Performance Of Li-O2 Batteries Research Articles

Impact of Cathodic Electric Double Layer Composition on the Performance of Aprotic Li-O2 Batteries

One of the difficulties limiting the development of high capacity Li-O2 batteries is the positive electrode passivation by the discharge product Li2O2 which is deposited mostly due to the second electron transfer of oxygen reductionwhich requires the presence of Li+ in the Stern layer. To suppress the passivation and shift the reaction zone of Li2O2 formation towards the electrolyte bulk, we propose to use additional cations in the electrolyte. Using molecular dynamics simulations, we investigate the ability of various cations to replace Li+ ions in the first cation layers near the electrode, with EMI+ (1-ethyl-3-methylimidazolium) and PP13+ (N-methyl-N-propylpiperidinium) showing pronounced effects. However, our experimental studies including cycling voltammetry and discharge capacity measurements in high and low donor number solvents reveal practically no effect of such addition. Therefore, Li+ should be fully eliminated from electron transfer zone, and this is possible by anchoring of additional cations according to the simulations. We optimized the surface density for these cations, although the experimental support of this approach looks challenging.

Phosphorus-doped carbon as cathode material for high energy nonaqueous Li-O2 batteries

Porous carbon materials are usually employed as cathode catalysts in Li-O2 batteries. However, the poor catalytic performance of carbon cathode often results in low capacity and severe overpotential. Herein, we successfully prepared phosphorus doped carbon material by one-step pyrolyzation, effectively improving the performance of Li-O2 batteries. The discharge capacity of Li-O2 battery with P doped carbon reaches 3400 m Ah g−1 at 200 mA g−1, which is increased by 52% compared to the un-doped sample. Besides, greatly decreased discharge overpotential and enhanced rate capability are also obtained after phosphorus doping. Furtherly, phosphorus doping was found to crucially affect the growth of discharge products, and the solution driven mechanism becomes more prominent, leading to larger sized discharge products and prolonged battery life. Our work provides a new way of improving the catalytic performance of carbon cathode for Li-O2 batteries.

Fe2O3 nanorods decorated with ultrafine CeO2 as binder-free cathode to improve the performance of Li-O2 batteries

The rechargeable Li-O2 batteries have attracted considerable attention in recent years because of their high theoretical energy density. However, the development of Li-O2 batteries is hampered due to the poor cycling performance and high discharge/charge overpotential. In this work, we developed a unique composite of CeO2-decorated Fe2O3 nanorods supported on carbon cloth (Fe2O3/CeO2@CC) as binder-free cathode catalyst. The Fe2O3/CeO2@CC significantly reduced overpotentials for oxygen redox reactions. And their battery could perform to 94 cycles (at 340 mA/g with a limited capacity of 500 mAh/g), which is much better than that of Fe2O3@CC-catalyzed battery (64 cycles). Such well performances should result from that CeO2 catalyst also could serve as oxygen buffer. CeO2 could supply oxygen under deficient conditions and remove oxygen under rich conditions, reducing the interference of oxygen concentration to the battery.

Electrode Protection in High-Efficiency Li-O2 Batteries.

The aprotic Li–O2 battery possessing the highest theoretical energy density, approaching that of gasoline, has been regarded as one of the most promising successors to Li-ion batteries. Before this kind of battery can become a viable technology, a series of critical issues need to be conquered, like low round-trip efficiency and short cycling lifetime, which are closely related to the continuous parasitic processes happening at the cathode and anode during cycling. With an aim to promote the practical application of Li–O2 batteries, great effort has been devoted to identify the reasons for oxygen and lithium electrodes degradation and provide guidelines to overcome them. Thus, the stability of cathode and anode has been improved a lot in the past decade, which in turn significantly boosts the electrochemical performances of Li–O2 batteries. Here, an overlook on the electrode protection in high-efficiency Li–O2 batteries is presented by providing first the challenges of electrodes facing and then the effectiveness of the existing approaches that have been proposed to alleviate these. Moreover, new battery systems and perspectives of the viable near-future strategies for rational configuration and balance of the electrodes are also pointed out. This Outlook deepens our understanding of the electrodes in Li–O2 batteries and offers opportunities for the realization of high performance and long-term durability of Li–O2 batteries.

Role of Discharge-Product Morphology and Formation Rates in Li–O2 Battery Performance

Lithium–oxygen batteries have unprecedented theoretical capacity. Achieving the theoretical capacity in practice remains a challenge – even during low-power operation – because of higher-order phenomena that accompany the formation of discharge products, such as surface passivation and clogging of the cathode’s pores. In the last few years, Li–O2 battery research has moved towards systems that preferentially form large discharge-product particles, which can be achieved by using high-donicity electrolytes and including mediators as additives.1 In this study we examine the implications of discharge-product growth and morphology on performance using numerical simulations.A continuum model is developed which incorporates multicomponent mass transfer2 described by Onsager-Stefan-Maxwell laws. Including more details about liquid-phase transport is particularly important when modelling solution-mediated discharge processes, because the diffusion of soluble reaction intermediates can control the battery’s apparent discharge capacity. Detailed reaction models, which include precipitation and film-growth kinetics are also necessary, to elucidate the competition between discharge-product formation pathways3: thin-film formation can slow interfacial reaction kinetics, whereas pore clogging raises overpotentials by hindering the transport of reactive species.Large discharge products form through a solution-phase mechanism, which is favoured by electrolytes that sustain the presence of an LiO2 intermediate for a relatively long time. These intermediate forms the final Li2O2 discharge product either by electrochemically reacting with a lithium ion or by chemically disproportionating, thereby contributing to discharge-product-particle growth. When LiO2 reaction intermediates are long-lived, they can build up in the electrolyte, particularly near the electrode/electrolyte interface. Thus, the system is locally pushed from the dilute into the concentrated regime, and pairwise interactions between species can become significant to device performance.(1) Torayev, A.; Magusin, P. C. M. M.; Grey, C. P.; Merlet, C.; Franco, A. A. Text Mining Assisted Review of the Literature on Li-O2 Batteries . J. Phys. Mater. 2019, 2, 044004.(2) Liu, J.; Khaleghi Rahimian, S.; Monroe, C. W. Capacity-Limiting Mechanisms in Li/O2 batteries. Phys. Chem. Chem. Phys. 2016, 18, 22840–22851.(3) Yin, Y.; Torayev, A.; Gaya, C.; Mammeri, Y.; Franco, A. A. Linking the Performances of Li–O2 Batteries to Discharge Rate and Electrode and Electrolyte Properties through the Nucleation Mechanism of Li 2 O 2. J. Phys. Chem. C 2017, 121, 19577–19585.

Study on the Effect of Surface Area on the ORR Performance of Perovskite Catalyst for High Performance Lithium-Oxygen Batteries

Lithium oxygen(Li-O2) batteries have been recognized as one of the next-generation power sources, capable of supplying power for a long time even in an independent extreme environment. In spite of the theoretical advantage, Li-O2 batteries face technical and economical challenges that must be addressed to promote them as commercially variable techcologies for future energy system. Above all, battery performance largely depends on the activities of the cathode during discharge and charge, respectively. The undesirable overpotential caused by sluggish reaction kinetics assiciated with the ORR and OER greatly limit the current performance of Li-O2 batteries, which must be improved by efficient catalyzing the reactions. Among the numerous catalysts, perovskite oxides have attention for candidate electrocatalyst for Li-O2 batteries due to their high electronic/ionic conductivity, high electrochemical stability, and catalytic activity. Especially, La0.6Sr0.4Co0.2Fe0.8O3(LSCF) is considered as a typical catalyst for Li-O2 batteries, which and provide high oxygen surface exchange coefficient for fast kinetics at the gas/electrode interface. The surface area is significantly related on the ORR and OER performance, which influences on the active area for reactions. In this study, we have tried to utilize a simple high energy ball milling process to investigate the electrochemical properties of LSCF catalyst. Through the BET analysis, it was confirmed that the specific area significantly was increased after ball milling due to the reduced particle size, obtaining the optimized milling time with the higher ORR performance. The electrochemical activities have been measured with rotating disk electrode(RRDE) method. Well-ball milled LSCF catalyst has resulted in the enlargement of specific surface area and increased defective sites, which improve the catalytic activity. To investigate the influence of LSCF oxides on the ORR process, the performance of composite electrode with LSCF catalyst in LITFSI in either solvents has been compared with a carbon based cathode(carbon nano tube(CM130)). From the discharge results, the composite electrode showed the superior performance as well as higher specific capacitance (more than 1.6 times) than carbon based electrode dye to the altered transport and reaction kinetics due to LSCF. In this study, we have proposed the processes of obtaining a catalyst with optimal electrochemical properties through a relatively simple process and applied it to electrode for lithium oxygen batteries.

Gelation of Cathode Electrolytes for Improved Structural Integrity and Enhanced Electrochemical Performance of Li-O2 Batteries

Due to the significantly high theoretical energy density, lithium-oxygen (Li-O2) batteries have been attracting much attention as next generation lithium secondary batteries. Nevertheless, there remain a lot of fundamental challenges to be solved for commercialization of Li-O2 batteries, and the cycling performance of currently reported state-of-the-art Li-O2 batteries is still very poor compared to commercially available Li-ion batteries.[1,2] One of the critical problems for the Li-O2 batteries is the leakage of excess liquid electrolytes from the cathode.[3] During the cell operation, Li2O2 is deposited onto the surface of carbon electrodes, which forces the liquid electrolyte out of the cathode. As a result, the deficiency of liquid electrolytes induces deterioration of the cycling performance. Moreover, the formation of Li2O2 causes serious volume expansion of the carbon cathode, which leads to the structural disintegration of electrodes.[4] To suppress the leakage of electrolytes and disintegration of cathode structures, we are aiming to gelate electrolytes inside the carbon nanotube (CNT) cathodes. Although some gel polymer electrolytes have been reported for Li-O2 batteries so far,[5] gelation of electrolytes inside the cathode has been little investigated. In this study, several types of multi-functional cross-linkers are evaluated to gelate the cathode electrolytes via thermally or UV light-initiated in situ polymerization. By tuning the chemical structure and composition of gelling agents, viscoelastic properties of gels can be broadly controlled. We investigate the effect of gel viscoelasticity and cell restraint pressure on the leakage of electrolyte and mechanical integrity of the CNT cathode, as well as battery performance of the Li-O2 cells. In addition, as another strategy to fabricate CNT-based gel cathodes, solvent-mediated technique is exploited: CNTs, electrolytes, gelling polymers, and volatile solvents are kneaded to form paste films. After evaporation of the solvent, CNT-based gel cathodes were obtained. The relationship between composition and preparation process of the gel cathode and resultant electrochemical performance of Li-O2 cells are studied in detail. We also explore the possibility to reduce the electrolyte amount inside cathodes by gelation toward practically high energy density Li-O2 batteries.

Unraveling the Promotion Effects of a Soluble Cobaltocene Catalyst with Respect to Li-O2 Battery Discharge.

The discharge process of a nonaqueous Li-O2 battery at the cathode is the direct oxygen reduction reaction (ORR) with the formation of discharge product, e.g., Li2O2, deposits on the cathode surface. The aggressive superoxide intermediate generated during the ORR severely degrades the organic electrolyte and carbon-based cathodes. To avoid the formation of superoxide species and promote the growth of Li2O2 in the electrolyte solution, we employ a soluble cobaltocene [Co(C5H5)2, Cp2Co] as a homogeneous molecule catalyst to boost the discharge performance of Li-O2 batteries. Owing to the unique chemical reactivity of Cp2Co with molecular oxygen, the electrochemistry of the discharge process at the cathode is the (Cp2Co)2II-O22- adduct-mediated process rather than direct electrochemical oxygen reduction, thereby avoiding the formation of aggressive superoxide intermediate. In addition, the strong intermolecular attraction between Cp2Co and the newly formed Li2O2 promotes the solution phase growth of Li2O2, which effectively suppresses electrode passivation.

Three-Dimensional Carbon-Supported MoS2 With Sulfur Defects as Oxygen Electrodes for Li-O2 Batteries

Recently, Li-O2 batteries considered to be the promising next-generation energy storage devices owing to their high theoretical specific energy. However due to the sluggish reaction kinetics of oxygen conversion, the practical application can’t achieve the desired results. By introducing vacancies on the MoS2 basal plane and in-situ synthesized method, we demonstrated the excellent catalysis of MoS2-x for oxygen redox kinetics to improve the Li-O2 batteries performance. The prepared MoS2-x displays the small polarization with potential gap of 0.59 V and high discharge capacity of 8851 mA h g-1 at a current density of 500 mA g-1. The improved performances are mainly attributed to abundant S defects and plentiful diffusion channels in the MoS2-x/carbon 3D structural cathodes to adsorb gaseous oxygen, reaction intermediates and discharge products. To the best of knowledge, the fabricated structures have been regarded as one of the excellent oxygen conversion catalysts from 3D network design and surface modulation, offering an open vision for the designing Li-O2 catalysts and beyond.

Perpendicularly aligned TiC-coated carbon cloth cathode for high-performance Li-O2 batteries

To overcome the theoretical energy density limit of current lithium-ion batteries (LIBs), lithium-oxygen (Li-O2) batteries based on electrochemical formation and decomposition of lithium peroxide (Li2O2) have received much attention. However, critical cathode-related issues such as carbon decomposition, irreversible accumulation of Li2O2, and subsequent cathode passivation severely restrict the performance of Li-O2 batteries. To manage these issues, this paper reports a perpendicularly aligned TiC-coated carbon cloth (TiC-cloth) for Li-O2 battery cathodes prepared by a facile carbothermal method using easily available T-shirts as a substrate and growth of TiC on the outer surface. Coating with perpendicularly aligned TiC protects the carbon surface and increases the surface area to accommodate Li2O2. After verification of the successful coating, electrochemical tests of Li-O2 batteries were conducted, and the results were compared against TiC nanoparticle electrode casted manually onto carbonized T-shirts. The TiC-cloth affords enhanced oxygen reduction/evolution activity and cyclability for Li-O2 batteries compared with the TiC nanoparticles. Analyses demonstrate that this improvement arises from the reversible formation and decomposition of Li2O2 grown along the shape of the TiC on the carbonized T-shirts without carbon decomposition. The study reported here will be a keystone for the intelligent design of stable and efficient cathodes for Li-O2 batteries.

Ni3Se2/NiSe2 heterostructure nanoforests as an efficient bifunctional electrocatalyst for high-capacity and long-life Li–O2 batteries

Li–O2 batteries (LOBs) with ultrahigh theoretical energy density are regarded as the most promising next-generation candidates for energy storage and conversion devices. However, the development of LOBs is severely hindered by adverse parasitic reactions and sluggish reaction kinetics. Herein, hierarchical Ni3Se2/NiSe2 heterostructure nanoforests on Ni foam (Ni3Se2/NiSe2@NF) is designed as a high efficient bifunctional electrocatalyst for LOBs. As expected, owing to 3D hierarchically branched nanoforests structure, the Ni3Se2/NiSe2@NF electrode can build up an effective channel for mass transfer and expose sufficient active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In addition, the strong interface interaction between Ni3Se2 and NiSe2 in the heterostructure causes distinct electron redistribution along the interface, which plays a vital role in enhancing electrocatalytic performance of Ni3Se2/NiSe2@NF. Accordingly, LOBs based on Ni3Se2/NiSe2@NF shows a high discharge specific capacity of 23,092 mA h g−1 at 500 mA g−1, a low voltage gap of 0.96 V and an improved cycling life of 500 cycles. It is worth noting that this study has a significant guidance for designing effective bifunctional electrocatalysts via constructing the heterostructure to boost oxygen electrode kinetics and improve Li–O2 battery performance.

A Modeling Study of Discharging Li-O2 Batteries With Various Electrolyte Concentrations

Abstract The mass transfer in the cathode electrode plays an important role in operating Li-O2 batteries. In this study, a two-dimensional, transient, and isothermal model is developed to investigate the mass transfer in discharging Li-O2 batteries. This model simulates the discharge performance of Li-O2 batteries with various electrolyte concentrations (0.1−1.0M) at various current densities (0.1, 0.3, and 0.5 mA/cm2). The O2 diffusivity and the ionic conductivity and diffusivity of Li+ are altered as the bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) concentration in the electrolyte of tetraethylene glycol dimethyl ether (TEGDME) changes. The distributions of O2, Li+, and lithium peroxide (Li2O2) in the cathode electrode after discharge are calculated using this model. Modeling results show that when the concentration decreases from 0.5 to 0.25M, the discharge capacity of Li-O2 sharply drops at various current densities. The mass transfer of Li+ determines the discharge capacity of Li-O2 batteries with dilute electrolytes (≤0.25 M). In contrast, the O2 supply is dominant regarding the discharge capacity when the electrolyte concentration is larger than 0.5M. The highest discharge capacity (e.g., 6.09 mAh at 0.1 mA/cm2) is achieved using 0.5M electrolyte since it balances mass transfer of O2 and Li+.

Study on the Effect of Surface Area on the Oxygen Reduction Reaction Performance of Perovskite Catalyst for Lithium-Oxygen Batteries

Lithium oxygen batteries have been recognized as one of the next-generation power sources, capable of supplying power for a long time even in an independent extreme environment. In spite of the theoretical advantage, Li-O2 batteries face technical and economic challenges that must be addressed to promote them as commercially variable technologies for future energy system. Above all, battery performance largely depends on the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of the cathode during discharge and charge, respectively. The undesirable overpotential caused by sluggish reaction kinetics associated with the ORR and OER greatly limit the current performance of Li-O2 batteries, which must be improved by efficient catalyzing the reactions. Among the numerous catalysts, perovskite oxides have attention for candidate electro catalyst for Li-O2 batteries due to their high electronic/ionic conductivity, high electrochemical stability, and catalytic activity. Especially, La0.6Sr0.4Co0.2Fe0.8O3(LSCF) is considered as a typical catalyst for Li-O2 batteries, which can provide high oxygen surface exchange coefficient for fast kinetics at the gas/electrode interface. The surface area is significantly related on the ORR and OER performance, which influences on the active area for reactions. In this study, we have tried to utilize a simple high energy ball milling process to investigate the electrochemical properties of LSCF catalyst. Through the BET analysis, it was confirmed that the specific area significantly was increased after ball milling due to the reduced particle size, obtaining the optimized milling time with the higher ORR performance. The electrochemical activities have been measured with rotating disk electrode (RRDE) method. Well-ball milled LSCF catalyst has resulted in the enlargement of specific surface area and increased defective sites, which improve the catalytic activity.To investigate the influence of LSCF oxides on the ORR process, the performance of composite electrode with LSCF catalyst in LITFSI in ether solvents has been compared with a carbon based cathode (carbon nano tube(CM130)). From the discharge results, the composite electrode showed the superior performance as well as higher specific capacitance (more than 1.6 times) than carbon based electrode dye to the altered transport and reaction kinetics due to LSCF. In this study, we have proposed the processes of obtaining a catalyst with optimal electrochemical properties through a relatively simple process and applied it to electrode for lithium oxygen batteries.

Realizing the growth of nano-network Li2O2 film on defect-rich holey Co9S8 nanosheets for Li-O2 battery

Confining and controlling the growth of discharge products through favorable nanostructures of the solid catalysts to realize the formation of nanoscale Li2O2 is an effective strategy to reach both high capacity and good reversibility of Li-O2 battery. However, utilizing the nanostructures of the transition metal-based catalysts to realize the deposition of nanoscale Li2O2 is still a challenge. In this work, defect-rich holey 2D Co9S8 nanosheets (H-2D-Co9S8) were firstly synthesized and acted as the cathode catalyst of Li-O2 batteries. The 2D architecture and in-plane holes of the catalyst not only facilitate mass transfer, but also provide the rich sulfur deficiency as active sites. The favorable nanostructure of H-2D-Co9S8 could induce the formation of loose and thick discharge product film constructed by discrete nanoscale Li2O2, which offer a higher capacity (3500 mAh/g based on the total mass of catalyst (70%) and KB (20%)) compared with that of the bulk film-like Li2O2 on the bulk Co9S8. More importantly, the discrete nanoscale Li2O2 could be decomposed more easily because of the improved charge transport and delithiation property derived from its smaller particle size and higher surface area, thus leading to better reversibility of the battery (100 cycles at a limited capacity of 500 mAhg−1). This work provided some new insights into achieving the improvement of the Li-O2 battery performance through confining and controlling the deposition of nanoscale Li2O2 by the favorable nanostructures of the transition metal-based catalysts.

A free-standing CeO2/Co3O4 nanowires electrode featuring a controllable discharge/charge product evolution route with enhanced catalytic performance for Li-O2 batteries

Although transition metal oxides are important potential catalytic cathode materials for Li-O2 batteries (LOBs), their poor cycle durability at high current density, high overpotentials and side reaction are still the challenges to solve. Herein, CeO2/Co3O4 nanowire arrays grown on Ni foam were fabricated as a free standing cathode of LOBs, featuring a controllable discharge/charge products evolution route. CeO2 served as active sites for nucleation, initial growth and decomposition of Li2O2. The embedded CeO2 nanocrystalline on Co3O4 substrate dominated the initial discharge/charge product evolution with multi-formation kinetics of crystal Li2O2 and Li2-xO2 at high current densities which leading to low overpotentials and efficient decomposition of discharge products. Owing to the stable structure, the CeO2/Co3O4 nanowires were found to energetically favor the mass transport between the electrode/electrolyte interface during long cycle testing. As a consequence, excellent cyclability of 500 cycles at high current density (500 mA g−1) under a fixed capacity of 500 mA h g−1 with low overpotentials of 0.2 V and 1.0 V for discharge/charge process (after 500 cycles) were achieved. The present work provides a new strategy and intrinsic insight in designing high-performance metal oxides electrocatalysts with a fine-tuned structure for LOBs.

Stable Lithium Anode of Li–O2 Batteries in a Wet Electrolyte Enabled by a High-Current Treatment

Rechargeable Li-air (O2) batteries have attracted a great deal of attention because of their high theoretical energy density and been regarded as a promising next-generation energy storage technology. Among numerous obstacles to Li-air (O2) batteries preventing their use in practical applications, water is a representative impurity for Li-air (O2), which could hasten the deterioration of the anode and accelarate the premature death of cells. Here, we report an effective in situ high-current pretreatment process to enhance the cycling performance of Li-O2 batteries in a wet tetraethylene glycol dimethyl ether-based electrolyte. With the help of certain levels of H2O (from 100 to 2000 ppm) in the electrolyte, adequate Li2O formed on the lithium anode surface after high-current pretreatment, which is necessary for a robust and uniform solid electrolyte interphase layer to protect Li metal during the long-term discharge-charge cycling process. This in situ high-current pretreatment method in a wet electrolyte is shown to be an effective approach for enhancing the cycling performance of Li-O2 batteries with a stable Li metal anode and promoting the realization of practical Li-air batteries.

Effect of surface bonding of FePC with electrospun carbon nanofiber on electrocatalytic performance for aprotic Li-O2 batteries

The bifunctional catalysts assist the complete reversible cycle of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low polarization of a lithium-oxygen (Li-O2) battery were known to be critical cathode components. In this work, electrospun nitrogen-doped carbon nanofibers (N-CNFs) were prepared to use as supports to anchor iron phthalocyanine (FePc) bifunctional catalyst for oxygen (O2) electrode in Li-O2 batteries. By using FePc and N-CNFs, two different bonding composites were fabricated via diazonium reaction by refluxing and physical mixing methods which were resulting into covalent linkage via pyridine (Py) (denoted as FePc/Py/N-CNFs) and noncovalent interaction via π-π stacking (denoted as FePc/N-CNFs). The systematic characterizations confirmed that the spun carbon nanofibers were functionalized by pyridine and the anchored FePc molecule donated the axial ligand for the iron (Fe) center in the FePc/Py/N-CNFs composite. The FePc were embedded in the N-CNFs composites combining the electrocatalytic activity of the FePc with ORR/OER processes and N-CNFs with a three-dimensional (3D) interconnected porous network structure through a connecting link of one-dimensional (1D) porous and N-doping carbon nanofiber which exhibited a high performance when acting as the cathode in Li-O2 batteries. However, the FePc/Py/N-CNFs composite showed the higher catalytic activity and prominent structural stability due to the FePc being strongly interlinked with the N-CNFs through the Py connection, which could avoid the deformation and agglomeration of FePC molecules during cycling and thus possessed the high electrochemical performance of the composite. This study demonstrated the unique design of FePc/Py/N-CNFs composite structure in this work would be found as a promising O2 electrode material with enhanced electrochemical performance in rechargeable Li-O2 batteries.

Synergic effect of catalyst/binder in passivation side-products of Li-oxygen cells

While used in minor proportion respect to other components in cathode formulations, binders play a crucial role in lithium batteries cathode. This is particularly true in Li-O2 batteries which represent a very harsh environment mainly because of the formation, upon cycling, of very aggressive superoxide radicals. In such batteries, the use of catalyst in the cathode formulation is quite usual to help oxygen reduction reaction and oxygen evolution reaction (ORR and OER) to proceed rapidly and reversibly. However, the slightest binder degradation upon cycling can hinder the catalyst effects dramatically, modifying them to act on other reactions associated with the generated side-products, thus deteriorating cell performances and preventing researchers from drawing the right conclusions about catalytic properties of new materials. In this work, the influence of different catalysts in the degradation of the PVDF binder, on the performance of Li-O2 batteries, was investigated. The results obtained were compared with the ones of cathodes prepared with the same catalysts but Li-Nafion binder instead (already reported as stable), to further demonstrate that the choice of binder must be strongly linked to the nature of the catalyst. The catalysts employed for this study were α-MnO2, and commercial Co3O4, and Co phthalocyanines (CoPc).

Preparation of pyridine N-doped metal-free Li–O2 battery cathode by one-step

Lithium-oxygen (Li–O2) batteries are an ideal energy storage device, but the problems of the cathode still hinder their development. In this work, a metal-free, binder-free and in situ pyridine N-doped cathode of Li–O2 batteries is synthesized in one step by electrospinning. Meanwhile, the effect of carbonization temperature on cathode is discussed in detail. The content of pyridine N in the cathode is the highest at the carbonization temperature of 700 °C, and it is also the most effective for the reversible formation and decomposition of Li2O2. In terms of Li–O2 batteries performance, when the charge and discharge current density is 100 mA g−1 and the discharge voltage is greater than 2 V, the discharge specific capacity and discharge capacity can reach 27900 mAh g−1 and 27.9 mAh respectively. In addition, when the limited specific capacity is 1000 mAh g−1, the batteries can work stably for 85 cycles under the same conditions. Therefore, the high-performance cathode which synthesized in one step by electrospinning is expected to promote the commercial application of Li–O2 batteries.

Radially ordered carbon nanotubes performance for Li-O2 batteries: Pre-treatment influence on capacity and discharge products

Abstract We report a novel electrode for Li-O2 battery based on radially ordered multi-walled carbon nanotubes functionalized by acid and plasma pre-treatments without degrading its structure with improved wettability leading to more effective active sites. This electrode was used in a device with DMSO/LiClO4 as the electrolyte, presenting good discharge capacity result (2804 mA h g−1C). The defects on the nanotube structure were characterized with RAMAN and a correlation from defects and discharge capacity was observed indicating that the defects could provide larger number of effective regions for discharge products. Raman, FTIR and synchrotron X-ray diffraction characterization over the discharged electrode revealed a large formation of Li2CO3 as the main product, which is uncommon for this system. Further characterization of composition and morphology in time-elapsed discharge also supported a continuous carbonate formation. By limiting the discharge capacity to 500 mA h.g−1C, an improvement in the cycling was observed, however, the higher overpotential needed to decompose the discharge product limited the cell performance.