Morphology Of Discharge Products Research Articles

The effect of water admixture on aprotic Mg-O2 battery performance

Generally, aprotic Li-O2 batteries performance is significantly influenced by water impurity in electrolyte/gas via promotion of Li2O2 mesocrystallization. In the case of promising alkali-earth metals this issue remains unexplored. Here we have studied the role of water content in DMSO-based electrolyte in discharge process of Mg-O2 cells with metallic magnesium anode and carbon cathode. We found that water impurity in the electrolyte is not a key factor determining the discharge capacity for a Mg-O2 battery, at least in a single-compartment cell. Morphology of discharge product does not change upon addition 8000 ppm of water. Discharge products contain major amount of electrolyte byproducts and negligible concentration of magnesium peroxide. Under high water content (more than 8000 ppm) Mg(OH)2 is also formed as discharge product, but content of by-products still remains high.

Engineering the Electronic Interaction between Atomically Dispersed Fe and RuO2 Attaining High Catalytic Activity and Durability Catalyst for Li-O2 Battery.

It is significant to develop catalysts with high catalytic activity and durability to improve the electrochemical performances of lithium-oxygen batteries (LOBs). While electronic metal-support interaction (EMSI) between metal atoms and support has shown great potential in catalytic field. Hence, to effectively improve the electrochemical performance of LOBs, atomically dispersed Fe modified RuO2 nanoparticles are designed to be loaded on hierarchical porous carbon shells (FeSA -RuO2 /HPCS) based on EMSI criterion. It is revealed that the Ru-O-Fe1 structure is formed between the atomically dispersed Fe atoms and the surrounding Ru sites through electron interaction, and this structure could act as the ultra-high activity driving force center of oxygen reduction/evolution reaction (ORR/OER). Specifically, the Ru-O-Fe1 structure enhances the reaction kinetics of ORR to a certain extent, and optimizes the morphology of discharge products by reducing the adsorption energy of catalyst for O2 and LiO2 ; while during the OER process, the Ru-O-Fe1 structure not only greatly enhances the reaction kinetics of OER, but also catalyzes the efficient decomposition of the discharge products Li2 O2 by the favorable electron transfer between the active sites and the discharge products. Hence, LOBs based on FeSA-RuO2 /HPCS cathodes show an ultra-low over-potential, high discharge capacity and superior durability.

Tailoring the nucleation and growth routes of discharge products for lithium-oxygen batteries through the facet engineering of Ni2P catalysts

Li-O2 batteries (LOBs) with high theoretic energy densities are regarded as potential energy storage devices. However, the insulative discharge product, Li2O2, would accumulate on the cathode, restricting the depth of discharge and raising barriers for charge. The rational catalyst design is proposed as an efficient strategy to tailor growth routes and morphology of Li2O2, and consequently address the above issue. Herein, porous Ni2P nanorods with exposed (0001) or (101¯0) facets are prepared on Ni foams through the heat treatment of Ni2P2O7 arrays in a PH3 atmosphere. The exposed facets of Ni2P nanorods could be well controlled through the variation of the hydrothermal reaction time for Ni2P2O7. Employed as free-standing cathodes for LOBs, Ni2P nanorods with exposed (0001) facets exhibit superior electrochemical performance than those nanorods with exposed (101¯0) facets due to the interaction between exposed facets and the nucleation, growth of LiO2 or Li2O2, consequently tuning the morphology of discharge products. The high electron transfer rate and weak adsorption energy of LiO2 on exposed (0001) facets could promote the generation rate of the (solvated) LiO2, inducing the formation of large Li2O2 sheets (over 30 μm) and further growth of flower-like nanoflake assemblies (∼500 nm) on the surface of Li2O2 sheets assignable to the variation of the surface environment of the cathode during the discharge process, exhibiting more Li2O2 deposited at full coverage of cathode surface. It is proposed that the facet engineering is a feasible way to improve the electrochemical performance of cathode catalysts for LOBs.

Interface engineering of Co3O4/CeO2 heterostructure in-situ embedded in Co/N‑doped carbon nanofibers integrating oxygen vacancies as effective oxygen cathode catalyst for Li-O2 battery

The construction of heterostructure and rational regulation of electronic band structure toward electrocatalyst is crucial to essentially reform the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities in Li-O2 batteries. Herein, a simple electrospinning strategy combining subsequent annealing process for the construction of Co3O4/CeO2p-n heterojunction in-situ embedded in Co/N-doped carbon nanofiber (Co3O4/CeO2@Co/N-CNF) derived from metal-organic framework (MOF) is developed. The coupled heterogeneous interface and highly concentrated oxygen vacancies ensure a rapid charge transfer between Co3O4 and CeO2, leading to and changed electronic state and rich defect sites. Accordingly, the prepared Co3O4/CeO2@Co/N-CNF catalyzed Li-O2 battery delivers a low voltage gap (0.87 V at a middle capacity of 500 mAh/g), high discharge/charge specific capacities (9667.3/9317.3 mAh/g at 100 mA g−1), and improved cycling lifespan (exceed 70 cycles at 100 mA g−1). In addition, interface engineering of heterostructure electrocatalysts can effectively regulate the morphology of discharge products. This research offers a new insight into the construction of heterojunction to boost the electrocatalytic performance of Li-O2 batteries.

Compressible, gradient-immersion, regenerable carbon nanotube sponges as high-performance lithium–oxygen battery cathodes

Lithium–oxygen batteries promise ultrahigh energy density, yet one of the key barriers toward applications is the rapid performance decay during cycling especially at high rates, owing to the sluggish redox kinetics and severe parasitic reactions under elevated overpotentials within the cathode. In face of the above challenge, here we present a carbon nanotube sponge-based high-performance lithium–oxygen cathode by a series of approaches such as tailoring discharge product morphology to lower the overpotential, controlled sponge-compression for high mass loading to facilitate high-rate cycling, gradient electrolyte-immersion to rationally utilize its interior for efficient multiphase transport, and water treating for regenerated use. These 4 methods target different aspects of the electrochemical behavior in a Li–O2 cathode, thus constituting a complementary and integrated strategy to overcome the challenges in this field. As a result, we achieve simultaneously an ultralong cycle life (1423 cycles, 2846 h) at high rate (0.5 mA cm−2) under low overpotential (charging below 4.0 V throughout 1100 cycles), also with an areal capacity over 20 mAh cm−2 and extended 500 cycles after regeneration. Such an overall performance is much superior to recently developed 3D metal foam or carbon-based cathodes. Our designed sponge cathode represents a promising candidate for developing durable, high-energy and high-power metal–air battery systems, pushing forward their practical application.

Crystal Phase Conversion on Cobalt Oxide: Stable Adsorption toward LiO2 for Film-Like Discharge Products Generation in Li-O2 Battery.

Regulating the structure and morphology of discharge product is one of the key points for developing high performance Li-O2 batteries (LOBs). In this study, the reaction mechanism of LOB is successfully controlled by the regulated fine structure of cobalt oxide through tuning the crystallization process. It is demonstrated that the cobalt oxide with lower crystallinity shows stronger affinity toward LiO2 , inducing the growth of film-like LiO2 on the electrode surface and inhibiting the further conversion to Li2 O2 . The batteries catalyzed by the lower crystallinity cobalt oxide hollow spheres which pyrolyzed from ZIF-67 at 260°C (ZIF-67-260), go through the generation and decomposition of amorphous film-like LiO2 , which significantly reduces the charge overpotential and improves the cycle life. By contrast, the ZIF-67 hollow spheres pyrolyzed at 320°C (ZIF-67-320) with better crystallinity are more likely to go through the solution-mediated mechanism and induce the aggregation of discharge product, resulting in the sluggish kinetics and limited performance. The combined density functional theory data also directly support the strong relationship between the adsorption toward LiO2 by the electrocatalyst and the battery performance. This work provides an important way for tuning the intermediate and constructing the high-performance battery system.

Interrogation of the Reaction Mechanism in a Na-O2 Battery Using In Situ Transmission Electron Microscopy.

Critical factors that govern the composition and morphology of discharge products are largely unknown for Na-O2 batteries. Here we report a reversible oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process in a sodium-oxygen battery observed using in situ environmental-transmission electron microscopy (TEM) experiment. The reaction mechanism and phase evolution are probed using in situ electron diffraction and TEM imaging. The reversible ORR and OER cycling lies upon the nanosized copper clusters that were formed in situ by sodiation of CuS. In situ electron diffraction revealed the formation of NaO2 initially, which then disproportionated into orthorhombic and hexagonal Na2O2 and O2. Na2O2 was the major final ORR product that uniformly covered the whole wire-shape cathode. This uniform product morphology largely increased the application feasibility of Na-O2 batteries in industry. In the following OER process, the Na2O2 transformed to NaO2, which resulted in volume expansion at first, and then the NaO2 decomposed to sodium ions and O2 gas. Galvanostatic charge/discharge profiles of CuS in real Na-O2 cells revealed a maximum capacity over 3 mAh cm-2 with a discharge cutoff voltage of 1.8 V and high cycling stability. The nanosized copper catalyst plays a dominating role in controlling the morphology, chemical composition of discharge products, and reversibility of this Na-O2 battery. Our finding shines light on the exploration of effective catalysts for the Na-O2 battery.

Aprotic Li/O2 Batteries: Reactions and Products in Electrolytes with and without a Redox Mediator

The interest in secondary Li/O2 batteries has grown rapidly over the past two decades, as they exhibit a practically achieveable specific energy of about 1,700 Wh/kg, which equals that of gasoline and is well beyond those of conventional lithium ion, Ni metal hydride and Zn/air batteries.1,2 The large energy density is due to the very light-weight cell components: a Li metal anode, a porous C cathode (gas diffusion electrode, GDE) and gaseous O2 as active cathode material. During discharge LiO2 and Li2O2 (as well as Li2O) are formed via the oxygen reduction reaction (ORR) in the porous carbon matrix. These products are oxidized again upon recharge. This seemingly simple system, however, has some major drawbacks due to the decomposition of the organic electrolytes during battery cycling – which is caused by the reaction of the respective electrolyte with either the Li anode, different components of the GDE and/or even the desired ORR products. The decomposition products are deposited in the GDE pores, leading to a minimized active electrode surface, decreasing capacities and ultimately cell failure upon continued cycling.3 There are two major reaction mechanisms leading to the formation if Li2O2, and the prevailing mechanism depends on the electrolyte. Li2O2 toroids are a common discharge product of the so-called solution growth pathway proceeding via an EC mechanism4: O2 is reduced to O2 -, which is dissolved and forms LiO2. The solvated LiO2 intermediates subsequently disproportionate to solid Li2O2 particles with different morphologies (which depend on the nature of the electrolyte)5. The ORR proceeds primarily via this mechanism when high DN electrolyte solvents are used and/or discharge parameters, such as low discharge current densities and low overpotentials, are applied6. With low DN solvents and/or high current densities and overpotentials, the discharge reaction proceeds via the surface growth pathway. In this work, galvanostatic cycling and CV measurements were conducted with 1 M mixtures of LiTFSI/DMSO and LiTFSI/TEGDME, with and without additions of the redox mediator dimethylphenazine, DMPZ7, to analyze the electrolyte influence on the cycling behavior. At different states of charge, the GDE surface and pores were investigated by SEM and XRD to obtain information on the nature, the morphology and the distribution of the product deposits on and in the carbon structure. Galvanostatic cycling measurements show a larger discharge capacity and lower discharge overpotential with LiTFSI/DMSO as well as a better recharge behavior in the first cycle, although both electrolytes exhibit very high recharge potentials. The TEGDME-based electrolyte on the other hand exhibits a higher stability over the first five cycles, whereas the discharge capacity of LiTFSI/DMSO decreases drastically already upon second discharge. CV measurements confirm these absolute and relative trends of the discharge capacities. A SEM investigation of the GDE surfaces after first discharge reveals a considerable difference in discharge product morphology depending on the electrolyte. This is in agreement to previously published results: with DMSO as solvent the product consists of toroidal particles with diameters of approximately 200 nm, whereas discharge with the TEGDME-based electrolyte yields a product layer on the porous cathode surface.5,8 Differential capacity analysis confirmed the difference in discharge product formation: with LiTFSI/TEGDME two reduction processes were detected to contribute to the discharge capacity, whereas discharge with LiTFSI/DMSO contains only one reduction process. X-ray diffraction after the first discharge with LiTFSI/DMSO shows the presence of crystalline Li2O2 in the GDE and the absence of crystalline LiOH. The discharge with the TEGDME-based electrolyte, on the other hand, did not yield any crystalline Li2O2 (or LiOH). FIB-SEM measurements after the first discharge with each electrolyte furthermore showed that the GDE pores were almost completely blocked by bulk product. The addition of the DMPZ significantly reduced the charging potential, both for the DMSO and the TEGDME electrolyte. The cycling performance was, however, only improved for DMSO, and not for TEGDME. Bruce et al., Nat. Mater. (2012) 11, 19-29.Yao et al., Angew. Chem. Int. Ed. (2016) 55, 11344-11353.Sharon et al., Isr. J. Chem. (2015) 55, 508-520.Johnson, L. et al., Nat. Chem. 6, 1091–1099 (2014).Mitchell, R. R., et al., J. Phys. Chem. Lett. 4, 1060–1064 (2013).Aurbach, D., et al., Nat. Energy 1, 16128 (2016).Lim et al., Nature Energy (2016) 1, 16066.Aetukuri et al., Nat. Chem. (2014) 7, 50-56.

Inside the electrode: Looking at cycling products in Li/O2 batteries

This work investigates the impact of electrochemical reactions and products on discharge capacity and cycling stability with electrolytes based on two common solvents – tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO).Although the DMSO-based electrolyte exhibits better initial electrochemical properties compared to that based on TEGDME, e.g., higher discharge capacity and potential, the use of TEGDME results in a significantly better cycling stability.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations of the gas diffusion electrodes (GDE) after first discharge reveal a considerable difference in discharge product morphology. With DMSO as solvent one high-potential reduction process leads to the formation of crystalline lithium peroxide (Li2O2) particles on the cathode surface area. SEM imaging of GDE cross-sections depicts that the (non-crystalline) product film formation at lower potentials during discharge with the TEGDME-based electrolyte results in a GDE pore clogging close to the O2 inlet, so that gas transport is hindered and the discharge ends at an earlier point. The higher cycling stability with LiTFSI/TEGDME, however, is attributed to (i) the apparently complete recovery of the GDE active surface by recharge and (ii) different parasitic reactions resulting in the formation of side product particles rather than films.

Metal–organic framework derived Co–N-reduced graphene oxide as electrode materials for rechargeable Li–O2 batteries

With tailored deposition sites and morphology of discharge products, the Li–O2 batteries based on Co–N-rGO electrodes exhibit significant enhancement.

Aprotic Li/O2 Batteries: Reactions and Products in Different Electrolytes

The interest in secondary Li/O2 batteries has grown rapidly over the past two decades, as they exhibit a practically achieveable specific energy of about 1,700 Wh/kg, which equals that of gasoline and is well beyond those of conventional lithium ion, Ni metal hydride and Zn/air batteries.1,2 The large energy density is due to the very light-weight cell components: a Li metal anode, a porous C cathode (gas diffusion electrode, GDE) and gaseous O2 as active cathode material. During discharge LiO2 and Li2O2 (as well as Li2O) are formed via the oxygen reduction reaction (ORR) in the porous carbon matrix. These products are re-oxidized upon recharge. The major drawback of this seemingly simple system, however, is the reactivity of the organic electrolytes with almost all battery components and hence several decomposition reactions. The resulting side products are deposited in the GDE pores, leading to a minimized active electrode surface and ultimately cell failure upon continued cycling.3 Therefore, information on the electrolyte-dependent ORR and/or decomposition products deposited in the GDE during discharge is needed for an in-depth investigation of the causes for early battery failure. In order to achieve this, galvanostatic cycling and CV measurements were conducted with 1 M mixtures of LiTFSI/DMSO and LiTFSI/TEGDME to analyze the electrolyte influence on the cycling behavior. At different states of charge, the GDE surface and pores were investigated by SEM and XRD to obtain information about the product deposits on and in the carbon structure. Galvanostatic cycling measurements show a larger discharge capacity and lower discharge overpotential with LiTFSI/DMSO as well as a better recharge behavior in the first cycle (see Fig. 1.a). The TEGDME-based electrolyte on the other hand exhibits a higher long-term stability, whereas the discharge capacity of LiTFSI/DMSO decreases drastically already upon the second discharge (see Fig. 1.b). CV measurements confirm these absolute and relative trends of the discharge capacities (see inset in Fig. 1.b). A SEM investigation of the GDE surfaces after first discharge reveals a considerable difference in discharge product morphology depending on the electrolyte. This is in agreement to previously published reports:4,5 with DMSO as solvent the product consists of toroidal particles with diameters of approximately 200 nm (see Fig. 1.c), whereas discharge with the TEGDME-based electrolyte yields a product layer on the porous cathode surface (see Fig. 1d). Differential capacity analysis confirmed the difference in discharge product formation: with LiTFSI/TEGDME two reduction processes were detected to contribute to the discharge capacity, whereas discharge with LiTFSI/DMSO contains only one reduction process. X-ray diffraction after the first discharge with LiTFSI/DMSO shows the presence of crystalline Li2O2 as well as a minor amount of LiOH in the GDE (see Fig. 1.e). The discharge with the TEGDME-based electrolyte, on the other hand, did not yield crystalline Li2O2 but only a small amount of LiOH. FIB-SEM measurements after the first discharge with each electrolytes furthermore showed that the GDE pores were almost completely blocked by bulk product. Despite the absence of crystalline Li2O2 a comparison of SEM images after recharge with both electrolytes revealed a better cathode surface as well as pore recovery when using LiTFSI/TEGDME. This fact is most probably the reason for the significantly higher cycling stability with this electrolyte. In order to obtain a more complete picture on the obtained results, the replacement of LiTFSI by other Li+ ion conducting salts, e.g., LiClO4 and LiNO3, as well as the use of electrolyte additives, such as the promising tetrathiafulvalene and dimethylphenazine,6 will be investigated and compared to LiTFSI/DMSO and LiTFSI/TEGDME. Acknowledgments The Research Council of Norway is acknowledged for the financial support within the framework of the research project "Optimized electrode-electrolyte interfaces for Li-air batteries" (contract number 240 866). The Research Council of Norway is also acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab, project number 245963/F50. References Bruce et al., Mater. (2012) 11, 19-29.Yao et al., Chem. Int. Ed. (2016) 55, 11344-11353.Sharon et al., J. Chem. (2015) 55, 508-520.Aetukuri et al., Chem. (2014) 7, 50-56.Mitchell et al., Phys. Chem. Lett. (2013) 4, 1060-1064.Lim et al., Nature Energy (2016) 1, 16066. Figure 1

Elucidating the Impact of Sodium Salt Concentration on the Cathode–Electrolyte Interface of Na–Air Batteries

A promising approach to improve the specific capacity and cyclability in a Na–O2 cell using a pyrrolidinium-based ionic liquid electrolyte in a half-cell has been explored in this work. Increasing the concentration of sodium salt in an ionic liquid electrolyte produces a significant enhancement in the discharge capacity of up to 10 times, a reduction in the overpotential and an increase in the long-term cyclability. Additionally, a distinct discharge morphology is also observed, which is demonstrated to be result of a different oxygen reduction reaction mechanisms. These improvements are likely due to the solvation of Na+ in the electrolyte mixtures containing different Na+ concentrations; the coordination of Na+ by the anion of the ionic liquid dictates the discharge product morphology. At low concentrations, Na+ is strongly coordinated to the anion of the ionic liquid, and this also can have an effect on its mobility; however, at high Na+ concentration, this interaction is weakened and favors mass trans...

High-Performance Na-O2 Batteries Enabled by Oriented NaO2 Nanowires as Discharge Products.

Na-O2 batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO2 nanowires inside Na-O2 batteries that significantly boosts the performance of Na-O2 batteries. For this purpose, a high-spin Co3O4 electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO2 nanowires are 10-20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na-O2 batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g-1, an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na-O2 batteries but also opens up the opportunity to explore growing nanowires in novel conditions.

Hierarchical Porous Carbon Spheres As an Effective Air Electrode for Li-O2 Batteries

For years, lithium oxygen (Li-O2) battery has been attracted attention thanks to extremely high energy density which might substitute natural resource [1-3]. However, several issues have obstructed the practical application of Li–O2 batteries such as poor rate capability, low energy efficiency and short cycle life [4-6]. To overcome those drawbacks, herein we propose a novel approach for preparing multi porous hierarchal (micro-, meso-, and macro-) carbon as an efficient positive electrode for Li-O2 batteries. Unlike currently existing carbon material, the hierarchical porous carbon spheres have the integrity to accelerate O2 gas flowing and electrolyte circulation (Li+ and O2-), and to provide enough space for Li2O2 accumulation and O2/Li2O2 transformation. As-synthesized cathode delivered higher discharge capacity (3891 mAh g-1 c) than that of Super P cathode (2427 mAh g-1 c) in deep charge/discharge condition and guided to a high round trip efficiency (~70%) compared to that of carbon black (Super P) (~63%), and efficiently boosted the overall electrochemical performance of the Li–O2 batteries. Furthermore, ruthenium (Ru) nanoparticles were uniformly dispersed inside the hierarchical architecture to increase the cathode surface adsorption energy toward O2 and decrease the over potential further, thus get benefit from the greater energy efficiency. Ru inclusion in our multi porous hierarchal carbon electrode (Triple hierarchical porous carbon spheres, THPC) effectively modified the morphology of discharge product (Li2O2) to a uniform toroidal-shaped, which is renowned for advancing the OER performance. Certainly, appreciation goes to the unique multi-porous structure of THPC cathode which offered a large number of active sites and allowed a uniform distribution Ru catalyst, thus facilitated a high capacity with prolonged cycle life alongside high energy efficiency.

Preparation of Polymer-Derived Nitrogen-Doped Hollow Carbon Nanofiber As a Free Standing Oxygen Electrode for Li-O2 Battery

Li-O2 battery has got much attention as a beyond Li-ion battery (LIB), due to its higher energy density and exceeding specific capacity than those of commercial LIB. Though it has a promising potential for large-scale energy storage device, Li-O2 battery still has several problems to be overcome in aspects of poor rate capability and limited stability. Especially, the oxygen electrode is one of the most closely related component to the performance of Li-O2 battery since it is the actual site for formation and decomposition of discharge products. Thus, in order to achieve the Li-O2 battery with improved performance, the oxygen electrode should provide favorable structure for not only discharge product storage, but also facile transfer of reactants such as Li ion and O2. Moreover, bicatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is also significant on oxygen electrode by determining the morphology of discharge product. Furthermore, the oxygen electrode has to be chemically and electrochemically stable as well for extended durability of Li-O2 battery. In this regards, we develop a binder free oxygen electrode composed of nitrogen-doped hollow carbon nanofiber, which is derived from nitrogen-containing polymer. Each carbon nanofiber has an empty space inside the fiber even after the heat treatment at high temperature of 900 °C, and it can facilitate the mass transfer of reactants. Due to this unique structure and high nitrogen content of 4.5 at. %, nitrogen-doped hollow carbon nanofiber indicates the lower ORR overpotential and larger discharge capacity than commercial carbon material, Super P, as shown in Fig. 1. Interestingly, it shows the reduced ORR/OER overpotential which is lower than 1 V with the curtaining capacity of 500 mAh g-1 carbon. The notably reduced overpotential might be attributable to the synergetic effect of nitrogen doping, unique structure of hollow carbon nanofiber and absence of binder by promoting the catalytic activity, facilitating the mass transfer and suppressing the side reactions, respectively. The effects of heat treatment temperature and metal incorporation are also investigated and optimized. As for the result, it can be demonstrated that the binder-free nitrogen-doped hollow carbon nanofiber is an enhanced oxygen electrode of Li-O2 battery. Figure 1

Fe2O3 Nanoparticle Seed Catalysts Enhance Cyclability on Deep (Dis)charge in Aprotic LiO2 Batteries

AbstractAlthough the high energy density of LiO2 chemistry is promising for vehicle electrification, the poor stability and parasitic reactions associated with carbon‐based cathodes and the insulating nature of discharge products limit their rechargeability and energy density. In this study, a cathode material consisting of α‐Fe2O3 nanoseeds and carbon nanotubes (CNT) is presented, which achieves excellent cycling stability on deep (dis)charge with high capacity. The initial capacity of Fe2O3/CNT electrode reaches 805 mA h g−1 (0.7 mA h cm−2) at 0.2 mA cm−2, while maintaining a capacity of 1098 mA h g−1 (0.95 mA h cm−2) after 50 cycles. The operando structural, spectroscopic, and morphological analysis on the evolution of Li2O2 indicates preferential Li2O2 growth on the Fe2O3. The similar d‐spacing of the (100) Li2O2 and (104) Fe2O3 planes suggest that the latter epitaxially induces Li2O2 nucleation. This results in larger Li2O2 primary crystallites and smaller secondary particles compared to that deposited on CNT, which enhances the reversibility of the Li2O2 formation and leads to more stable interfaces within the electrode. The mechanistic insights into dual‐functional materials that act both as stable host substrates and promote redox reactions in LiO2 batteries represent new opportunities for optimizing the discharge product morphology, leading to high cycling stability and coulombic efficiency.

Tailoring the components and morphology of discharge products towards highly rechargeable Li–CO/CO2 batteries

A new non-aqueous Li-CO/CO2 battery with the main discharge products being Li2CO3 and carbon is introduced for the first time. Our findings demonstrate that with the addition of CO, the components and morphology of the discharge products are skillfully tailored, becoming more uniform, with poorer crystallinity and better conductivity. Thanks to these features, the utilization of a cathode in the Li-CO/CO2 battery system is increased and the discharge products are more easily decomposed. These positive effects caused by CO endow the Li-CO/CO2 battery with enhanced electrochemical performances.

CeO2@NiCo2O4 nanowire arrays on carbon textiles as high performance cathode for Li-O2 batteries

The successful development of Li-O2 battery technology depends on developing a stable and efficient cathode. As an important step toward this goal, for the first time, we report the development of CeO2 nanoparticles modified NiCo2O4 nanowire arrays (NWAs) grown on the carbon textiles as a new carbon-free and binder-free cathode system. In this study, the Li-O2 battery with the CeO2@NiCo2O4 NWAs has exhibited much reduced overpotentials, a high discharge capacity, an improved cycling stability, outperforming the Li-O2 battery with NiCo2O4 NWAs. These improvements can be attributed to both the tailored morphology of discharge product and improved oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity after CeO2 NPs deposition. To a considerable extent, this idea of cathode construction including structure design and composition optimization can provide guidance for further researches in developing more powerful cathode for Li-O2 battery.

Improving Electrochemical Performances of Rechargeable Li−CO2 Batteries with an Electrolyte Redox Mediator

AbstractRechargeable Li−CO2 batteries represent a novel approach towards clean recycling and utilization of CO2. Nevertheless, there are still many obstacles to be overcome. Herein, we report the first application of an electrolyte redox mediator (LiBr) in rechargeable Li−CO2 batteries. The electrochemical performances were found to be significantly improved, especially in terms of cyclic stability and rate capability. The proposed mechanism is that LiBr is beneficial for the formation of the desired morphology of discharge products. Moreover, the electrochemically generated Br2 promotes the decomposition of Li2CO3 chemically during the charging process.

Computational Design and Sensitivity Analysis of Non-Aqueous Lithium O2 Batteries

In this study, a gradient-based optimization algorithm is used for the computational design and optimization of a non-aqueous lithium-O2 battery. The sensitivity analysis and numerical optimization capabilities are appended to the multiscale framework previously developed at LRCS for the discharge behavior of this type of batteries. The transport of oxygen in the porous cathode is modeled using Fick’s law at the continuum scale, by assuming isothermal conditions. A micro-scale model predicting the discharge product morphology is coupled to the continuum one. The final discharge product is assumed to form, through both the surface limited thin film growth mechanism and the solution phase reaction mechanism. The cathode microstructure in the model is based on experimentally measured PSD (pore size distribution). A detailed reaction mechanism considering the microstructural properties of the cathode, the surface limited reaction, surface thin film growth and solution phase reaction is used. The sensitivity analysis for the Lithium-O2 cell is performed using the finite difference approach. Sensitivity derivatives are used to identify the variables that have the most significant impact on design performance of the battery. This information is helpful prior to an optimization study as it can be used to remove design parameters that do not strongly influence. Design variables investigated are the O2diffusion coefficient, the cathode porosity, temperature, separator porosity and the cathode thickness. The cell performance is optimized and improved using a quasi-Newton algorithm. In the quasi-Newton algorithm, sensitivity derivatives are utilized in determining a search direction that maximizes a cost function representing the cell capacity. This work provides a comprehensive receipt on the implementation of efficient algorithms devoted to the predictions of optimized cell designs. Design guidelines arising from the computational results are discussed from an engineering perspective.