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

All-Solid-State Mg-Air Battery Enhanced with Free-Standing N-Doped 3D Nanoporous Graphene

Nitrogen (N) doping of graphene with a three-dimensional (3D) porous structure, high flexibility, and low cost exhibits potential for developing metal-air batteries to power electric/electronic devices. The optimization of N-doping into graphene and the design of interconnected and monolithic graphene-based 3D porous structures are crucial for mass/ion diffusion and the final oxygen reduction reaction (ORR)/battery performance. Aqueous-type and all-solid-state primary Mg-air batteries using N-doped nanoporous graphene as air cathodes are assembled. N-doped nanoporous graphene with 50-150 nm pores and ≈99% porosity is found to exhibit a Pt-comparable ORR performance, along with satisfactory durability in both neutral and alkaline media. Remarkably, the all-solid-state battery exhibits a peak power density of 72.1 mW cm-2 ; this value is higher than that of a battery using Pt/carbon cathodes (54.3 mW cm-2 ) owing to the enhanced catalytic activity induced by N-doping and rapid air breathing in the 3D porous structure. Additionally, the all-solid-state battery demonstrates better performances than the aqueous-type battery owing to slow corrosion of the Mg anode by solid electrolytes. This study sheds light on the design of free-standing and catalytically active 3D nanoporous graphene that enhances the performance of both Mg-air batteries and various carbon-neutral-technologies using neutral electrolytes.

Highly Stable Garnet Fe2 Mo3 O12 Cathode Boosts the Lithium-Air Battery Performance Featuring a Polyhedral Framework and Cationic Vacancy Concentrated Surface

Lithium-air batteries (LABs), owing to their ultrahigh theoretical energy density, are recognized as one of the next-generation energy storage techniques. However, it remains a tricky problem to find highly active cathode catalyst operating within ambient air. In this contribution, a highly active Fe₂ Mo₃ O₁₂ (FeMoO) garnet cathode catalyst for LABs is reported. The experimental and theoretical analysis demonstrate that the highly stable polyhedral framework, composed of FeO octahedrons and MO tetrahedrons, provides a highly effective air catalytic activity and long-term stability, and meanwhile keeps good structural stability. The FeMoO electrode delivers a cycle life of over 1800 h by applying a simple half-sealed condition in ambient air. It is found that surface-rich Fe vacancy can act as an O₂ pump to accelerate the catalytic reaction. Furthermore, the FeMoO catalyst exhibits a superior catalytic capability for the decomposition of Li₂ CO₃ . H₂ O in the air can be regarded as the main contribution to the anode corrosion and the deterioration of LAB cells could be attributed to the formation of LiOH·H₂ O at the end of cycling. The present work provides in-depth insights to understand the catalytic mechanism in air and constitutes a conceptual breakthrough in catalyst design for efficient cell structure in practical LABs.

RuO2-Incorporated Co3O4 Nanoneedles Grown on Carbon Cloth as Binder-Free Integrated Cathodes for Tuning Favorable Li2O2 Formation

Developing ideal Li-O₂ batteries (LOBs) requires the discharge product to have a large quantity, have large contact area with the cathode, and not passivate the porous surface after discharge, which put forward high requirement for the design of cathodes. Herein, combining the rational structural design and high activity catalyst selection, minor amounts of RuO₂-incorporated Co₃O₄ nanoneedles grown on carbon cloth are successfully synthesized as binder-free integrated cathodes for LOBs. With this unique design, plenty of electron-ion-oxygen tri-phase reaction interface is created, the side reaction from carbon is isolated, and oxygen reduction reaction/oxygen evolution reaction (OER) kinetics are significantly facilitated. Upon discharge, film-like Li₂O₂ is observed growing on the needle surface first and eventually ball-like Li₂O₂ particles form at each tip of the needle. The cathode surface remains porous after discharge, which is beneficial to the OER and is rare in the previous reports. The battery exhibits a high specific discharge capacity (7.64 mAh cm^-2) and a long lifespan (500 h at 0.1 mA cm^-2). Even with a high current of 0.3 mA cm^-2, the battery achieves a cycling life of 200 h. In addition, punch-type LOBs are fabricated and successfully operated, suggesting that the cathode material can be utilized in ultralight, flexible electronic devices.

Nanofibrous Cathode Catalysts with MoC Nanoparticles Embedded in N-Rich Carbon Shells for Low-Overpotential Li-CO2 Batteries

Li-CO₂ batteries with high theoretical energy densities are recognized as next-generation energy storage devices for addressing the range anxiety and environmental issues encountered in the field of electric transportation. However, cathode catalysts with unsatisfactory activity toward CO₂ absorption and reduction/evolution reactions hinder the development of Li-CO₂ batteries with desired specific capacities and sufficient cycle numbers. In this work, a multifunctional nanofibrous cathode catalyst that integrates N-rich carbon shells embedded with molybdenum carbide nanoparticles and multiwalled carbon nanotube cores was designed and prepared. The N-rich carbon shell could strengthen the absorption capacity of CO₂ and Li₂CO₃. The molybdenum carbide nanoparticles would improve the catalytic activity of both CO₂ reduction and evolution reactions. The carbon nanotube cores would provide an efficient network for electron transportation. The synergistic effect of the cathode catalysts enhances the electrochemical performance of Li-CO₂ batteries. A high cycling stability of more than 150 cycles at a current density of 250 mA g^-1 with a cutoff capacity of 1000 mAh g^-1 and a charge/discharge overpotential of less than 1.5 V is achieved. This work provides a feasible strategy for the design of a high-performance cathode catalyst for lithium-air batteries.

Construction of Co,N-Coordinated Carbon Dots for Efficient Oxygen Reduction Reaction

For the sake of the oxygen reduction reaction (ORR) catalytic performance, carbon dots (CDs) doped with metal atoms have accelerated their local electron flow for the past few years. However, the influence of CDs doped with metal atoms on binding sites and formation mechanisms is still uncertain. Herein, Co,N-doped CDs were facilely prepared by the low-temperature polymerization-solvent extraction strategy from EDTA-Co. The influence of Co doping on the catalytic performance of Co-CDs was explored, mainly in the following aspects: first, the pyridinic N atom content of Co-CDs significantly increased from 4.2 to 11.27 at% compared with the CDs, which indicates that the Co element in the precursor is advantageous in forming more pyridinic-N-active sites for boosting the ORR performance. Second, Co-CDs are uniformly distributed on the surface of carbon black (CB) to form Co-CDs@CB by the facile hydrothermal route, which can expose more active sites than the aggregation status. Third, the highest graphite N content of Co-CDs@CB was found, by limiting the current density of the catalyst towards the ORR. Composite nanomaterials formed by Co and CB are also used as air electrodes to manufacture high-performance zinc-air batteries. The battery has good cycle stability and realizes stable charges and discharges under different current densities. The outstanding catalytic activity of Co-CDs@CB is attributed to the Co,N synergistic effect induced by Co doping, which pioneer a new metal doping mechanism for gaining high-performance electrocatalysts.

A High-Energy-Density Magnesium-Air Battery with Nanostructured Polymeric Electrodes

The greenhouse emissions are biggest challenge of the present era. The renewable power sources are required to have characteristics of good charge capacity, energy density with proven charging discharging cycles for energy storage and applications. Mg-air batteries (MABs) are an alternative renewable power source due to their inexpensive cost. In particular, the previous reports presented the metal-air battery structure, with a specific energy overall output of 765 W h kg⁻¹. This paper is focused mainly on the MAB, which employed nanocomposite polymeric electrodes with a proven energy density of 545 W h kg⁻¹ and a charge capacity of 817 mA h g⁻¹ when electrolyzed at a cycling current density of 7 mA cm⁻².

Design and Development of Cathode Materials for Rechargeable Batteries

Over the past two decades, rechargeable Li-ion batteries (LIBs) have been the de facto standard power source for electronic devices [...]

Superdry poly(vinylidene fluoride-co-hexafluoropropylene) coating on a lithium anode as a protective layer and separator for a high-performance lithium-oxygen battery

In this study, a dense polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) coating is fabricated on a lithium (Li) anode sheet, which acts as a synergistic protective layer and electrolyte separator for Li-oxygen (Li-O₂) batteries. This thin coating is dried through slow solvent evaporation and vacuum drying methods. The solvent-free, dense PVDF-HFP coating has a thickness of 45 µm and can absorb 62% of electrolyte. The battery containing the PVDF-HFP coating demonstrates a maximum peak power density of 3 mW cm^-2, significantly higher than that of the battery with the PVDF coating (0.8 mW cm^-2) but lower than that without coating (equipped with a commercial glass fiber separator, 7.3 mW cm^-2). However, the PVDF-HFP coating enables the Li-O₂ battery to reach a capacity of 4400 mA h g^-1, much higher than that without the coating (glass fiber separator, 850 mA h g^-1). The symmetric Li-Li cells further confirm steady and low overpotentials using the anode coating at a high current density of 1.0 mA cm^-2, indicating stable Li plating/stripping process. The PVDF-HFP-coated battery has a longer cycling lifetime (1700 h) than those with the PVDF coating (120 h) and a glass fiber separator (670 h). The Raman spectra show that there are lithium compounds (mainly lithium hydroxide) and residual PVDF-HFP on the aged anode surface. The dense PVDF-HFP coating on the Li anode plays dual roles: it creates a strong protective layer for stabilizing the solid-electrolyte interface (in the solid phase), and acts as a separator for modulating the Li metal deposition and stripping behaviors in liquid electrolyte.

Carbon Tube-Based Cathode for Li-CO2 Batteries: A Review

Metal–air batteries are considered the research, development, and application direction of electrochemical devices in the future because of their high theoretical energy density. Among them, lithium–carbon dioxide (Li–CO₂) batteries can capture, fix, and transform the greenhouse gas carbon dioxide while storing energy efficiently, which is an effective technique to achieve “carbon neutrality”. However, the current research on this battery system is still in the initial stage, the selection of key materials such as electrodes and electrolytes still need to be optimized, and the actual reaction path needs to be studied. Carbon tube-based composites have been widely used in this energy storage system due to their excellent electrical conductivity and ability to construct unique spatial structures containing various catalyst loads. In this review, the basic principle of Li–CO₂ batteries and the research progress of carbon tube-based composite cathode materials were introduced, the preparation and evaluation strategies together with the existing problems were described, and the future development direction of carbon tube-based materials in Li–CO₂ batteries was proposed.

CoS2 Nanoparticles Anchored on MoS2 Nanorods As a Superior Bifunctional Electrocatalyst Boosting Li2 O2 Heteroepitaxial Growth for Rechargeable Li-O2 Batteries

Developing an excellent bifunctional catalyst is essential for the commercial application of Li-O₂ batteries. Heterostructures exhibit great application potential in the field of energy catalysis because of the accelerated charge transfer and increased active sites on their surfaces. In this work, CoS₂ nanoparticles decorated on MoS₂ nanorods are constructed and act as a superior cathode catalyst for Li-O₂ batteries. Coupling MoS₂ and CoS₂ can not only synergistically enhance their electrical conductivity and electrochemical activity, but also promote the heteroepitaxial growth of discharge products on the heterojunction interfaces, thus delivering high discharge capacity, stable cycle performance, and good rate capability.

Strategies toward anode stabilization in nonaqueous alkali metal-oxygen batteries

Alkali metal-O2 batteries exhibit ultra-high theoretical energy density which is even on a par with to fossil energy and expected to become the next generation of energy storage devices. However,...

Wax-Transferred Hydrophobic CVD Graphene Enables Water-Resistant and Dendrite-Free Lithium Anode toward Long Cycle Li-Air Battery

One of the key challenges in achieving practical lithium-air battery is the poor moisture tolerance of the lithium metal anode. Herein, guided by theoretical modeling, an effective tactic for realizing water-resistant Li anode by implementing a wax-assisted transfer protocol is reported to passivate the Li surface with an inert high-quality chemical vapor deposition (CVD) graphene layer. This electrically conductive and mechanically robust graphene coating enables serving as an artificial solid/electrolyte interphase (SEI), guiding homogeneous Li plating/stripping, suppressing dendrite and "dead" Li formation, as well as passivating the Li surface from moisture erosion and side reactions. Consequently, lithium-air batteries fabricated with the passivated Li anodes demonstrate a superb cycling performance up to 2300 h (230 cycles at 1000 mAh g-1 , 200 mA g-1 ). More strikingly, the anode recycled thereafter can be recoupled with a fresh cathode to continuously run for 400 extended hours. Comprehensive time-lapse and ex situ microscopic and spectroscopic investigations are further carried out for elucidating the fundamentals behind the extraordinary air and electrochemical stability.

Critical CO2 Concentration for Practical Lithium-Air Batteries

The Li-air battery is expected to become the next generation of the energy storage system because of its high theoretical energy density of 3500 Wh/kg (based on Li₂O₂ formation at the cathode). CO₂ (∼300 ppm) in the air is regarded as an impurity for cathode reactions, because it can lead to the formation of Li₂CO₃, which increases the overcharge potentials, decreases energy efficiency, and gives rise to the serious decomposition of battery components. However, the impact of a low concentration of CO₂ (<1000 ppm) on cell performance has not been addressed. In this work, we quantitatively characterized and analyzed the impact of a low concentration of CO₂ on the electrochemical performance of Li-air batteries to investigate the tolerance of Li-air batteries to CO₂. The discharge capacities and cyclability of the batteries with CO₂ below 100 ppm are similar to those without CO₂. The batteries with 0, 50, and 100 ppm of CO₂ delivered 85, 88, and 83 cycles, respectively. At the same time, the critical byproduct Li₂CO₃ was quantified, and its effect on batteries is analyzed by in situ electrochemical impedance spectroscopy (EIS) with a distribution of relaxation time (DRT) calculation. This study promises a theoretical basis for developing CO₂ removal materials and devices for Li-air batteries in the future.

Lithium-Air Batteries: Air-Breathing Challenges and Perspective

Lithium-oxygen (Li-O₂) batteries have been intensively investigated in recent decades for their utilization in electric vehicles. The intrinsic challenges arising from O₂ (electro)chemistry have been mitigated by developing various types of catalysts, porous electrode materials, and stable electrolyte solutions. At the next stage, we face the need to reform batteries by substituting pure O₂ gas with air from Earth's atmosphere. Thus, the key emerging challenges of Li-air batteries, which are related to the selective filtration of O₂ gas from air and the suppression of undesired reactions with other constituents in air, such as N₂, water vapor (H₂O), and carbon dioxide (CO₂), should be properly addressed. In this review, we discuss all key aspects for developing Li-air batteries that are optimized for operating in ambient air and highlight the crucial considerations and perspectives for future air-breathing batteries.

Two-Dimensional Transition Metal Chalcogenides for Alkali Metal Ions Storage

On the heels of exacerbating environmental concerns and ever-growing global energy demand, development of high-performance renewable energy-storage and -conversion devices has aroused great interest. The electrode materials, which are the critical components in electrochemical energy storage (EES) devices, largely determine the energy-storage properties, and the development of suitable active electrode materials is crucial to achieve efficient and environmentally friendly EES technologies albeit the challenges. Two-dimensional transition-metal chalcogenides (2D TMDs) are promising electrode materials in alkali metal ion batteries and supercapacitors because of ample interlayer space, large specific surface areas, fast ion-transfer kinetics, and large theoretical capacities achieved through intercalation and conversion reactions. However, they generally suffer from low electronic conductivities as well as substantial volume change and irreversible side reactions during the charge/discharge process, which result in poor cycling stability, poor rate performance, and low round-trip efficiency. In this Review, recent advances of 2D TMDs-based electrode materials for alkali metal-ion energy-storage devices with the focus on lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), high-energy lithium-sulfur (Li-S), and lithium-air (Li-O₂ ) batteries are described. The challenges and future directions of 2D TMDs-based electrode materials for high-performance LIBs, SIBs, PIBs, Li-S, and Li-O₂ batteries as well as emerging alkali metal-ion capacitors are also discussed.