Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions

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 (MnO_2-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 MnO_2-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 MnO_2-x nanosheets, with a uniform load of a small amount of Cr₂O₃ on the surface of the MnO_2-x nanosheets. Therefore, the Cr₂O₃/MnO_2-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/MnO_2-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/MnO_2-x electrode also showed good rate capability and cycle stability. All the results suggest that the as-prepared Cr₂O₃/MnO_2-x nanosheet electrode has great prospects in non-aqueous lithium-oxygen batteries.

Critical Advances in Ambient Air Operation of Nonaqueous Rechargeable Li-Air Batteries

Over the past few years, great attention has been given to nonaqueous lithium-air batteries owing to their ultrahigh theoretical energy density when compared with other energy storage systems. Most of the research interest, however, is dedicated to batteries operating in pure or dry oxygen atmospheres, while Li-air batteries that operate in ambient air still face big challenges. The biggest challenges are H₂ O and CO₂ that exist in ambient air, which can not only form byproducts with discharge products (Li₂ O₂ ), but also react with the electrolyte and the Li anode. To this end, recent progress in understanding the chemical and electrochemical reactions of Li-air batteries in ambient air is critical for the development and application of true Li-air batteries. Oxygen-selective membranes, multifunctional catalysts, and electrolyte alternatives for ambient air operational Li-air batteries are presented and discussed comprehensively. In addition, separator modification and Li anode protection are covered. Furthermore, the challenges and directions for the future development of Li-air batteries are presented.

A novel strategy for improving performance of lithium-oxygen batteries

Although the theoretical energy density of lithium-oxygen batteries is extremely high, pulverization of lithium metal anode obviously influences batteries cycling performance. In this work, the cathode was coated with a membrane to protect the lithium anode from moisture attacking and avoid the pulverization. The membrane is composed of polyethylene oxide and poly tetra fluoroethylene, which improves the cycle life of the lithium-oxygen batteries cycles to 230 times, with a limited specific capacity of 1000 mAh·g^-1, at a current density of 100 mA·g^-1. Furthermore, the batteries perform stable charge and discharge cycles for 55 times in the air atmosphere, with the relative humidity greater than 50%. It demonstrates this strategy provides a new direction for the development of high-performance lithium-oxygen batteries.

Impact of a Gold Nanocolloid Electrolyte on Li2O2 Morphology and Performance of a Lithium-Oxygen Battery

Aprotic lithium-oxygen batteries currently suffer from poor cyclic stability and low achievable energy density. Herein, gold nanoparticles capped with mercaptosuccinic acid are dispersed in 1.0 M LiClO₄/dimethyl sulfoxide (DMSO) as a novel electrolyte for lithium-oxygen batteries. Morphological and electrochemical analyses indicate that film-like amorphous lithium peroxide is formed using the gold nanocolloid electrolyte instead of bulk crystals in battery discharging, which apparently increases the conductivity and accelerates the decomposition kinetics of discharge products in recharging, accompanied by the release of incorporated gold nanoparticles with the decomposition of lithium peroxide into the electrolyte. Experiments and theoretical calculations further demonstrate that the suspended gold nanoparticles in the electrolyte can adsorb some intermediates generated by an oxygen reduction reaction, which effectively alleviates the cleavage of the electrolyte and impedes the corrosion of the lithium anode. As a result, the life span of lithium-oxygen batteries is dramatically increased from 55 to 438 cycles, and the rate performance and full-discharge capacity are also massively enhanced. The battery failure is attributed to the degradation of gold nanocolloid electrolytes, and further studies on improvement of colloid stability during battery cycling are underway.

Tetramethylpyrazine: an electrolyte additive for high capacity and energy efficiency lithium–oxygen batteries

Lithium–oxygen batteries have attracted great attention in recent years owing to their extremely high theoretical energy density, however, factors such as low actual capacity and poor rate performance hinder the practical application of lithium–oxygen batteries. In this work, a novel electrolyte additive, tetramethylpyrazine (TMP), is introduced into an electrolyte system to enhance the electrochemical performance of the lithium–oxygen batteries. TMP does not undergo its own redox reaction within the charge–discharge voltage range, which will not affect the electrochemical stability of the electrolyte. The results show that the addition of TMP can increase the reduction current of oxygen, which will promote the ORR process, and with an optimal TMP content (50 mM), the cell shows a high discharge capacity of 5712.3 mA h g⁻¹ at 0.1 mA cm⁻². And its rate capability is almost doubled compared with the system without TMP additive at a large current density of 1 mA cm⁻². Further analysis by SEM and XRD reveals that the addition of TMP can reduce the formation of by-products and promote the solution growth of large-size Li₂O₂ particles to achieve a large discharge capacity. This approach could provide a new idea for improving the electrochemical performance of lithium–oxygen batteries.

TMP has a strong interaction with Li⁺, which promotes the solution mechanism of Li₂O₂, thereby increasing the discharge capacity.

In Situ Realization of Water‐Mediated Interfacial Processes at Nanoscale in Aprotic Li–O2 Batteries

A fundamental understanding of the remarkable impact of water on the interfacial processes of lithium–oxygen (Li–O2) reactions is of great significance for the practical application of Li–O2 batteries. However, clarifying the growth pathway and surface dynamics of active products regulated by water at the nanoscale is still at a preliminary stage. Here, the interfacial evolution of cathode processes mediated by water in Li–O2 batteries is successfully revealed by using in situ atomic force microscopy. Under the regulation of additive water, the morphology of discharge product Li2O2 is changed from a toroidal shape to a lamellar one with water content increasing, by contrast, the latter one shows a lower decomposition potential with faster dynamics upon charging. Moreover, real‐time visualization directly shows that inducing water into the DMSO‐based electrolyte can switch the pathway of Li2O2 nucleation from a surface‐mediated mechanism to solution‐mediated mechanism, which in turn affects product distribution and battery performance. Furthermore, it is found that the applied current density and additive water can antagonistically impact the interfacial behavior. The insights into the effect of water on the nucleation modes and evolution processes of Li2O2 provides a deeper understanding of the interfacial reactions in Li–O2 batteries.

Porous Materials Applied in Nonaqueous Li-O2 Batteries: Status and Perspectives

Porous materials possessing high surface area, large pore volume, tunable pore structure, superior tailorability, and dimensional effect have been widely applied as components of lithium-oxygen (Li-O₂ ) batteries. Herein, the theoretical foundation of the porous materials applied in Li-O₂ batteries is provided, based on the present understanding of the battery mechanism and the challenges and advantageous qualities of porous materials. Furthermore, recent progress in porous materials applied as the cathode, anode, separator, and electrolyte in Li-O₂ batteries is summarized, together with corresponding approaches to address the critical issues that remain at present. Particular emphasis is placed on the importance of the correlation between the function-orientated design of porous materials and key challenges of Li-O₂ batteries in accelerating oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) kinetics, improving the electrode stability, controlling lithium deposition, suppressing the shuttle effect of the dissolved redox mediators, and alleviating electrolyte decomposition. Finally, the rational design and innovative directions of porous materials are provided for their development and application in Li-O₂ battery systems.

Synergistic Effect of Binary Electrolyte on Enhancement of the Energy Density in Li-O2 Batteries

Enhancement of the discharge capacity of lithium-oxygen batteries (LOBs) while maintaining a high cell voltage is an important challenge to overcome to achieve an ideal energy density. Both the cell voltage and discharge capacity of an LOB could be controlled by employing a binary solvent electrolyte composed of dimethyl sulfoxide (DMSO) and acetonitrile (MeCN), whereby an energy density 3.2 times higher than that of the 100 vol % DMSO electrolyte was obtained with an electrolyte containing 50 vol % of DMSO. The difference in the solvent species that preferentially solvates Li⁺ and that which controls the adsorption-desorption equilibrium of the discharge reaction intermediate, LiO₂, on the cathode/electrolyte interface provides these unique properties of the binary solvent electrolyte. Combined spectroscopic and electrochemical analysis have revealed that the solvated complex of Li⁺ and the environment of the cathode/electrolyte interface were the determinants of the cell voltage and discharge capacity, respectively.

Surface Mechanism of Catalytic Electrodes in Lithium-Oxygen Batteries: How Nanostructures Mediate the Interfacial Reactions

The use of catalysts is the key to boost electrode reactions in lithium-oxygen (Li-O2) batteries. In-depth understanding of the nanoscale catalytic effect at electrode/electrolyte interfaces is of great significance for guiding a design of functionally optimized catalyst. Here, using electrochemical atomic force microscopy, we present the real-time imaging of interfacial evolution on nanostructured Au electrodes in a working battery, revealing that the nanostructure of Au is directly related to the catalytic activity toward oxygen reduction reaction (ORR)/oxygen evolution reaction (OER). In situ views show that nanoporous Au with a size of ∼14 nm for ligaments and ∼5 nm for nanopores promote the nucleation and growth of discharge product Li2O2 with large size at a high discharge voltage, yet densely packed Au nanoparticles with a diameter of ∼15 nm could catalyze Li2O2 to fully decompose via the top-bottom approach at a low charge potential. In addition, the difference in the nucleation potential of Li2O2 on the electrode with hybrid nanostructures could result in an uneven distribution of discharge products, which is alleviated at a large discharge rate and the capacity of the battery is improved significantly. These observations provide deep insights into the mechanisms of Li-O2 interfacial reaction catalyzed by nanostructured catalysts and strategies for improving Li-O2 batteries.

A Bifunctional Photo-Assisted Li-O2 Battery Based on a Hierarchical Heterostructured Cathode

Photo-assisted charging is considered an effective approach to reducing the overpotential in lithium-oxygen (Li-O₂ ) batteries. However, the utilization of photoenergy during the discharge process in a Li-O₂ system has been rarely reported, and the functional mechanism of such a process remains unclear. Herein, a novel bifunctional photo-assisted Li-O₂ system is established by employing a hierarchical TiO₂ -Fe₂ O₃ heterojunction, in which the photo-generated electrons and holes play key roles in reducing the overpotential in the discharging and charging processes, respectively. Moreover, the morphology of the discharge product (Li₂ O₂ ) can be modified via the dense surface electrons of the cathode under illumination, resulting in promoted decomposition kinetics of Li₂ O₂ during the charging progress. Accordingly, the output and input energies of the battery can be tuned by illumination, giving an ultralow overpotential of 0.19 V between the charge and discharge plateaus with excellent cyclic stability (retaining a round-trip efficiency of ≈86% after 100 cycles). The investigation of the bifunctional photo-assisted process presented here provides significant insight into the mechanism of the photo-assisted Li-O₂ battery and addresses the overpotential bottleneck in this system.

Li-CO2 and Na-CO2 Batteries: Toward Greener and Sustainable Electrical Energy Storage

Metal-CO₂ batteries, especially Li-CO₂ and Na-CO₂ batteries, offer a novel and attractive strategy for CO₂ capture as well as energy conversion and storage with high specific energy densities. However, some scientific issues and challenges existing restrict their practical applications. Here, recent progress of crucial reaction mechanisms on cathodes in Li-CO₂ and Na-CO₂ batteries are summarized. The detailed reaction pathways can be modified by operation conditions, electrolyte compositions, and catalysts. Besides, specific discussions from aspects of catalyst design, stability of electrolytes, and anode protection are presented. Perspectives of several innovative directions are also put forward. This review provides an intensive understanding of Li-CO₂ and Na-CO₂ batteries and gives a useful guideline for the practical development of metal-CO₂ batteries and even metal-air batteries.

Rationalizing the Effect of Oxygen Vacancy on Oxygen Electrocatalysis in Li-O2 Battery

Albeit the effectiveness of surface oxygen vacancy in improving oxygen redox reactions in Li-O₂ battery, the underpinning reason behind this improvement remains ambiguous. Herein, the concentration of oxygen vacancy in spinel NiCo₂ O₄ is first regulated via magnetron sputtering and its relationship with catalytic activity is comprehensively studied in Li-O₂ battery based on experiment and density functional theory (DFT) calculation. The positive effect posed by oxygen vacancy originates from the up shifted antibond orbital relative to Fermi level (E_f ), which provides extra electronic state around E_f , eventually enhancing oxygen adsorption and charge transfer during oxygen redox reactions. However, with excessive oxygen vacancy, the negative effect emerges because the metal ions are mostly reduced to low valence based on the electrical neutral principle, which not only destabilizes the crystal structure but also weakens the ability to capture electrons from the antibond orbit of Li₂ O₂ , leading to poor catalytic activity for oxygen evolution reaction (OER).

Fabrication of carbon cloth supporting MnO x and its application in Li-O2 batteries

High-efficiency and low-cost electrocatalysts are generally believed to be the critical factor and have been highly researched to catalyze the oxygen reduction reaction (ORR) during the operation of Li-O₂ battery (LOB). The catalysts with better ORR performance are essential for high-performance LOBs. Herein, a binder-free MnO _x @carbon cloth cathode composed of Mn₃O₄ nanoparticles and Mn₂O₃ nanosheets were directly synthesized on the carbon cloth by electrodeposition and subsequently heat treatment at different temperature (from 200 °C to 400 °C). With the increase of temperature, the Mn₃O₄ nanospheres gradually transformed into Mn₂O₃ nanosheets. The MnO _x obtained at 350 °C exhibited the best ORR performance. And MnO _x -350 °C could operate more than 80 cycles at 340 mA g^-1 with a limiting specific capacity of 1000 mAh g^-1, and its first discharge specific capacity could nearly achieve 8000 mAh g^-1 at 200 mA g^-1.

A 3D free-standing Co doped Ni2P nanowire oxygen electrode for stable and long-life lithium-oxygen batteries

Exploring oxygen electrodes with superior bifunctional catalytic activity and suitable architecture is an effective strategy to improve the performance of lithium-oxygen (Li-O₂) batteries. Herein, the internal electronic structure of Ni₂P is regulated by heteroatom Co doping to improve its catalytic activity for oxygen redox reactions. Meanwhile, magnetron sputtering N-doped carbon cloth (N-CC) is used as a scaffold to enhance the electrical conductivity. The deliberately designed Co-Ni₂P on N-CC (Co-Ni₂P@N-CC) with a typical 3D interconnected architecture facilitates the formation of abundant solid-liquid-gas three-phase reaction interfaces inside the architecture. Furthermore, the rational catalyst/substrate interfacial interaction is capable of inducing a solvation-mediated pathway to form toroidal-Li₂O₂. The results show that the Co-Ni₂P@N-CC based Li-O₂ battery exhibits an ultra-low overpotential (0.73 V), enhanced rate performance (4487 mA h g^-1 at 500 mA g^-1) and durability (stable operation over 671 h). The pouch-type battery based on the Co-Ni₂P@N-CC flexible electrode runs stably for 581 min in air without obvious voltage attenuation. This work verifies that heterogeneous atom doping and interface interaction can remarkably strengthen the performance of Li-O₂ cells and thus pave new avenues towards developing high-performance metal-air batteries.

Heterostructured NiS2/ZnIn2S4 Realizing Toroid-like Li2O2 Deposition in Lithium-Oxygen Batteries with Low-Donor-Number Solvents

The aprotic lithium-oxygen (Li-O₂) battery has triggered tremendous efforts for advanced energy storage due to the high energy density. However, realizing toroid-like Li₂O₂ deposition in low-donor-number (DN) solvents is still the intractable obstruction. Herein, a heterostructured NiS₂/ZnIn₂S₄ is elaborately developed and investigated as a promising catalyst to regulate the Li₂O₂ deposition in low-DN solvents. The as-developed NiS₂/ZnIn₂S₄ promotes interfacial electron transfer, regulates the adsorption energy of the reaction intermediates, and accelerates O-O bond cleavage, which are convincingly evidenced experimentally and theoretically. As a result, the toroid-like Li₂O₂ product is achieved in a Li-O₂ battery with low-DN solvents via the solvation-mediated pathway, which demonstrates superb cyclability over 490 cycles and a high output capacity of 3682 mA h g^-1. The interface engineering of heterostructure catalysts offers more possibilities for the realization of toroid-like Li₂O₂ in low-DN solvents, holding great promise in achieving practical applications of Li-O₂ batteries as well as enlightening the material design in catalytic systems.

Inhibition of Discharge Side Reactions by Promoting Solution-Mediated Oxygen Reduction Reaction with Stable Quinone in Li-O2 Batteries

Aprotic lithium-oxygen (Li-O₂) batteries with an ultrahigh theoretical energy density have great potential in rechargeable power supply, while their application still faces several challenges, especially poor cycle stability. To solve the problems, one of the effective strategies is to inhibit the generation of the LiO₂ intermediate produced via a surface-mediated oxygen reduction reaction (ORR) pathway, which is an important species inducing byproduct generation and low cell cyclic stability. Herein, a series of quinones and solid materials serve as the solution-mediated and surface-mediated ORR catalysts, and it was found that the generation of LiO₂ and byproducts from solid catalysts was inhibited by quinones. Among the studied quinones, benzo[1,2-b:4,5-b']dithiophene-4,8-dione, a quinone molecule with the advantage of a highly symmetrical planar and conjugated structure and without α-H, exhibits high redox potential, diffusion coefficient, and electrochemical stability, and consequently the best ORR activities and the capability to inhibit byproduct generation. It indicated that the increase of the solution-mediated ORR pathway plays an important role in restraining the discharging side reaction, substantially improving cell cycle stability and capacity. This study provides the theoretical and experimental basis for better understanding the ORR process of Li-O₂ batteries.

Electrochemical Oxidation of Li2O2 Surface-Doped with Li2CO3

Electrochemical oxidation of Li₂O₂, i.e., the charging reaction of the aprotic lithium-oxygen batteries (Li-O₂ batteries), is significantly influenced by its surface chemistry. Here, the surface species of Li₂CO₃, widely identified together with Li₂O₂ at the end of discharge, is investigated to understand its implication for the oxidation of Li₂O₂. In situ doping Li₂O₂ with various amounts of Li₂CO₃ has been obtained by reacting with CO₂ gas in a controlled way, and the electrochemical oxidation of the doped Li₂O₂ is studied with a quantitative differential electrochemical mass spectrometer (DEMS). Instead of a single charging potential plateau and one O₂ gas evolution stage for the pristine Li₂O₂, Li₂CO₃-doped Li₂O₂ exhibits two O₂/CO₂ gas evolution stages and three charging plateaus characterized with the larger overpotential for the initial and final stages. The conductivity of Li₂CO₃ dopant is invoked to explain the different oxidation behaviors of Li₂CO₃-doped Li₂O₂. The DEMS study of the electrochemical oxidation of isotope-labeled Li₂¹³CO₃ is also conducted to identify the origins of O₂ and CO₂ evolution during the oxidation of Li₂CO₃-doped Li₂O₂. The results reported here provide an improved understanding of the Li₂O₂ oxidation in the presence of parasitic Li₂CO₃ species and will contribute to the future development of Li-O₂ batteries.

Potassium Doping Facilitated Formation of Tunable Superoxides in Li2O2 for Improved Electrochemical Kinetics

Superoxide (O₂^-) species play a crucial role in determining the charge kinetics for aprotic lithium-oxygen (Li-O₂) batteries. However, the growth of O₂^--rich lithium peroxide (Li₂O₂) is challenging since O₂^- is thermodynamically unfavorable and unstable in an O₂ atmosphere. Herein, we reported the synthesis of defective Li₂O₂ with tunable O₂^- via K⁺ doping. The K⁺ dopants can successfully stabilize O₂^- species and induce the coordination of Li⁺ with O₂^-, leading to increased Li vacancies. Compared to the pristine Li₂O₂, the as-prepared defective Li₂O₂ can be charged at a lower overpotential in Li-O₂ batteries, which is ascribed to further increased Li vacancies contributed by the depotassiation process at the onset of the charge process. Our findings suggest a new strategy to better control O₂^- species in Li₂O₂ by K⁺ dopants and provide insights into the K⁺ effects on charge mechanism in Li-O₂ batteries.

Stabilization of binder-free vanadium oxide-based oxygen electrodes using Pd clusters for Li–O2 batteries

A stable binder-free carbon cloth supporting V₂O₅-Pd clusters was synthesized through hydrothermal and gas-phase-cluster beam deposition. The as-prepared binder-free electrode showed potential application in hybrid energy storage systems.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.

Hierarchical Mesoporous/Macroporous Co-Doped NiO Nanosheet Arrays as Free-Standing Electrode Materials for Rechargeable Li-O2 Batteries

Lithium-oxygen (Li-O₂) batteries have been widely recognized as appealing power systems for their extremely high energy density versus common Li-ion batteries. However, there are still lots of issues that need to be addressed toward the practical application. Here, free-standing Co-doped NiO three-dimensional nanosheets were prepared by a hydrothermal synthesis method and directly employed as the air-breathing cathode of the Li-O₂ battery. The morphological phenomenon and electrochemical performance of the as-prepared cathode material were characterized by high-resolution scanning electron microscopy, X-ray diffraction, cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy measurements. The Co-doped NiO electrode delivered a maximum discharge capacity of around 12 857 mA h g^-1 with a low overpotential (0.82 V) at 200 mA g^-1. Under upper-limit specific capacities of 500 mA h g^-1 at 400 mA g^-1, the Li-O₂ batteries exhibited a long cycle life of 165 cycles. Compared with the undoped NiO electrode, the Li-O₂ battery based on the Co-doped NiO cathode showed significantly higher oxygen reduction reaction and oxygen evolution reaction activities. This superior electrochemical performance is because of the partial substitution of Ni²⁺ in the NiO matrix by Co²⁺ to improve the p-type electronic conductivity of NiO. In addition, the morphology and specific surface area of NiO are affected by Co doping, which can expand the electrode-electrolyte contact area and lead to sufficient space for Li₂O₂ deposition. This approach harnesses the great potential of Co-doped NiO nanosheets for practical applications as advanced electrodes for rechargeable Li-O₂ batteries.

Pt/NiO Microsphere Composite as Efficient Multifunctional Catalysts for Nonaqueous Lithium-Oxygen Batteries and Alkaline Fuel Cells: The Synergistic Effect of Pt and Ni

Developing efficient and low-cost multifunctional electrocatalysts is important for electrochemical devices. In this work, a cost-effective Pt/NiO composite with very limited Pt loading (from 0.5 to 3%) was controllably synthesized through facile hydrothermal procedures. The composite demonstrated the improved catalytic performance as applied to the nonaqueous Li-O₂ batteries and the alkaline fuel cells. Regarding the alkaline fuel cells, 1% Pt/NiO composite gave rise to the best Pt distribution and thus exhibited the optimized electrochemical conductivity and properties as suggested by the significantly improved electrochemical reversibility. Meanwhile, the demonstrated 1% Pt/NiO composite presented high catalytic capability as electrode for Li-O₂ batteries, which allowed for much improved capacity utilization, high cycling stability, high initial capacity (2329 mAh/g), and no obvious voltage drop during cycling. Such multiple advantages of prepared composite electrode material offer new prospects and application as multifunctional electrocatalysts for both Li-O₂ batteries and alkaline fuel cells.

Heteroatom-Induced Electronic Structure Modulation of Vertically Oriented Oxygen Vacancy-Rich NiFe Layered Double Oxide Nanoflakes To Boost Bifunctional Catalytic Activity in Li-O2 Battery

NiFe-based transition metal oxide (NiFe-TMO) has been identified as an effective electrocatalyst for lithium-oxygen (Li-O₂) batteries due to its superior catalytic activity for oxygen evolution reaction. Improving the bifunctional catalytic ability of NiFe-TMO is essential for the further performance improvement of Li-O₂ batteries. Herein, we regulated the electronic structure of free-standing NiFe LDO nanosheets array via introducing foreign Co ion to improve its bifunctional catalytic activity in Li-O₂ batteries. Combined with well-designed electrode architecture and the deliberately modified surface electronic structure, this strategy markedly alleviates polarization problem in terms of low overpotential (0.98 V), and the discharge voltage within 110 cycles remains stable at 2.89 V without significant attenuation. This study illustrates an intimate connection between electronic structure engineering and catalytic activity optimization that is critical for the rational design of Li-O₂ batteries.

Recent Progress on Catalysts for the Positive Electrode of Aprotic Lithium-Oxygen Batteries †

Rechargeable aprotic lithium-oxygen (Li-O2) batteries have attracted significant interest in recent years owing to their ultrahigh theoretical capacity, low cost, and environmental friendliness. However, the further development of Li-O2 batteries is hindered by some ineluctable issues, such as severe parasitic reactions, low energy efficiency, poor rate capability, short cycling life and potential safety hazards, which mainly stem from the high charging overpotential in the positive electrode side. Thus, it is of great significance to develop high-performance catalysts for the positive electrode in order to address these issues and to boost the commercialization of Li-O2 batteries. In this review, three main categories of catalyst for the positive electrode of Li-O2 batteries, including carbon materials, noble metals and their oxides, and transition metals and their oxides, are systematically summarized and discussed. We not only focus on the electrochemical performance of batteries, but also pay more attention to understanding the catalytic mechanism of these catalysts for the positive electrode. In closing, opportunities for the design of better catalysts for the positive electrode of high-performance Li-O2 batteries are discussed.

The design of hollow PdO–Co3O4 nano-dodecahedrons with moderate catalytic activity for Li–O2 batteries

Hollow PdO–Co₃O₄ nano-dodecahedrons can stably cycle for more than 90 cycles with a low overpotential as an electrocatalyst for Li–O₂ batteries.