that a redox reaction of NiO–Ni0 with formation and decomposition of Li2O. The excellent electrochemical performance is mainly attributed to the nanogravel structure of the NiO/Ni foam electrodes as well as its excellent electrical contact between NiO and Ni. The unique nanostructured NiO on the highly conductive metallic Ni in core resulted in the enhanced discharge capacity, coulombic efficiency, cyclic stability, and rate capability when utilized as negative electrodes in LIBs.

CeO2 Nanoparticle-Guided Formation and Decomposition of Amorphous Li2O2 on Carbon Nanotube Cathode in a Li-O2 Cell

The structure and morphology of lithium peroxide (Li2O2) in a lithium-oxygen (Li-O2) cell have been widely explored by their correlation to recharge potential. A toroidal Li2O2 crystal with 0.1-1 μm size is a typical and predominant product observed on various carbonaceous cathodes after the 1st discharge (2Li + O2 ↔ Li2O2)1 while the bulk size and poor conductivity of Li2O2 incurs its sluggish decomposition during the recharge, which results in a rapid potential rise more than 4.2 V vs. Li/Li+ concomitant with severe side reactions. This potential shooting can be suppressed by some conductive additives such as metal and metal oxide nanoparticles (NPs), where non-crystalline and/or thin Li2O2 is interestingly observed after discharge. For example, our previous work demonstrated less 4.0 V of potential for the whole recharge process in the presence of RuO2 NPs that led to the formation of amorphous Li2O2 film on the carbon nanotube (CNT) cathode during discharge via its high O2 adsorption affinity.2 Therefore, it is considered that the physical property of Li2O2, arising from both the poor crystallinity having higher ionic and electronic conductivity3 and the thin-film shape providing large contact area with the CNT cathode,4 is beneficial to smooth decomposition of Li2O2 at low potential. However, the criteria for promising additives contributing to the structure and morphology engineering of Li2O2 and mechanistic study for the formation and decomposition of such a unique structure of Li2O2 have not as yet been conducted. Here we present in-depth study of nucleation, growth and decomposition process of non-crystalline Li2O2 in the presence of cerium oxide (CeO2) NPs using TEM and correlate this to Li-O2 cell performance. The small diameter of CeO2 NP (~5 nm) has strong affinity for the oxygen species (O2, O2 - and O2 2-),5-6 which is accordingly a good candidate to investigate the evolution of Li2O2 morphology during discharge and recharge. At initial discharge, the nucleation of Li2O2 appears on the CeO2 NPs, but not on the CNT, from which the Li2O2 laterally grows and coats over the CNT surface. The CeO2 NPs determine the height of Li2O2 film, thus thicker Li2O2 film can be observed in the area of agglomerative CeO2 NPs. Further discharge allows a vertical growth (i.e. thicker film) once the thin Li2O2 film covers the entire CNT surface. There is no evidence of Li2O2 crystal structure, which is very distinguished from the toroidal and polycrystalline Li2O2 observed on a CeO2-free CNT (Fig. 1). The decomposition of Li2O2 seems to emerge from the amorphous and thin Li2O2 surface, which results in low recharge potential at the initial stage. However, the CeO2 NPs having strong O2 and CO2 affinity7 and poor conductivity become a hurdle for the completion of Li2O2 decomposition at low potential unlike the RuO2 NPs. The implication of CeO2 role and characteristics of the unique structure of Li2O2 based on different discharge and recharge status will be discussed in details in the presentation.

Solution Phase Catalysts for Lithium-Oxygen Batteries

A lithium-oxygen battery (LOB) would deliver the highest energy density of a rechargeable battery. But there is a central problem of catalytic action required for the rechargeable LOB: conventional solid state catalysts are not effective enough to catalyze the multiphase electrochemical reactions on the cathode side. The discharge product Li2O2 is also in solid state; it will accumulate at the catalyst surface and hence block the electrode reactions during the discharge process. Meanwhile, during the charging process, it is also difficult to make good contact between the solid catalyst and Li2O2. Therefore, instead of solid catalysts, some novel solution phase catalysts have been developed to solve the above problems1-3. Here, we present a solution-phase catalyst, iron phthalocyanine (FePc), and provide a mechanism involving iron-oxygen coordination and a redox shuttle across the electrolyte4. The Fe-oxygen coordination and the electron dislocation in the big conjugated structure lowers the energy of the high energy intermediates in the ORR and OER. The dissolved FePc can act as a molecular shuttle of (O2)− species and electrons between the surface of electronically conducting carbon and product Li2O2 particles. With this novel approach, the formation and decomposition of Li2O2 is no longer confined to the carbon surface. The Li2O2blocking effect in the discharge process was greatly depressed. Meanwhile, the redox shuttle mechanism effectively lowers the overpotential during the charging process. Thus, the capacity and cyclability of the battery was improved dramatically. Some other solution phase catalysts based on the redox shuttle mechanism, such as ferrocene-derived compounds and iodine, will also be discussed. The efficiency of various redox couples to oxidize the Li2O2during charging is compared with an oxygen monitoring method. We also show some evidence of side reactions caused by some certain redox shuttle compounds. Reference: (1) Y.H. Chen, S.A. Freunberger, Z.Q. Peng, O. Fontaine & P.G. Bruce, "Charging a Li-O-2 battery using a redox mediator". Nat. Chem., 2013, 5(6),489-494. (2) H.-D. Lim, H. Song, J. Kim, H. Gwon, Y. Bae, K.-Y. Park, J. Hong, H. Kim, T. Kim, Y.H. Kim, X. Lepró, R. Ovalle-Robles, R.H. Baughman & K. Kang, "Superior Rechargeability and Efficiency of Lithium–Oxygen Batteries: Hierarchical Air Electrode Architecture Combined with a Soluble Catalyst". Angewandte Chemie International Edition, 2014, 53(15),3926-3931. (3) B.J. Bergner, A. Schurmann, K. Peppler, A. Garsuch & J. Janek, "TEMPO: A Mobile Catalyst for Rechargeable Li-O2 Batteries". J. Am. Chem. Soc., 2014, 136(42),15054-15064. (4) D. Sun, Y. Shen, W. Zhang, L. Yu, Z. Yi, W. Yin, D. Wang, Y. Huang, J. Wang, D. Wang & J.B. Goodenough, "A Solution-Phase Bifunctional Catalyst for Lithium–Oxygen Batteries". J. Am. Chem. Soc., 2014, 136(25),8941-8946.

Interfacial redox reaction-directed synthesis of silver@cerium oxide core–shell nanocomposites as catalysts for rechargeable lithium–air batteries

A facile oxidation–reduction reaction method has been implemented to prepare pomegranate-like Ag@CeO2 multicore–shell structured nanocomposites. Under Ar atmosphere, redox reaction automatically occurs between AgNO3 and Ce(NO3)3 in an alkaline solution, where Ag+ is reduced to Ag nanopartilces and Ce3+ is simultaneously oxidized to form CeO2, followed by the self-assembly to form the pomegranate-like multicore–shell structured Ag@CeO2 nanocomposites driven by thermodynamic equilibrium. No other organic amines or surfactants are utilized in the whole reaction system and only NaOH instead of organic reducing agent is used to prevent the introduction of a secondary reducing byproduct. The as-obtained pomegranate-like Ag@CeO2 multicore–shell structured nanocomposites have been characterized as electro-catalysts for the air cathode of lithium–air batteries operated in a simulated air environment. Superior electrochemical performance with high discharge capacity of 3415 mAh g−1 at 100 mA g−1, stable cycling and small charge/discharge polarization voltage is achieved, which is much better than that of the CeO2 or simple mixture of CeO2 and Ag. The enhanced properties can be primarily attributed to the synergy effect between the Ag core and the CeO2 shell resulting from the unique pomegranate-like multicore–shell nanostructures possessing plenty of active sites to promote the facile formation and decomposition of Li2O2.

Designed hybrid nanostructure with catalytic effect: beyond the theoretical capacity of SnO2 anode material for lithium ion batteries.

Transition metal cobalt (Co) nanoparticle was designed as catalyst to promote the conversion reaction of Sn to SnO2 during the delithiation process which is deemed as an irreversible reaction. The designed nanocomposite, named as SnO2/Co3O4/reduced-graphene-oxide (rGO), was synthesized by a simple two-step method composed of hydrothermal (1st step) and solvothermal (2nd step) synthesis processes. Compared to the pristine SnO2/rGO and SnO2/Co3O4 electrodes, SnO2/Co3O4/rGO nanocomposites exhibit significantly enhanced electrochemical performance as the anode material of lithium-ion batteries (LIBs). The SnO2/Co3O4/rGO nanocomposites can deliver high specific capacities of 1038 and 712 mAh g−1 at the current densities of 100 and 1000 mA g−1, respectively. In addition, the SnO2/Co3O4/rGO nanocomposites also exhibit 641 mAh g−1 at a high current density of 1000 mA g−1 after 900 cycles, indicating an ultra-long cycling stability under high current density. Through ex-situ TEM analysis, the excellent electrochemical performance was attributed to the catalytic effect of Co nanoparticles to promote the conversion of Sn to SnO2 and the decomposition of Li2O during the delithiation process. Based on the results, herein we propose a new method in employing the catalyst to increase the capacity of alloying-dealloying type anode material to beyond its theoretical value and enhance the electrochemical performance.

Mesoporous NiO with a single-crystalline structure utilized as a noble metal-free catalyst for non-aqueous Li–O2 batteries

Porous-structured NiO nanosheets, synthesized by means of a facile alcohol-thermal method, were utilized as a noble metal free catalyst for non-aqueous Li–O2 batteries. The NiO showed good activity for the decomposition of Li2O2 and Li2CO3.

Capillary based Li–air batteries for in situ synchrotron X-ray powder diffraction studies

A novel design for in situ X-ray diffraction Li–O2 battery reveals the crystallographic details for the precipitation and decomposition of Li2O2 for the 1st and 2nd cycles of the battery.

Unraveling the Catalytic Mechanism of Co3O4 for the Oxygen Evolution Reaction in a Li–O2 Battery

Unraveling the catalytic mechanism of transition-metal oxides (TMOs) for the charging reaction in a Li–O2 battery and characterizing their surface structures and electronic structure properties of active sites are of great importance for the development of an effective catalyst to improve low round-trip efficiency and power density. In the current study, an interfacial model is first constructed to study the decomposition reaction mechanism of Li2O2 supported on Co3O4 surfaces. The computational results indicate that the O-rich Co3O4 (111)C with a relatively low surface energy in high O2 concentration has a high catalytic activity in reducing overpotential and O2 desorption barrier due to the electron transfer from the Li2O2 layer to the underlying surface. Meanwhile, the basic sites of Co3O4 (110)B surface induce Li2O2 decomposition into Li2O and a dangling Co–O bond, which further leads to a high charging voltage in the subsequent cycles. The calculations for transition-metal (TM)-doped Co3O4 (111) indi...

Pt/α-MnO2 nanotube: A highly active electrocatalyst for Li–O2 battery

The preparation of α-MnO2 nanotubes (M-NT) decorated with platinum nanoparticles (Pt/M-NT) by a simple reduction and mechanical stirring method is presented in this work, which aims to design a highly active catalyst for the Li–O2 battery. The obtained samples were characterized by XRD, SEM, TEM, BET, and XPS techniques. The electrocatalytic performance of the prepared samples was evaluated by tracking the decomposition of Li2O2 during the charging process in a Li-O2 cell using in situ XRD and operando SR-PXD, which gave direct and time resolved information during the whole process. The results indicated that Pt nanoparticles were uniformly dispersed on the surface of M-NT. Even a small amount (1wt%) of Pt on M-NT did largely enhance the kinetics of the charging process. A cell with 5wt% Pt/M-NT showed the highest catalytic activity and lowest charging potential. The decomposition of Li2O2 during the charging process in a Li–O2 cell with 5wt% Pt/M-NT followed a zero-order reaction. This promoting effect from the supported nanocatalyst can be attributed to the high surface area, highly dispersed and uniform Pt deposition, and proper surface state modifications.

Carbon Nanotube‐Encapsulated Noble Metal Nanoparticle Hybrid as a Cathode Material for Li‐Oxygen Batteries

Although Li‐oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end‐opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT‐encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li2O2 nanocrystals on CNT surfaces instead of localized distribution of Li2O2 aggregation, thus providing efficient charge transfer for the decomposition of Li2O2.

First Principles Study of Lithium and Oxygen Adsorption on the β-MnO2 (110) Surface

The Li-air system is a novel battery technology which promises higher specific energy than Li-ion batteries. In this battery the cathode reaction is not the formation of an intercalation compound but the reduction of oxygen gas in the presence of Li+ ions forming lithium peroxide Li2O2 (or LiOH in the aqueous version).1-5 Manganese oxides may also play an important role in this battery: it has been shown that nanostructured MnO2 in different polymorphic states are able to catalyse the formation and decomposition of Li2O2 in the cathode. Understanding the behaviour of the cathode catalysts is the key for improving the function of Li-air batteries.6 The adsorption and co-adsorption of lithium and oxygen at the surface of rutile-like manganese dioxide (β-MnO2), which are important in the context of Li-air batteries, are investigated using density functional theory. In the absence of lithium, the most stable surface of β-MnO2, the (110), adsorbs oxygen in the form of peroxo groups bridging between two manganese cations. Conversely, in the absence of excess oxygen, lithium atoms adsorb on the (110) surface at two different sites, which are both tri-coordinated to surface oxygen anions, and the adsorption always involves the transfer of one electron from the adatom to one of the five-coordinated manganese cations at the surface, creating (formally) Li+ and Mn3+ species. The co-adsorption of lithium and oxygen leads to the formation of a surface oxide, involving the dissociation of the O2 molecule, where the O adatoms saturate the coordination of surface Mn cations and also bind to the Li adatoms. This process is energetically more favourable than the formation of gas-phase lithium peroxide (Li2O2) monomers, but less favourable than the formation of Li2O2 bulk. These results suggest that the presence of β-MnO2 in the cathode of a non-aqueous Li-O2battery lowers the energy for the initial reduction of oxygen during cell discharge.1. M. Armand and J. M. Tarascon, Nature, 2008, 451, 652-657.2. P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature materials, 2011, 11, 19-29.3. K. Abraham and Z. Jiang, Journal of The Electrochemical Society, 1996, 143, 1-5.4. R. Black, B. Adams and L. Nazar, Advanced Energy Materials, 2012, 2, 801-815.5. J. Christensen, P. Albertus, R. S. Sanchez-Carrera, T. Lohmann, B. Kozinsky, R. Liedtke, J.Ahmed and A. Kojic, Journal of The Electrochemical Society, 2011, 159, R1-R30.6. Y. Shao, S. Park, J. Xiao, J.-G. Zhang, Y. Wang and J. Liu, ACS Catalysis, 2012, 2, 844-857.

In-Situ Observation of Li-O2 Electrochemical Reactions Using Electrochemical AFM

Despite outstanding gravimetric energy density of a nonaqueous lithium-oxygen (Li–O2) battery in regard to promising future energy storage, a true Li–O2 electrochemical reaction has not been deeply understood. In particular, a little knowledge of dynamic Li–O2 process of formation, growth and decomposition of Li2O2 has been known. Here, we present in–situ imaging of the Li–O2 electrochemical reactions using atomic force microscopy (AFM) coupled with electrochemical tester.[1,2] A highly oriented pyrolytic graphite (HOPG) and metallic lithium were employed to working and counter/reference electrodes, respectively, which were fully immersed in O2 gas-saturated tetraethylene glycol dimethyl ether (tetraglyme) containing 0.5 M of LiTFSI (LiN(SO2CF3)2). Cyclic voltammetry was carried out at a potential range of 2.0-4.5 V with a scanning of HOPG surface by an insulating AFM tip in an Ar-filled glove box, which offered almost identical condition to the actual Li-O2 cell. In addition, the AFM tip scanning for imaging did not significantly disturb the growth/decomposition process of Li2O2. Upon the oxygen reduction reaction (ORR), the nucleation of nanoparticle (diameter = 3–10 nm) was observed at the step edge of HOPG. These nanoparticles grew up to a diameter of 200 nm and migrated to the terrace of HOPG. When the potential approached to 2.0 V, new morphology products having rectangular and elongated nanoplates were rapidly formed at the edge of HOPG, which became predominant products for further reduction, thus constructing a thick Li2O2 film, demonstrated by X-ray photoelectron spectroscopy (XPS). Interestingly, the size of Li2O2 nanoplates on the top surface of Li2O2 film was much smaller than the one on the HOPG, which was probably attributed to slow charge transport according to growth of thick Li2O2 film having the poor electronic conductivity. The Li2O2 was decomposed upon oxygen evolution reaction (OER), where the thick and dense Li2O2 film delayed its decomposition and demanded for higher oxidation potential compared to the thin and low density of Li2O2. For control experiments, we replaced the ether-based electrolyte and HOPG electrode with carbonate and nanoporous gold, and also extended the voltammetry cycling number. These conditions provided different morphology of products and chemical identifications, which would be discussed in the presentation.

Chemical Instability of Dimethyl Sulfoxide in Lithium-Air Batteries.

Although dimethyl sulfoxide (DMSO) has emerged as a promising solvent for Li-air batteries, enabling reversible oxygen reduction and evolution (2Li + O2 ⇔ Li2O2), DMSO is well known to react with superoxide-like species, which are intermediates in the Li-O2 reaction, and LiOH has been detected upon discharge in addition to Li2O2. Here we show that toroidal Li2O2 particles formed upon discharge gradually convert into flake-like LiOH particles upon prolonged exposure to a DMSO-based electrolyte, and the amount of LiOH detectable increases with increasing rest time in the electrolyte. Such time-dependent electrode changes upon and after discharge are not typically monitored and can explain vastly different amounts of Li2O2 and LiOH reported in oxygen cathodes discharged in DMSO-based electrolytes. The formation of LiOH is attributable to the chemical reactivity of DMSO with Li2O2 and superoxide-like species, which is supported by our findings that commercial Li2O2 powder can decompose DMSO to DMSO2, and that the presence of KO2 accelerates both DMSO decomposition and conversion of Li2O2 into LiOH.

Nitrogen-doped carbon nanotubes with hydrazine treatment as cathode materials for lithium-oxygen batteries

Nitrogen-doped multi-wall carbon nanotubes (N-MWCNTs) were obtained by hydrazine reflux treatment. The introduction of hydrazine leads to successful nitrogen insertion in the form of mostly pyrrolic N. Meanwhile, the intrinsic characteristics of carbon nanotubes were retained. In addition, the N-MWCNTs exhibited superior electrochemical performance to that of pristine multi-wall carbon nanotubes (MWCNTs). The prepared N-MWCNTs delivered an initial discharge capacity of 2,927 mAh g−1 at a current density of 0.05 mA cm−2 and presented better reversibility especially at high rate and better electrocatalytic activity than MWCNTs. The results revealed that nitrogen doping into MWCNTs facilitated the reduction of oxygen and it was beneficial for Li2O2 decomposition as well.

The Influence of Electrolyte Salt and Solvent on the Morphology of Li2O2 Formed on Li-Air Cathodes

Li-air batteries are an exciting class of energy storage devices with exceptional theoretical capacities which could facilitate longer-range electrical vehicles if fully optimised systems are realised.1 Energy storage in Li-air batteries proceeds via different mechanisms to those associated with conventional Li-ion batteries, necessitating detailed studies into the fundamental processes associated with discharge and charge. Recently, increasing attention has been devoted to understanding the role of the electrolyte in determining the performance of Li-air batteries. It has been conclusively shown that carbonate based electrolytes are not suitable for rechargeable systems due to the rapid accumulation of carbonate based species on the cathode.2 These carbonates are particularly prevalent during the charging process due to decomposition of the electrolyte and reactions between the electrolyte, the primary discharge product Li2O2 and its intermediates. Numerous reports have revealed that characteristic Li2O2 toroids often form on the cathode surface during discharge in a variety of cathode/electrolyte systems.3 , 4 Recently, Nazar et al. showed that the formation of these toroids is strongly related to the applied current for a given system (TEGDME/LiTFSI electrolyte and Super P carbon cathode).5 Their results show that at low applied currents, large crystalline Li2O2 toroids form on the cathode surface with a clear change to quasi-amorphous Li2O2 films at higher applied currents. They also found that the toroids were much more difficult to decompose during charge than the thin films, indicating that the nature of the Li2O2formed on discharge plays a key role in determining rechargeability.In this work we have investigated the morphology and composition of discharge products formed on Super P cathodes using various different electrolyte solvent and salt combinations. We demonstrate that even at high applied currents (250 μA), electrolytes containing sulfolane as the electrolyte solvent show preferential Li2O2 toroid formation (Figure 1 a,b). In comparison, electrolytes using TEGDME (Figure 1 c,d) as the electrolyte solvent do not lead to the formation of Li2O2 toroids at the same applied currents. The comparative performance of cells using the various electrolytes determined using galvanostatic charge-discharge methods were demonstrated to be linked to the morphology and areal coverage of the Li2O2 formed on the cathodes. The decomposition of these particles and films is visualized by conducting ex-situ SEM analysis at various stages of the charge process. The influence of catalyst addition (Pd, MnO2, Co3O4) to Super P carbon cathodes on the morphology of Li2O2 formed on cathodes and thus their electrochemical performance was also probed. This report gives insight into the importance of understanding the formation and decomposition of Li2O2 on cathodes for realizing rechargeable high capacity Li-O2 battery systems. Figure 1: SEM images of Super P cathodes discharged with an applied current of 250 μA using different electrolyte solvent/salt combinations.1. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Nature materials 2011,11, (1), 19-29.2. McCloskey, B. D.; Bethune, D. S.; Shelby, R. M.; Girishkumar, G.; Luntz, A. C. The Journal of Physical Chemistry Letters 2011,2, (10), 1161-1166.3. Fan, W.; Cui, Z.; Guo, X. The Journal of Physical Chemistry C 2013. 117 (6), pp 2623–26274. Mitchell, R. R.; Gallant, B. M.; Shao-Horn, Y.; Thompson, C. V. The Journal of Physical Chemistry Letters 2013, 1060-1064.5. Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Energy & Environmental Science 2013,6, (6), 1772-1778. Acknowledgements: Financial support was provided by the European Union Seventh Framework Programme (FP7/2007-2013) project STABLE.

Influence of Gold Nanoparticles Anchored to Carbon Nanotubes on Formation and Decomposition of Li2O2 in Nonaqueous Li–O2 Batteries

Gold nanoparticles (AuNPs) anchored to vertically aligned carbon nanotubes (VACNTs) act as additional nucleation sites for the Li2O2 growth, leading to the decreased size while increased density of Li2O2 particles in process of discharge. Correspondingly, at the deep discharge to 2.0 V the batteries show increased specific capacity. Upon charge, the AuNPs exhibit promotion effect on the Li2O2 decomposition by improving the conduction property of the discharge-formed particles, rather than by imposing the conventional electrocatalytic effect on the oxygen evolution reaction. Moreover, the AuNPs show promotion effect on decomposition of carbonate species arising from the side reactions. These effects consequently lead to the reduced charge overpotentials and extended cycle operation of the batteries. The results here provide a new as well as clear picture on the role of incorporated AuNPs in the Li2O2 formation and decomposition, which would be helpful for better understanding and constructing of high-perfo...

Behind Extended Cycling of Li-O2 Battery

New battery technologies are demanded for a growing market of electric and hybrid vehicles. Rechargeable Li-O2 batteries are promising candidates for this application because of their high theoretical energy density. Although high capacity values are achievable for Li-O2batteries, their cycling stability is typically limited by only a few full discharge-charge cycles. On the other hand, good cycling behavior under limited capacity conditions has been reported by several groups.Rechargeability of Li-O2 batteries is based on the reversible formation/oxidation of Li2O2. Unfortunately, the electrochemical processes of oxygen reduction and evolution are harmful for commonly used carbon-based electrodes and organic electrolytes causing severe decompositions. Generation and continuous accumulation of insulating side products on the electrode/electrolyte interface results in increasing polarization and fast capacity fading with cycling.In the present report we demonstrate that long cycle life of Li-O2 batteries is in principle achievable upon selection of appropriate carbon material and catalyst for air cathode fabrication in addition to a proper cycling protocol (Fig. 1a). The origin of the extended cycling is in efficient decomposition of both Li2O2 and side products during the charging step of the battery operation. Extended cycling of a Li-O2 battery was investigated by quantification of Li2O2 yield during discharge and O2 release during charging. There is a drastic shift from the predominant formation of Li2O2 to the predominant formation of carbonate- and carboxylate-containing side products within first few cycles followed by a stabilization of Li2O2 yield. Mass spectroscopy of gasses evolved during the corresponding charging steps demonstrate drop in oxygen release and increase in CO2release in the very beginning of battery cycling (Fig. 1b).Drastic switch to the formation of side products in the beginning of battery cycling originates from certain changes on the electrode/electrolyte interface as was analyzed with X-ray photoelectron spectroscopy. In addition, morphological considerations and cycling conditions to achieve unrestricted cycling of Li-O2battery will be discussed in the presentation. Acknowledgement This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U. S. Department of Energy (DOE). The microscopic analysis in this work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences.Figure 1. a) Voltage profiles and b) in situ MS analysis of O2 and CO2 evolved during charging of the battery with CNTs/Ru electrodes cycled in TEGDME-LiTf electrolyte.

Facile and Cost Effective Synthesized Mesoporous Spinel NiCo2O4 as Catalyst for Non-Aqueous Lithium-Oxygen Batteries

The electrochemical performance of lithium-oxygen batteries can be significantly improved by employing a suitable catalyst to enhance the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a versatile, effective and economic co-precipitation synthesis of spinel NiCo2O4 with an urchin-like structure has been reported as an electrocatalyst for rechargeable non-aqueous Li-O2 batteries. The spherical urchin-like structure of spinel NiCo2O4 was formed without the use of any template or surfactant. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics in the Li-O2 batteries could be drastically improved by employing the effective NiCo2O4 catalyst, achieving a higher discharge potential and rate. In particular, the urchin-like structure of the catalyst not only provides more electrocatalytic sites but also promotes mass transport in the electrolyte. In addition, mesoporous NiCo2O4 can efficiently catalyze the formation and decomposition of Li2O2. The Li-O2 battery containing the urchin-like NiCo2O4 catalyst exhibited the highest specific capacity of about 7309 mA h g−1 at 0.2 mA cm−2. The integrity and porosity of spinel NiCo2O4 had a significant effect on the performance of the Li-O2 battery with reasonable specific capacity and cyclability, suggesting that the NiCo2O4-based materials can be effective catalysts for oxygen electrode in high performance Li-O2 batteries.

Accelerated Electrochemical Decomposition of Li2O2 under X-ray Illumination

This work presents the first report detailing the effect of X-rays on the electrochemical decomposition of Li2O2, which is the main reaction during the charging process in a Li–O2 battery. An operando synchrotron radiation powder X-ray diffraction (SR-PXD) experiment was performed. The results indicate that the electrochemical decomposition of Li2O2 is dramatically accelerated under X-ray irradiation. The accelerated decomposition of Li2O2 follows a zero-order reaction, and the decomposition rate constant is proportional to the intensity of X-ray used. A mechanism for the electrochemical decomposition of Li2O2 under X-ray irradiation is proposed. These results give an insight into the charging process in Li–O2 batteries.

A Facile Mechanism for Recharging Li2O2 in Li–O2 Batteries

Li–air is a novel battery technology with the potential to offer very high specific energy, but which currently suffers from a large charging overpotential and low power density. In this work, we use ab initio calculations to demonstrate that a facile mechanism for recharging Li2O2 exists. Rather than the direct decomposition pathway of Li2O2 into Li and O2 suggested by equilibrium thermodynamics, we find an alternative reaction pathway based on topotactic delithiation of Li2O2 to form off-stoichiometric Li2–xO2 compounds akin to the charging mechanism in typical Li-ion intercalation electrodes. The low formation energy of bulk Li2–xO2 phases confirms that this topotactic delithiation mechanism is rendered accessible at relatively small overpotentials of ∼0.3–0.4 V and is likely to be kinetically favored over Li2O2 decomposition. Our findings indicate that at the Li2O2 particle level there are no obstacles to increase the current density, and point to an exciting opportunity to create fast charging Li–air...