Aprotic and aqueous Li-O₂ batteries

An efficient, bifunctional catalyst for lithium–oxygen batteries obtained through tuning the exterior Co2+/Co3+ ratio of CoOx on N-doped carbon nanofibers

CoO_x NPs@N-doped carbon nanofibers were obtained by an electrospinning technique and served as an excellent catalyst for Li–O₂ cells. The enhanced electrochemical performance can be ascribed to the rich Co²⁺ toward the ORR and OER on the surface of CoO_x.

Dendrite-free deposition on lithium anode toward long-life and high-stable Li//graphite dual-ion battery

Following modification with a carbon nanofibers film, an advanced Li//graphite dual-ion battery shows superior cycle life with dendrite-free Li anode.

Ru-Coated metal–organic framework-derived Co-based particles embedded in porous N-doped carbon nanocubes as a catalytic cathode for a Li–O2 battery

Ru-Co₄N/Co-NC is prepared and used as a cathode for a Li–O₂ battery, which shows high-capacity, low overpotential and long cycle-life.

Lithium–oxygen batteries with triplex Li+-selective solid membranes

A lithium–oxygen battery based on a Li⁺-selective solid membrane (LSSM) with a triplex (porous/dense/porous) structure is proposed.

A critical review of cathodes for rechargeable Mg batteries

Benefiting from a higher volumetric capacity (3833 mA h cm-3 for Mg vs. 2046 mA h cm-3 for Li) and dendrite-free Mg metal anode, reversible Mg batteries (RMBs) are a promising chemistry for applications beyond Li ion batteries. However, RMBs are still severely restricted by the absence of high performance cathodes for any practical application. In this review, we provide a critical and rigorous review of Mg battery cathode materials, mainly reported since 2013, focusing on the impact of structure and composition on magnesiation kinetics. We discuss cathode materials, including intercalation compounds, conversion materials (O2, S, organic compounds), water co-intercalation cathodes (V2O5, MnO2etc.), as well as hybrid systems using Mg metal anode. Among them, intercalation cathodes are further categorized by 3D (Chevrel phase, spinel structure etc.), 2D (layered structure), and 1D materials (polyanion: phosphate and silicate), according to the diffusion pathway of Mg2+ in the framework. Instead of discussing every published work in detail, this review selects the most representative works and highlights the merits and challenges of each class of cathodes. Advances in theoretical analysis are also reviewed and compared with experimental results. This critical review will provide comprehensive knowledge of Mg cathodes and guidelines for exploring new cathodes for rechargeable magnesium batteries.

Origin of the Overpotential for the Oxygen Evolution Reaction on a Well-Defined Graphene Electrode Probed by in Situ Sum Frequency Generation Vibrational Spectroscopy

To develop an efficient material for the cathode of the lithium-oxygen (Li-O₂) secondary battery, the oxygen reduction and evolution reactions (ORR and OER) on a well-defined graphene electrode have been investigated in a typical organic solvent, dimethyl sulfoxide (DMSO). The adsorption and desorption behaviors of the solvents on the graphene electrode surface were evaluated by an intrinsically surface-selective vibrational spectroscopy of sum frequency generation (SFG) during the ORR and OER. After the initial ORR depositing lithium peroxide (Li₂O₂) on the graphene electrode surface in a LiClO₄/DMSO solution, the SFG spectroscopy revealed that the subsequent OER oxidizing the Li₂O₂ preferentially proceeds at the interface between the Li₂O₂ and graphene rather than that between the Li₂O₂ and bulk solution. Therefore, the OER tends to reduce the electric conductivity between the Li₂O₂ and graphene by decreasing their contact area before a large part of the deposited Li₂O₂ was oxidized, which elucidates the origin of the high overpotential for the OER.

Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li-O2 Batteries

Ordered porous RuO₂ materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O₂ batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO₂ on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round-trip efficiency of Li-O₂ batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li⁺ and O₂ , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO₂ , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O₂ battery based on the RuO₂ cathode with an average pore size of 16 nm (RuO₂ -16) exhibits a high round-trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g^-1 with a voltage window of 2.5-4.0 V. The superior performance of RuO₂ -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO₂ can effectively reduce parasitic reactions compared with carbon materials.

Integration of Zn-Ag and Zn-Air Batteries: A Hybrid Battery with the Advantages of Both

We report a hybrid battery that integrates a Zn-Ag battery and a Zn-air battery to utilize the unique advantages of both battery systems. In the positive electrode, Ag nanoparticles couple the discharge behaviors through the two distinct electrochemical systems by working as the active reactant and the effective catalyst in the Zn-Ag and Zn-air reactions, respectively. In the negative electrode, in situ grown Zn particles provide large surface areas and suppress the dendrite, enabling the long-term operating safety. The battery first exhibits two-step voltage plateaus of 1.85 and 1.53 V in the Zn-Ag reaction, after which a voltage plateau of 1.25 V is delivered in the Zn-air reaction, and the specific capacity reaches 800 mAh g_Zn^-1. In addition, excellent reversibility and stability with maintaining high energy efficiency of 68% and a capacity retention of nearly 100% at 10 mA cm^-2 are demonstrated through 100 cycles, outperforming both conventional Zn-air and Zn-Ag batteries. This work brings forth a conceptually novel high-performance battery, and more generally opens up new vistas for developing hybrid electrochemical systems by integrating the advantages from two distinct ones.

Promoting Solution Discharge of Li-O2 Batteries with Immobilized Redox Mediators

For years, the aprotic Li-O₂ battery suffered from a severe capacity-current trade-off that would be unacceptable for a beyond Li-ion battery. Recent fundamental study of Li-O₂ electrochemistry revealed that this dilemma is caused by the growth of Li₂O₂ on the cathode surface and can be solved by discharging Li₂O₂ in the electrolyte solution. Among the strategies that can promote solution growth of Li₂O₂, redox mediators (i.e., soluble catalysts) demonstrate prominent performance. However, soluble redox mediators may shuttle from the cathode to the lithium anode and decompose thereon, causing severe deterioration of the lithium anode and degradation of the mediators' functionality. Here, we report that immobilized redox mediators (e.g., anthraquinone, AQ) in the form of a thin conductive polymer film (PAQ) on the cathode can effectively promote solution growth of Li₂O₂ even in weakly solvating electrolyte solutions that would otherwise lead to surface film growth and early cell death. The PAQ-catalyzed Li-O₂ battery can deliver a discharge capacity that is up to ∼50 times what its pristine counterpart does at the same current densities and is comparable to the capacity realized by soluble AQ-catalyzed Li-O₂ batteries. Most importantly, the adverse "cross-talk" between the lithium anode and the redox mediators immobilized on the cathode has been completely eliminated.

Water-Activated VOPO4 for Magnesium Ion Batteries

Rechargeable Mg batteries, using high capacity and dendrite-free Mg metal anodes, are promising energy storage devices for large scale smart grid due to low cost and high safety. However, the performance of Mg batteries is still plagued by the slow reaction kinetics of their cathode materials. Recent discoveries demonstrate that water in cathode can significantly enhance the Mg-ion diffusion in cathode by an unknown mechanism. Here, we propose the water-activated layered-structure VOPO₄ as a novel cathode material and examine the impact of water in electrode or organic electrolyte on the thermodynamics and kinetics of Mg-ion intercalation/deintercalation in cathodes. Electrochemical measurements verify that water in both VOPO₄ lattice and organic electrolyte can largely activate VOPO₄ cathode. Thermodynamic analysis demonstrates that the water in the electrolyte will equilibrate with the structural water in VOPO₄ lattice, and the water activity in the electrolyte alerts the mechanism and kinetics for electrochemical Mg-ion intercalation in VOPO₄. Theoretical calculations and experimental results demonstrate that water reduces both the solid-state diffusion barrier in the VOPO₄ electrode and the desolvation penalty at the interface. To achieve fast reaction kinetics, the water activity in the electrolyte should be larger than 10^-2. The proposed activation mechanism provides guidance for screening and designing novel chemistry for high performance multivalent-ion batteries.

Synthesis and Progress of New Oxygen-Vacant Electrode Materials for High-Energy Rechargeable Battery Applications

During the last few years, a great amount of oxygen-vacant materials have been synthetized and applied as electrodes for electrochemical storage. The presence of oxygen vacancies leads to an increase in the conductivity and the diffusion coefficient; consequently, the controllable synthesis of oxygen vacancy plays an important role in improving the electrochemical performance, including achieving high specific capacitance, high power density, high energy density, and good cycling stability of the electrode materials for batteries. This review mainly focuses on research progress in the preparation of oxygen-vacant nanostructures and the application of materials with oxygen vacancies in various batteries (such as lithium-ion, lithium-oxygen, and sodium-ion batteries). Challenges related to and opportunities for oxygen-vacant materials are also provided.

Ultrahigh-Capacity and Long-Life Lithium-Metal Batteries Enabled by Engineering Carbon Nanofiber-Stabilized Graphene Aerogel Film Host

A safe, high-capacity, and long-life Li metal anode is highly desired due to recent developments in high-energy-density Li-metal batteries. However, there are still rigorous challenges associated with the undesirable formation of Li dendrites, lack of suitable host materials, and unstable chemical interfaces. Herein, a carbon nanofiber-stabilized graphene aerogel film (G-CNF film), inspired by constructional engineering, is constructed. As the host material for Li deposition, the G-CNF film features a large surface area, porous structure, and a robust skeleton that can render low local current density. This allows for dendrite-free Li deposition and mitigation of problems associated with large volume change. Importantly, the G-CNF film can keep high Li plating/stripping efficiency at nearly 99% for over 700 h with an areal capacity of 10 mA h cm^-2 (the specific capacity up to 2588 mA h g^-1 based on the total mass of carbon host and Li metal). The symmetric cells can stably run for more than 1000 h with low voltage hysteresis. The full cell with the LiFePO₄ cathode also delivers enhanced capacity and lowered overpotential. As two-in-one host materials for both cathodes and anodes in Li-O₂ batteries, the battery exhibits a capacity of 1.2 mA h cm^-2 .

Dendrite-Free Epitaxial Growth of Lithium Metal during Charging in Li-O2 Batteries

Lithium (Li) dendrite formation is one of the major hurdles limiting the development of Li-metal batteries, including Li-O₂ batteries. Herein, we report the first observation of the dendrite-free epitaxial growth of a Li metal up to 10-μm thick during charging (plating) in the LiBr-LiNO₃ dual anion electrolyte under O₂ atmosphere. This phenomenon is due to the formation of an ultrathin and homogeneous Li₂ O-rich solid-electrolyte interphase (SEI) layer in the preceding discharge (stripping) process, where the corrosive nature of Br^- seems to give rise to remove the original incompact passivation layer and NO₃^- oxidizes (passivates) the freshly formed Li surface to prevent further reactions with the electrolyte. Such reactions keep the SEI thin (<100 nm) and facilitates the electropolishing effect and gets ready for the epitaxial electroplating of Li in the following charge process.

Electrochemical Conversion of Nitrogen Trifluoride as a Gas-to-Solid Cathode in Li Batteries

Nonaqueous metal-gas batteries have emerged as a growing family of primary and rechargeable batteries with high capacities and energy densities. We herein report a high-capacity primary Li-gas battery that uses a perfluorinated gas, nitrogen trifluoride (NF₃), as the cathode reactant. Gravimetric capacities of ∼1100 and 4000 mAh/g_C are achieved at 25 and 55 °C, respectively (at 20 mA/g_C), with discharge voltages up to 2.6 V vs Li/Li⁺. NF₃ reduction occurs by a 3e^-/NF₃ process, yielding polycrystalline lithium fluoride (LiF) on a carbon cathode. The detailed electrochemical NF₃ conversion mechanism is proposed and supported by solid- and liquid-phase characterization and theoretical computation, revealing the origin of observed discharge overpotentials and elucidating the significant contribution of N-F bond cleavage. These findings indicate the value of exploring fluorinated gas cathodes for primary batteries; moreover, they open new avenues for future targeted electrocatalyst design and cathode materials synthesis applications benefiting from conformal coatings of LiF.

Performance-improved Li-O2 batteries by tailoring the phases of MoxC porous nanorods as an efficient cathode

Novel nitrogen-doped porous molybdenum carbide (α-MoC1-x and β-Mo2C) architectures were prepared using Mo-based metal-organic frameworks (MOFs) as the precursor. The synthesized molybdenum carbides consist of numerous nanocrystals organized into micro-sized rods with interpenetrating mesoporous-channels and macroporous-tunnels along the axial direction. When employed as the cathode catalyst for Li-O2 batteries, this dual pore configuration offers abundant active sites for the electrochemical reaction and many nucleation sites for the discharge product of Li2O2; hence, decent performances were obtained. Among the two synthesized molybdenum carbides, the α-MoC1-x electrode stands out as being better due to its lower charge transfer resistance (395.8 Ω compared to 627.9 Ω) and better O2 adsorption (binding energy of -1.87 eV of α-(111)-Mo compared to -0.72 eV of β-(101)-Mo). It delivered a high full discharge of 20 212 mA h g-1 with a discharge voltage of 2.62 V at 200 mA g-1. A good cycling stability was also obtained: i.e. 100 stable cycles with a fixed capacity of 1000 mA h g-1 (at a current density of 200 mA g-1) with a charging voltage of 4.24 V and maintaining a respectable round-trip efficiency of ∼70%.

Lithium metal stripping beneath the solid electrolyte interphase

Lithium stripping is a crucial process coupled with lithium deposition during the cycling of Li metal batteries. Lithium deposition has been widely studied, whereas stripping as a subsurface process has rarely been investigated. Here we reveal the fundamental mechanism of stripping on lithium by visualizing the interface between stripped lithium and the solid electrolyte interphase (SEI). We observed nanovoids formed between lithium and the SEI layer after stripping, which are attributed to the accumulation of lithium metal vacancies. High-rate dissolution of lithium causes vigorous growth and subsequent aggregation of voids, followed by the collapse of the SEI layer, i.e., pitting. We systematically measured the lithium polarization behavior during stripping and find that the lithium cation diffusion through the SEI layer is the rate-determining step. Nonuniform sites on typical lithium surfaces, such as grain boundaries and slip lines, greatly accelerated the local dissolution of lithium. The deeper understanding of this buried interface stripping process provides beneficial clues for future lithium anode and electrolyte design.

Graphene Oxide Sieving Membrane for Improved Cycle Life in High-Efficiency Redox-Mediated Li-O2 batteries

As soluble catalysts, redox-mediators (RMs) endow mobility to catalysts for unconstrained access to tethered solid discharge products, lowering the energy barrier for Li₂ O₂ formation/decomposition; however, this desired mobility is accompanied by the undesirable side effect of RM migration to the Li metal anode. The reaction between RMs and Li metal degrades both the Li metal and the RMs, leading to cell deterioration within a few cycles. To extend the cycle life of redox-mediated Li-O₂ batteries, herein graphene oxide (GO) membranes are reported as RM-blocking separators. It is revealed that the size of GO nanochannels is narrow enough to reject 5,10-dihydro-5,10-dimethylphenazine (DMPZ) while selectively allowing the transport of smaller Li⁺ ions. The negative surface charges of GO further repel negative ions via Donnan exclusion, greatly improving the lithium ion transference number. The Li-O₂ cells with GO membranes efficiently harness the redox-mediation activity of DMPZ for improved performance, achieving energy efficiency of above 80% for more than 25 cycles, and 90% for 78 cycles when the capacity limits were 0.75 and 0.5 mAh cm^-2 , respectively. Considering the facile preparation of GO membranes, RM-sieving GO membranes can be cost-effective and processable functional separators in Li-O₂ batteries.

Flexible, Flame-Resistant, and Dendrite-Impermeable Gel-Polymer Electrolyte for Li-O2 /Air Batteries Workable Under Hurdle Conditions

Gel-polymer electrolytes are considered as a promising candidate for replacing the liquid electrolytes to address the safety concerns in Li-O₂ /air batteries. In this work, by taking advantage of the hydrogen bond between thermoplastic polyurethane and aerogel SiO₂ in gel polymer, a highly crosslinked quasi-solid electrolyte (FST-GPE) with multifeatures of high ionic conductivity, high mechanical flexibility, favorable flame resistance, and excellent Li dendrite impermeability is developed. The resulting gel-polymer Li-O₂ /air batteries possess high reaction kinetics and stabilities due to the unique electrode-electrolyte interface and fast O₂ diffusion in cathode, which can achieve up to 250 discharge-charge cycles (over 1000 h) in oxygen gas. Under ambient air atmosphere, excellent performances are observed for coin-type cells over 20 days and for prototype cells working under extreme bending conditions. Moreover, the FST-GPE electrolyte also exhibits durability to protect against fire, dendritic Li, and H₂ O attack, demonstrating great potential for the design of practical Li-O₂ /air batteries.

A lithium ion/oxygen hybrid battery with high energy and high power

A novel lithium ion/oxygen hybrid battery system is proposed that uses the advantages and minimizes the disadvantages of both lithium-ion batteries (LIBs) and lithium-oxygen batteries (LOBs). In it, the LOB-part plays range-extending and high-power output roles, while using the discharge-priority of the LIB-part is suggested to compensate the cycling-life shortcomings of the LOB-part.

Improved structural design of single- and double-wall MnCo2O4 nanotube cathodes for long-life Li-O2 batteries

Developing a cathode material with a stable pore structure and efficient bifunctional activity toward oxygen electrochemistry is the key to achieve practical and high-performance Li-O2 batteries. Here, hierarchically porous MnCo2O4 nanotubes with single- or double-wall architecture are fabricated through a facile electrospinning technique, by adjusting the concentration of the electrospinning solution. The electrochemical measurements indicate that both types of nanotubes possess excellent catalytic abilities toward oxygen reduction and evolution reactions in alkaline aqueous or non-aqueous media. When used as air-electrode catalysts for Li-O2 batteries, both single- and double-wall MnCo2O4 nanotubes show significantly improved electrochemical performance. In particular, the novel double-wall MnCo2O4 nanotubes (DW-MCO-NT), with a high surface area and a large pore volume almost twice as big as the single-wall nanotubes, can offer numerous catalytically active sites as well as sufficient space to deposit discharge products. The DW-MCO-NT based Li-O2 batteries can deliver a maximum discharge capacity of 8100 mA h g-1, with a potential plateau at 2.77 V, and achieve an excellent cyclability over 278 cycles, under strict conditions of 1000 mA h g-1 at 400 mA g-1 within 2.6-4.3 V. Moreover, the XRD and SEM analyses show that the dominant discharge product with a particulate shape is crystal Li2O2 and is prone to being completely decomposed, endowing the MnCo2O4 nanotube-based Li-O2 battery with a long cycle life.

Engineering stable interfaces for three-dimensional lithium metal anodes

Lithium metal has long been considered one of the most promising anode materials for advanced lithium batteries (for example, Li-S and Li-O₂), which could offer significantly improved energy density compared to state-of-the-art lithium ion batteries. Despite decades of intense research efforts, its commercialization remains limited by poor cyclability and safety concerns of lithium metal anodes. One root cause is the parasitic reaction between metallic lithium and the organic liquid electrolyte, resulting in continuous formation of an unstable solid electrolyte interphase, which consumes both active lithium and electrolyte. Until now, it has been challenging to completely shut down the parasitic reaction. We find that a thin-layer coating applied through atomic layer deposition on a hollow carbon host guides lithium deposition inside the hollow carbon sphere and simultaneously prevents electrolyte infiltration by sealing pinholes on the shell of the hollow carbon sphere. By encapsulating lithium inside the stable host, parasitic reactions are prevented, resulting in impressive cycling behavior. We report more than 500 cycles at a high coulombic efficiency of 99% in an ether-based electrolyte at a cycling rate of 0.5 mA/cm² and a cycling capacity of 1 mAh/cm², which is among the most stable Li anodes reported so far.

Unveiling the Complex Effects of H2O on Discharge-Recharge Behaviors of Aprotic Lithium-O2 Batteries

The addition of H₂O, even trace amount, in aprotic Li-O₂ batteries has a remarkable impact on achieving high capacity by triggering solution mechanism, and even reducing charge overpotential. However, the critical role of H₂O in promoting solution mechanism still lacks persuasive spectroscopic evidence, moreover, the origin of low polarization remains incompletely understood. Herein, by in situ spectroscopic identification of reaction intermediates, we directly verify that H₂O additive is able to alter oxygen reduction reaction (ORR) pathway subjected to solution-mediated growth mechanism of Li₂O₂. In addition, ingress of H₂O also induces to form partial LiOH, resulting in reduced charging polarization due to its higher conductivity; however, LiOH could not contribute to O₂ evolution upon recharge. These original results unveil the complex effects of H₂O on cycling the aprotic Li-O₂ batteries, which are instructive for the mechanism study of aprotic Li-O₂ batteries with protic additives or soluble catalysts.

In Situ Imaging the Oxygen Reduction Reactions of Solid State Na-O2 Batteries with CuO Nanowires as the Air Cathode

We report real time imaging of the oxygen reduction reactions (ORRs) in all solid state sodium oxygen batteries (SOBs) with CuO nanowires (NWs) as the air cathode in an aberration-corrected environmental transmission electron microscope under an oxygen environment. The ORR occurred in a distinct two-step reaction, namely, a first conversion reaction followed by a second multiple ORR. In the former, CuO was first converted to Cu₂O and then to Cu; in the latter, NaO₂ formed first, followed by its disproportionation to Na₂O₂ and O₂. Concurrent with the two distinct electrochemical reactions, the CuO NWs experienced multiple consecutive large volume expansions. It is evident that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter one-electron-transfer ORR, leading to the formation of NaO₂. Remarkably, no carbonate formation was detected in the oxygen cathode after cycling due to the absence of carbon source in the whole battery setup. These results provide fundamental understanding into the oxygen chemistry in the carbonless air cathode in all solid state Na-O₂ batteries.

Two-Dimensional Phosphorene-Derived Protective Layers on a Lithium Metal Anode for Lithium-Oxygen Batteries

Lithium-oxygen (Li-O₂) batteries are desirable for electric vehicles because of their high energy density. Li dendrite growth and severe electrolyte decomposition on Li metal are, however, challenging issues for the practical application of these batteries. In this connection, an electrochemically active two-dimensional phosphorene-derived lithium phosphide is introduced as a Li metal protective layer, where the nanosized protective layer on Li metal suppresses electrolyte decomposition and Li dendrite growth. This suppression is attributed to thermodynamic properties of the electrochemically active lithium phosphide protective layer. The electrolyte decomposition is suppressed on the protective layer because the redox potential of lithium phosphide layer is higher than that of electrolyte decomposition. Li plating is thermodynamically unfavorable on lithium phosphide layers, which hinders Li dendrite growth during cycling. As a result, the nanosized lithium phosphide protective layer improves the cycle performance of Li symmetric cells and Li-O₂ batteries with various electrolytes including lithium bis(trifluoromethanesulfonyl)imide in N,N-dimethylacetamide. A variety of ex situ analyses and theoretical calculations support these behaviors of the phosphorene-derived lithium phosphide protective layer.

Free-Standing Air Cathodes Based on 3D Hierarchically Porous Carbon Membranes: Kinetic Overpotential of Continuous Macropores in Li-O2 Batteries

Free-standing macroporous air electrodes with enhanced interfacial contact, rapid mass transport, and tailored deposition space for large amounts of Li₂ O₂ are essential for improving the rate performance of Li-O₂ batteries. An ordered mesoporous carbon membrane with continuous macroporous channels was prepared by inversely topological transformation from ZnO nanorod array. Utilized as a free-standing air cathode for Li-O₂ battery, the hierarchically porous carbon membrane shows superior rate performance. However, the increased cross-sectional area of the continuous macropores on the cathode surface leads to a kinetic overpotential with large voltage hysteresis and linear voltage variation against Butler-Volmer behavior. The kinetics were investigated based on the rate-determining step of second electron transfer accompanied by migration of Li⁺ in solid or quasi-solid intermediates. These discoveries shed light on the design of the air cathode for Li-O₂ batteries with high-rate performance.

Strongly Coupled Carbon Nanosheets/Molybdenum Carbide Nanocluster Hollow Nanospheres for High-Performance Aprotic Li-O2 Battery

A highly efficient oxygen electrode is indispensable for achieving high-performance aprotic lithium-O₂ batteries. Herein, it is demonstrated that strongly coupled carbon nanosheets/molybdenum carbide (α-MoC_1-x ) nanocluster hierarchical hybrid hollow spheres (denoted as MoC_1-x /HSC) can work well as cathode for boosting the performance of lithium-O₂ batteries. The important feature of MoC_1-x /HSC is that the α-MoC_1-x nanoclusters, uniformly incorporated into carbon nanosheets, can not only effectively prevent the nanoclusters from agglomeration, but also help enhance the interaction between the nanoclusters and the conductive substrate during the charge and discharge process. As a consequence, the MoC_1-x /HSC shows significantly improved electrocatalytic performance in an aprotic Li-O₂ battery with greatly reduced charge and discharge overpotentials and long cycle stability. The ex situ scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy studies reveal that the mechanism for the high-performance Li-O₂ battery using MoC_1-x /HSC as cathode is that the incorporated molybdenum carbide nanoclusters can make oxygen reduction on their surfaces easy, and finally form amorphous film-like Li-deficient Li₂ O₂ with the ability to decompose at a low potential. To the best of knowledge, the MoC_1-x /HSC of this paper is among the best cathode materials for lithium-O₂ batteries reported to date.

Advanced Architectures and Relatives of Air Electrodes in Zn-Air Batteries

Zn-air batteries are becoming the promising power sources for portable and wearable electronic devices and hybrid/electric vehicles because of their high specific energy density and the low cost for next-generation green and sustainable energy technologies. An air electrode integrated with an oxygen electrocatalyst is the most important component and inevitably determines the performance and cost of a Zn-air battery. This article presents exciting advances and challenges related to air electrodes and their relatives. After a brief introduction of the Zn-air battery, the architectures and oxygen electrocatalysts of air electrodes and relevant electrolytes are highlighted in primary and rechargeable types with different configurations, respectively. Moreover, the individual components and major issues of flexible Zn-air batteries are also highlighted, along with the strategies to enhance the battery performance. Finally, a perspective for design, preparation, and assembly of air electrodes is proposed for the future innovations of Zn-air batteries with high performance.

A methyl pivalate based electrolyte for non-aqueous lithium-oxygen batteries

A methyl pivalate (MP) based electrolyte was for the first time reported for non-aqueous lithium-oxygen (Li-O₂) batteries. This new electrolyte in both superoxide radical solution and a real Li-O₂ battery environment showed good chemical stability against superoxide radicals, which was confirmed by ¹H NMR and ¹³C NMR measurements.