Non-aqueous Lithium-oxygen Batteries Research Articles

Hierarchically Interconnected 3D Catalyst Structure of Porous Multi-Metal Oxide Nanofibers for High-Performance Li-O2 Batteries.

Non-aqueous lithium-oxygen batteries (LOBs) have emerged as a promising candidate due to their high theoretical energy density and eco-friendly cathode reaction materials. However, LOBs still suffer from high overpotential and poor cycling stability resulting from difficulties in the decomposition of discharge reaction Li2 O2 products. Here, a 3D open network catalyst structure is proposed based on highly-thin and porous multi-metal oxide nanofibers (MMONFs) developed by a facile electrospinning approach coupled with a heat treatment process. The developed hierarchically interconnected 3D porous MMONFs catalyst structure with high specific surface area and porosity shows the enhanced electrochemical reaction kinetics associated with Li2 O2 formation and decomposition on the cathode surface during the charge and discharge processes. The uniquely assembled cathode materials with MMONFs exhibit excellent electrochemical performance with energy efficiency of 82% at a current density of 50mAg-1 and a long-term cycling stability over 100 cycles at 200mAg-1 with a cut-off capacity of 500 mAhg-1 . Moreover, the optimized cathode materials exhibit a remarkable energy density of 1013Whkg-1 at the 100th discharge and charge cycle, which is nearly four times higher than that of C/NMC721, which has the highest energy density among the cathode materials currently used in electric vehicles.

Electrochemical Analysis of Charge Overpotentials in Non-Aqueous Lithium and Sodium Oxygen Batteries

Aprotic metal-oxygen batteries, especially Li-O2 and Na-O2 batteries, could afford theoretical specific energies of more than 500 Wh/kg. However, while not compromising on rechargeability, the practical realization of the theoretically possible high specific energies has been elusive. A better understanding of the differences and similarities between Li–O2 and Na–O2 battery systems in terms of charge-discharge mechanisms and parasitic chemistry will be meaningful in solving these challenges. Here, we explore the differences between the two systems using a combination of galvanostatic charge-discharge measurements, Differential Electrochemical Mass spectrometry (DEMS), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) analysis. The discharge profiles of these battery chemistries are similar in terms of overpotential and have been widely studied. But the origins of the differences in charge overpotentials are not clear. Using in-situ pressure decay measurements during discharge, we calculated the number of electrons/oxygen (e-/O2) to be 2.02 and 1.01 for Li-O2 and Na-O2 cells, respectively. Further, DEMS analysis during charge has shown that the ideal 2 e-/O2 is attained only during the initial phases of charging for Li-O2 cells. However, for Na-O2, the ideal 1 e-/O2 is achieved during a signification portion of the galvanostatic charge step. We corroborate these findings with PEIS and distribution of relaxation times (DRT) analysis to develop a mechanistic view of the processes that lead to poor coulombic and oxygen evolution efficiencies in metal-oxygen cells. Based on DRT analysis, we identify a lower time constant process that is common to both Li-O2 and Na-O2 cells. Interestingly, we observed that voltage polarization is preceded by the observation of this lower time constant peak. In the case of Li-O2 cells, this lower time constant process was observed at the end of discharge and throughout the recharge process, while for the Na-O2 cells, this was only observed after about 70% of recharge. We discuss the possible origins of this low time-constant process and its implications for recharging metal-oxygen batteries. We will also discuss the role of singlet oxygen, if any, in the recharge efficiencies of these two aprotic metal-oxygen batteries. Our results imply that the identification of the origins of this lower time constant process and possible suppression of this process will be key for rechargeable metal-oxygen batteries.

Understanding interaction mechanism between δ-MnO2 and Li2O2 in nonaqueous lithium-oxygen batteries

Focusing on the δ-MnO2 acting as catalysts in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes of the cathode in nonaqueous lithium-oxygen battery, the adsorption models of key intermediates LixOy on the δ-MnO2 surface and the interface model of δ-MnO2 and Li2O2 crystals are established based on density functional theory (DFT) calculations. In terms to the energy change, the δ-MnO2 shows appropriate adsorption energy to the Li2O2 molecule and crystal, benefiting to the proceeding of ORR and OER processes. As for the electron distribution, the δ-MnO2 is an indirect band gap semi-conductor, the semi-conductive characteristic is preserved after the LixOy adsorption, going against the initial Li2O2 nucleation. During the OER process, the three-phase interface of δ-MnO2/Li2O2/O2 proves to be electronic conductive, guaranteeing the capability of combination between electrons and lithium ions. To further optimize the electronic conductivity of δ-MnO2, the δ-MnO2 doped with Li element, which proves to be a stable structure, is proposed to enhance the catalytic activity.

Effects of cathode structure on the discharge performance of non-aqueous Li-O2 batteries

The models of non-aqueous lithium-oxygen (Li-O2) batteries with the flooded electrode (FE) and partially wetted electrode (PWE) are established based on TEGDME electrolyte, considering the movement of electrolyte interface caused by the evolution of solid-phase. The models are verified by comparing the discharge curves at different electrolyte contents. Then the influence of electrolyte filling modes, non-uniform porosity distributions and ultra-thin electrode (UTE) on the discharge performance is explored. As demonstrated by the results, PWE exhibits superior discharge capacity and rate performance due to the reduction of O2 transport distance in the electrolyte, and the specific capacity of PWE is 2305 mAh g−1 at 0.5 mA cm−2, about 10.8 times that of FE. And PWE is not sensitive to the evolution of electrode thickness and O2 pressure, which satisfies the high capacity in the air with a low O2 partial pressure. The electrode with three-layers porosity distribution (TLE) has the highest specific capacity among the non-uniform porosity distributions, and the specific capacity increases from 14 to 56% compared to FE as the electrode thickness increases from 100 to 500 μm. In addition, the specific capacity of UTE (1224 mAh g−1) is more than 5 times higher than that of FE at 0.5 mA cm−2. The specific capacities corresponding to the three electrode structures are ranked as PWE>UTE-FE>TLE-FE, and the PWE shows more than 0.8- and 8-fold increases in specific capacity compared with TLE and FE at 0.5 mA cm−2, respectively. Therefore, this study contributes to the design and optimization of electrode structures to improve the areal capacity and energy density of Li-O2 batteries.

Nanoarchitectonics of the cathode to improve the reversibility of Li-O2 batteries.

The strategic design of the cathode is a critical feature for high-performance and long-lasting reversibility of an energy storage system. In particular, the round-trip efficiency and cycling performance of nonaqueous lithium–oxygen batteries are governed by minimizing the discharge products, such as Li2O and Li2O2. Recently, a metal–organic framework has been directly pyrolyzed into a carbon frame with controllable pore volume and size. Furthermore, selective metallic catalysts can also be obtained by adjusting metal ions for outstanding electrochemical reactions. In this study, various bimetallic zeolitic imidazolate framework (ZIF)-derived carbons were designed by varying the ratio of Zn to Co ions. Moreover, carbon nanotubes (CNTs) are added to improve the electrical conductivity further, ultimately leading to better electrochemical stability in the cathode. As a result, the optimized bimetallic ZIF–carbon/CNT composite exhibits a high discharge capacity of 16,000 mAh·g−1, with a stable cycling performance of up to 137 cycles. This feature is also beneficial for lowering the overpotential of the cathode during cycling, even at the high current density of 2,000 mA·g−1.

Recent progress in cathode catalyst for nonaqueous lithium oxygen batteries: a review

Recent progress in cathode catalyst for nonaqueous lithium oxygen batteries: a review

Atomically dispersed transition metal-N4 doped graphene as a LixOy nucleation site in nonaqueous lithium-oxygen batteries

Focusing on the catalytic mechanism of graphene with the atomically dispersed transition metal-N4 dispersed in nonaqueous lithium-oxygen battery, the adsorption models of key intermediates LixOy on the TM-N4 doped graphene surface are established by density functional theory (DFT) calculations. The nucleation and decomposition processes of Li2O2 are elucidated. Both of the charge transfer and electronic hybridization between TM-3d and O-2p orbitals influence the adsorption energies of key intermediates LixOy on the TM-N4 doped graphene surface. A greater adsorption energy usually corresponds to a greater TM atomic number. The adsorption energies of LiO2, Li3O4 and Li4O4 are the linear functions of the adsorption energy of Li2O2. The initial ORR processes on the Mn-N4, Fe-N4, Co-N4 doped graphene surfaces follow the two-electron reaction pathway, while the initial ORR processes on the Ni-N4 and Cu-N4 doped graphene surfaces might follow both of the two-electron and four-electron reaction pathways. The Co-N4 doped graphene possesses the overpotentials of 0.69 V for ORR and 0.92 V for OER, showing the optimal catalytic activity.

Ab Initio Exploration of Energetically and Kinetically Favorable ORR Activity on a 1T-ZrO2 Monolayer for a Nonaqueous Lithium-Oxygen Battery.

Herein, we explore the potential applications of the experimentally synthesized ZrO2 monolayer as the cathode catalyst for nonaqueous lithium-oxygen batteries. First, we show that a new peroxide-like adsorption geometry is the most stable configuration for LiO2, which is distinct from the previously known O-Li-O triangular geometry. The proposed most stable adsorption configuration is because the Zr atoms in the substrate play a critical role in stabilizing the LiO2 cluster. Second, our ab initio calculations indicate that both the ORR and OER catalytic activities are most likely to adopt the four-electron mechanism with a considerably low overpotential of only 0.44 and 0.76 V, respectively. Finally, we show that the adsorption energy of Li2O2 is a good descriptor for both ORR and OER catalytic activities, and weak Li2O2 adsorption behavior is positively related to low overpotentials and satisfactory catalytic performance.

Direct Visualization of Dynamic Mobility of Li2O2 in Li-O2 Batteries: A Differential Interference Microscopy Study.

The reversibility and the discharge/charge performance in nonaqueous lithium-oxygen (Li-O2) batteries are critically dependent on the kinetics of interfacial reactions. However, the interfacial reaction dynamic behaviors, especially the quantitative analysis, are still far from deep understanding. Using the method of laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), we monitored the Li-O2 interfacial reaction and in situ traced the Li2O2 migration processes promoted by the solution catalyst. Different dynamic behaviors exist when regulating the concentration of the redox mediator. Quantitative analysis of the discharged Li2O2 particles shows high mobility at the early discharge stage and decayed motion in the subsequent process, indicating the solution-mediated pathway participating Li2O2 formation in the low-concentration redox mediator addition, while particles/aggregates confined into the amorphous film demonstrate simultaneous solution and surface route-mediated pathway participation in the high-concentration case. These distinctive observations of Li2O2 formation and decomposition processes present the advantage of LCM-DIM to fundamentally understand the dynamic evolution in Li-O2 batteries.

Coupling Water-Proof Li Anodes with LiOH-Based Cathodes Enables Highly Rechargeable Lithium-Air Batteries Operating in Ambient Air.

Realizing an energy‐dense, highly rechargeable nonaqueous lithium–oxygen battery in ambient air remains a big challenge because the active materials of the typical high‐capacity cathode (Li2O2) and anode (Li metal) are unstable in air. Herein, a novel lithium–oxygen full cell coupling a lithium anode protected by a composite layer of polyethylene oxide (PEO)/lithium aluminum titanium phosphate (LATP)/wax to a LiOH‐based cathode is constructed. The protected lithium is stable in air and water, and permits reversible, dendrite‐free lithium stripping/plating in a wet nonaqueous electrolyte under ambient air. The LiOH‐based full cell reaction is immune to moisture (up to 99% humidity) in air and exhibits a much better resistance to CO2 contamination than Li2O2, resulting in a more consistent electrochemistry in the long term. The current approach of coupling a protected lithium anode with a LiOH‐based cathode holds promise for developing a long‐life, high‐energy lithium–air battery capable of operating in the ambient atmosphere.

Recent progress in the function of redox mediators on the electrode/electrolyte interfaces of lithium–oxygen batteries

The nonaqueous lithium–oxygen batteries have attracted considerable interest because of the ultrahigh theoretical capacity. However, the overpotential and cyclability issue of lithium–oxygen battery caused by interfacial issue limits its commercialization. To overcome these challenges, redox mediators, which are capable of charge transport on the electrode/electrolyte interfaces, are introduced to lithium–oxygen batteries to reduce overpotential. This review provides a detailed summary of the interfacial reaction mechanism and the influence of redox mediators on the electrode/electrolyte interfaces. Researches on suppressing redox mediators’ shuttle effect are also beneficial to enhance the electrochemical performance of lithium–oxygen batteries.

Modeling Studies of the Discharge Performance of Li-O2 Batteries with Different Cathode Open Structures

A two-dimensional (2D) transient model is proposed to explore the effect of cathode open structure on the discharge performance of the non-aqueous lithium-oxygen (Li-O2) batteries. It is found that decreasing the cathode open hole width (W hole) enhances the O2 transport ability in the electrode, making O2 concentration and lithium peroxide (Li2O2) deposit uniformly distributed within the electrode. This is conducive to reducing the concentration polarization and extending the discharge capacity of the Li-O2 batteries. The cathode open structure with W hole = 0.2 mm is regarded as the optimized open mode (OOM) as W hole = 0.2 mm gives the battery superior discharge performance, and further reduction of W hole will not increase the battery discharge capacity significantly. The Li-O2 battery with OOM has a pronounced increase in the discharge capacity under both pure O2 and air environments. The battery discharge capacity promotion by OOM is more remarkable if using DMSO electrolyte in the air environment and at a high current density of 4.0 A m−2. Therefore, the optimization of the cathode open structure is an effective way to improve the discharge performance of the Li-O2 batteries, especially operating in a low O2 environment.

Boosting the electrocatalytic activity of hollow NiCo layered double hydroxides nanocages via a self-regulating support effect: A highly efficient oxygen electrode for lithium-oxygen batteries

Surface engineering has been considered as one of the most useful strategies to enhance the activities of catalysts. However, conventional surface regulations usually require high cost and complicated chemical or physical processes, which restrict their practical applications. Herein, a zeolitic imidazolate framework-67 (ZIF-67) precursor is anchored first on Ni foam substrate, and then a hollow NiCo layered double hydroxides (NiCo-LDHs) nanocage is generated through a simple internal phase transition reaction. It is illustrated that with the self-regulating of Ni foam, more unsaturated metals sites and oxygen vacancy are created in the self-regulating NiCo-LDHs, which are key factors in improving the catalytic activities and durability. The self-regulating NiCo-LDHs electrode is used as cathode in nonaqueous lithium-oxygen (Li-O2) battery, and the battery exhibits a high initial capacity (26853 mAh·g@200 mA·g−1), high rate capability (upto 2000 mA·g−1), low overpotential (1.07 V), and long cycle life (upto 500 h). This work opens a facile direction to fabricate highly efficient electrocatalytic material through optimizing the electrode support effect.

Strategies with Functional Materials in Tackling Instability Challenges of Non-aqueous Lithium-Oxygen Batteries

The instabilities of the battery including cathode corrosion/passivation, shuttling effect of the redox mediators, Li anode corrosion, and electrolyte decomposition are major barriers toward the practical implementation of lithium-oxygen(Li-O2) batteries. Functional materials offer great potential in high performance Li-O2 batteries owing to their functional tailorability of chemical modification for alleviating side reactions and improving catalysis activity, well-defined properties for discharge products storage, and fast mass and electron transfer paths. In this review, instability problems of non-aqueous Li-O2 batteries and recent studies related to the functional materials in tackling the instability issues from rational cathode construction, inhibition of redox mediators(RMs) shuttling, anode protection and novel electrolyte design are illustrated. Future research directions to overcome the critical issues are also proposed for this promising battery technology. The instability issues and the related strategies with functional materials based on the comprehensive consideration of all battery components proposed in this review provide the systematic, deep understanding and rational design of functional materials for Li-O2 batteries, which is beneficial to achieving the practical Li-O2 batteries.

Mechanism for Preserving Volatile Nitrogen Dioxide and Sustainable Redox Mediation in the Nonaqueous Lithium–Oxygen Battery

Excessive overpotential during charging is a major hurdle in lithium-oxygen (Li-O2) battery technology. NO2-/NO2 redox mediation is an efficient way to substantially reduce the overpotential and to enhance oxygen efficiency and cycle life by suppressing parasitic reactions. Considering that nitrogen dioxide (NO2) is a gas, it is quite surprising that NO2-/NO2 redox reactions can be sustained for a long cycle life in Li-O2 batteries with such an open structure. A detailed study with in situ differential electrochemical mass spectrometry (DEMS) elucidated that NO2 could follow three reaction pathways during charging: (1) oxidation of Li2O2 to evolve oxygen, (2) vaporization, and (3) conversion into NO3-. Among the pathways, Li2O2 oxidation occurs exclusively in the presence of Li2O2, which suggests that NO2 has high reactivity to Li2O2. At the end of the charging process, most of the volatile oxidized couple (NO2) is stored by conversion to a stable third species (NO3-), which is then reused for producing the reduced couple (NO2-) in the next cycle. The dominant reaction of Li2O2 oxidation involves the temporary storage of NO2 as a stable third species during charging, which is an innovative way for preserving the volatile redox couple, resulting in a sustainable redox mediation for a high-performance Li-O2 battery.

A Novel Cr2O3/MnO2-x Electrode for Lithium-Oxygen Batteries with Low Charge Voltage and High Energy Efficiency.

A high energy efficiency, low charging voltage cathode is of great significance for the development of non-aqueous lithium-oxygen batteries. Non-stoichiometric manganese dioxide (MnO2-x) and chromium trioxide (Cr2O3) are known to have good catalytic activities for the discharging and charging processes, respectively. In this work, we prepared a cathode based on Cr2O3 decorated MnO2-x nanosheets via a simple anodic electrodeposition-electrostatic adsorption-calcination process. This combined fabrication process allowed the simultaneous introduction of abundant oxygen vacancies and trivalent manganese into the MnO2-x nanosheets, with a uniform load of a small amount of Cr2O3 on the surface of the MnO2-x nanosheets. Therefore, the Cr2O3/MnO2-x electrode exhibited a high catalytic effect for both discharging and charging, while providing high energy efficiency and low charge voltage. Experimental results show that the as-prepared Cr2O3/MnO2-x cathode could provide a specific capacity of 6,779 mA·h·g−1 with a terminal charge voltage of 3.84 V, and energy efficiency of 78%, at a current density of 200 mA·g−1. The Cr2O3/MnO2-x electrode also showed good rate capability and cycle stability. All the results suggest that the as-prepared Cr2O3/MnO2-x nanosheet electrode has great prospects in non-aqueous lithium-oxygen batteries.

Fabrication of single-ion conducting polymer-coated separators and their application in nonaqueous Li-O2 batteries

Nonaqueous lithium-oxygen (Li-O2) batteries have attracted increasing attention as potential candidates for next-generation batteries due to their significantly high theoretical energy densities. However, they are still in their infancy due to numerous problems. In this study, a cross-linked single-ion conducting polymer network with a highly delocalized anionic group was coated onto a thin commercial polyethylene membrane separator via a facile UV polymerization method. The resulting polymer coating improves the electrolyte wettability and suppresses the diffusion of anionic species across the separator. The effect of the polymer modification of the separator on the electrochemical properties of nonaqueous Li-O2 cells was investigated. A facile modification method for a commercial polyethylene membrane separator using a cross-linked single-ion conducting polymer network with a highly delocalized anionic group was developed. A cross-linker, poly(ethylene glycol) diacrylate, and a delocalized anionic monomer, lithium (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide, were used to modify the surface of the polyethylene separator via UV-initiated polymerization. The resulting polymer coating improves the electrolyte wettability and suppresses the diffusion of anionic species across the separator. The effect of the polymer modification of the separator on the electrochemical properties of nonaqueous Li-O2 cells was investigated.

Single-side functionalized graphene as promising cathode catalysts in nonaqueous lithium-oxygen batteries.

High-performance cathode catalysts are always desirable for nonaqueous lithium-oxygen (Li-O2) batteries. Using density functional theory calculations, the structural, electronic, and magnetic properties of SSX-Gr with different C/X ratios (X = H or F) are systematically studied. Then, a detailed mechanism on the dissociation of O2 and the migration of Li on the SSX-Gr is revealed, based on which C6X and C8X are confirmed as the potential candidates as cathode catalysts. The studies on reaction pathways suggest that the four-electron pathway is the more possible catalytic pathway for the selected SSX-Gr. The free energy diagrams for discharging and charging processes catalyzed by SSX-Gr reveal that C6F exhibits the highest application potential due to its considerably low oxygen reduction overpotential (0.83 V) and oxygen evolution overpotential (1.47 V). The extra spins induced by single-side functionalization endow graphene with the electrocatalytic activity.

Porous hollow ZnCo2S4 nanosheet arrays derived from metal-organic framework as efficient cathode for lithium oxygen batteries

Rechargeable non-aqueous lithium oxygen batteries (LOBs) have attracted extensive attention as the most promising next-generation battery technologies due to their extremely high theoretical energy density. However, their practical applications are hampered by sluggish reaction kinetics and severe parasitic reactions, resulting from the insulating and insoluble discharge product-Li2O2. Herein, self-standing ZnCo2S4 nanosheet arrays derived from metal-organic framework (MOF) via low-temperature solvothermal sulfuration method, are fabricated as efficient cathode for LOBs. The hollow structure of ZnCo2S4 nanosheet formed during sulfuration provides more catalytic sites and alleviates stress during repeated discharge/charge progress, while three-dimensional (3D) porous architecture inheriting from MOF shortens the transportation pathway of Li+ and O2 in electrolyte. Compared with pure CoS derived from Co-MOF, more Co3+ exposes on ZnCo2S4 surface due to the introduction of Zn, enhancing the catalytic activity distinctly. Benefitting from the bifunctional catalytic performance, the ZnCo2S4 cathode exhibits an extremely high initial discharge capacity of 9505 mAh g−1 at 100 mA g−1. Additionally, it also achieves a smaller overpotential of 1.02 V under a cutoff capacity of 1000 mAh g−1 and a longer cycle life of 90 cycles at 100 mA g−1. This work provides new insights into designing efficient bifunctional catalyst for LOBs.

Challenges and Strategy on Parasitic Reaction for High‐Performance Nonaqueous Lithium–Oxygen Batteries

AbstractThe soaring demands for large‐scale energy storage devices have triggered great interest in nonaqueous lithium–oxygen batteries (LOBs), the most promising next‐generation rechargeable batteries due to their extremely high energy density, low cost, and environmental friendliness. However, serious parasitic reactions give rise to continuous consumption of cell components and accumulation of indissoluble side products, resulting in high overpotential, low rate capability, and especially limited cycle life, which hinder the commercial application of LOBs. This review focuses on comprehensively understanding the possible parasitic reactions involved at the cathode, anode, and electrolyte engendered by reactive oxygen species, impurity gasses, and singlet oxygen, while other factors that destabilize batteries such as Li dendrites, high potential, and incompatibility of cell components are also discussed. Furthermore, the corresponding strategies to inhibit or eliminate parasitic reactions and enhance the cycle stability are elaborated from the perspectives of composition regulation, microstructural design, and alternative components. It should be emphasized that the introduction of dual redox mediators and singlet quencher is crucial to achieve efficient LOBs with high capacity and prolonged cycle life. Finally, perspectives on suppressing parasitic reaction are proposed with the purpose of providing inspiration in designing stable LOBs for practical applications.