A High‐Performance Li–O2 Battery with a Strongly Solvating Hexamethylphosphoramide Electrolyte and a LiPON‐Protected Lithium Anode

The aprotic Li–O₂ battery has attracted a great deal of interest because theoretically it can store more energy than today's Li‐ion batteries. However, current Li–O₂ batteries suffer from passivation/clogging of the cathode by discharged Li₂O₂, high charging voltage for its subsequent oxidation, and accumulation of side reaction products (particularly Li₂CO₃ and LiOH) upon cycling. Here, an advanced Li–O₂ battery with a hexamethylphosphoramide (HMPA) electrolyte is reported that can dissolve Li₂O₂, Li₂CO₃, and LiOH up to 0.35, 0.36, and 1.11 × 10^?3m , respectively, and a LiPON‐protected lithium anode that can be reversibly cycled in the HMPA electrolyte. Compared to the benchmark of ether‐based Li–O₂ batteries, improved capacity, rate capability, voltaic efficiency, and cycle life are achieved for the HMPA‐based Li–O₂ cells. More importantly, a combination of advanced research techniques provide compelling evidence that operation of the HMPA‐based Li–O₂ battery is backed by nearly reversible formation/decomposition of Li₂O₂ with negligible side reactions.     

The Salt Matters: Enhanced Reversibility of Li–O2 Batteries with a Li[(CF3SO2)(n‐C4F9SO2)N]‐Based Electrolyte

The safety hazards and cycle instability of lithium metal anodes (LMA) constitute significant barriers to progress in lithium metal batteries. This situation is worse in Li–O₂ batteries because the LMA is prone to be chemically attacked by O₂ shuttled from the cathode. Notwithstanding, efforts on LMA are much sparse than those on the cathode in the realm of Li–O₂ batteries. Here, a novel lithium salt of Li[(CF₃SO₂)(n‐C₄F₉SO₂)N] (LiTNFSI) is reported, which can effectively suppress the parasitic side reactions and dendrite growth of LMA during cycling and thereby significantly enhance the overall reversibility of Li–O₂ batteries. A variety of advanced research tools are employed to scrutinize the working principles of the LiTNFSI salt. It is revealed that a stable, uniform, and O₂‐resistive solid electrolyte interphase is formed on LMA, and hence the “cross‐talk” between the LMA and O₂ shuttled from the cathode is remarkably inhibited in LiTNFSI‐based Li–O₂ batteries.     

High‐Capacity and High‐Rate Discharging of a Coenzyme Q10‐Catalyzed Li–O2 Battery

Discharging of the aprotic Li–O₂ battery relies on O₂ reduction to insulating solid Li₂O₂, which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li–O₂ batteries with high capacity and high rate capability, it is crucially important to discharge Li₂O₂ in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q₁₀ (CoQ₁₀) that can efficaciously drive solution phase formation of Li₂O₂ in current benchmark ether‐based Li–O₂ batteries is reported, which would otherwise lead to Li₂O₂ surface‐film growth and premature cell death. In the range of current densities of 0.1–0.5 mA cm^?2_areal, the CoQ₁₀‐catalyzed Li–O₂ battery can deliver a discharge capacity that is ≈40–100 times what the pristine Li–O₂ battery could achieve. The drastically enhanced electrochemical performance is attributed to the CoQ₁₀ that not only efficiently mediates the electron transfer from the cathode to dissolve O₂ but also strongly interacts with the newly formed Li₂O₂ in solution retarding its precipitation on the cathode surface. The mediated oxygen reduction reaction and the bonding mechanism between CoQ₁₀ and Li₂O₂ are understood with density functional theory calculations.     

Direct Visualization of the Reversible O2−/O− Redox Process in Li‐Rich Cathode Materials

Conventional cathodes of Li‐ion batteries mainly operate through an insertion–extraction process involving transition metal redox. These cathodes will not be able to meet the increasing requirements until lithium‐rich layered oxides emerge with beyond‐capacity performance. Nevertheless, in‐depth understanding of the evolution of crystal and excess capacity delivered by Li‐rich layered oxides is insufficient. Herein, various in situ technologies such as X‐ray diffraction and Raman spectroscopy are employed for a typical material Li_1.2Ni_0.2Mn_0.6O₂, directly visualizing O^?? O^? (peroxo oxygen dimers) bonding mostly along the c‐axis and demonstrating the reversible O^2?/O^? redox process. Additionally, the formation of the peroxo O? O bond is calculated via density functional theory, and the corresponding O? O bond length of ≈1.3 Å matches well with the in situ Raman results. These findings enrich the oxygen chemistry in layered oxides and open opportunities to design high‐performance positive electrodes for lithium‐ion batteries.     

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 Li₂O₂ 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.     

Zero Linear Compressibility in Nondense Borates with a “Lu‐Ban Stool”‐Like Structure

Discovering materials that exhibit zero linear compressibility (ZLC) behavior under hydrostatic pressure is extremely difficult. To date, only a handful of ZLC materials have been found, and almost all of them are ultrahard materials with densified structures. Here, to explore ZLC in nondense materials, a structural model analogous to the structure of the “Lu‐Ban stool,” a product of traditional Chinese woodworking invented 2500 years ago, is proposed. The application of this model to borates leads to the discovery of ZLC in AEB₂O₄ (AE = Ca and Sr) with the unique “Lu‐Ban stool”‐like structure, which can obtain a subtle mechanical balance between pressure‐induced expansion and contraction effects. Coupled with the very wide ultraviolet transparent windows, the ZLC behavior of AEB₂O₄ may result in some unique but important applications. The applications of the “Lu‐Ban stool” model open a new route for pursuing ZLC materials in nondense structural systems.     

A Novel Organic “Polyurea” Thin Film for Ultralong‐Life Lithium‐Metal Anodes via Molecular‐Layer Deposition

Metallic Li is considered as one of the most promising anode materials for next‐generation batteries due to its high theoretical capacity and low electrochemical potential. However, its commercialization has been impeded by the severe safety issues associated with Li‐dendrite growth. Non‐uniform Li‐ion flux on the Li‐metal surface and the formation of unstable solid electrolyte interphase (SEI) during the Li plating/stripping process lead to the growth of dendritic and mossy Li structures that deteriorate the cycling performance and can cause short‐circuits. Herein, an ultrathin polymer film of “polyurea” as an artificial SEI layer for Li‐metal anodes via molecular‐layer deposition (MLD) is reported. Abundant polar groups in polyurea can redistribute the Li‐ion flux and lead to a uniform plating/stripping process. As a result, the dendritic Li growth during cycling is efficiently suppressed and the life span is significantly prolonged (three times longer than bare Li at a current density of 3 mA cm^?2). Moreover, the detailed surface and interfacial chemistry of Li metal are studied comprehensively. This work provides deep insights into the design of artificial SEI coatings for Li metal and progress toward realizing next‐generation Li‐metal batteries.     

Superior Potassium Ion Storage via Vertical MoS2 “Nano‐Rose” with Expanded Interlayers on Graphene

Potassium has its unique advantages over lithium or sodium as a charge carrier in rechargeable batteries. However, progresses in K‐ion battery (KIB) chemistry have so far been hindered by lacking suitable electrode materials to host the relatively large K⁺ ions compared to its Li⁺ and Na⁺ counterparts. Herein, molybdenum disulfide (MoS₂) “roses” grown on reduced graphene oxide sheets (MoS₂@rGO) are synthesized via a two‐step solvothermal route. The as‐synthesized MoS₂@rGO composite, with expanded interlayer spacing of MoS₂, chemically bonded between MoS₂ and rGO, and a unique nano‐architecture, displays the one of the best electrochemical performances to date as an anode material for nonaqueous KIBs. More importantly, a combined K⁺ storage mechanism of intercalation and conversion reaction is also revealed. The findings presented indicate the enormous potential of layered metal dichalcogenides as advanced electrode materials for high‐performance KIBs and also provide new insights and understanding of K⁺ storage mechanism.     

Designing a Multifunctional Separator for High‐Performance Li–S Batteries at Elevated Temperature

The practical applications of lithium–sulfur (Li–S) batteries are seriously limited by the undesirable polysulfide shuttling and lithium dendrite growth. Herein, a multifunctional membrane is designed and prepared by coating a lithiated Nafion (Li@Nafion) layer and an Al₂O₃ layer on the two sides of a routine polymer membrane (polypropylene/polyethylene/polypropylene, PEP). The Li@Nafion layer faced to the sulfur cathode builds a “polysulfide‐phobic” surface to restrain the shuttle effect via Coulomb repulsion, while the Al₂O₃ layer with a uniform porous structure aids in regulating homogeneous Li⁺ fluxes to achieve stable Li electrodeposition. As a result, the Li//Li symmetric cell with a Li@Nafion/PEP/Al₂O₃ (LNPA) separator realizes stable Li plating/striping even after 1000 h at a high current density (5 mA cm^?2). Moreover, the Li–S batteries incorporating LNPA separators not only can achieve excellent outstanding cyclic stability at an ultrahigh sulfur loading (7.6 mg cm^?2), but also exhibit impressive electrochemical performance at an elevated temperature (60 °C). The rational design of the LNPA separator presents new insights to develop high‐performance Li–S batteries.     

A High‐Capacity O2‐Type Li‐Rich Cathode Material with a Single‐Layer Li2MnO3 Superstructure

A high capacity cathode is the key to the realization of high‐energy‐density lithium‐ion batteries. The anionic oxygen redox induced by activation of the Li₂MnO₃ domain has previously afforded an O3‐type layered Li‐rich material used as the cathode for lithium‐ion batteries with a notably high capacity of 250–300 mAh g^?1. However, its practical application in lithium‐ion batteries has been limited due to electrodes made from this material suffering severe voltage fading and capacity decay during cycling. Here, it is shown that an O2‐type Li‐rich material with a single‐layer Li₂MnO₃ superstructure can deliver an extraordinary reversible capacity of 400 mAh g^?1 (energy density: ≈1360 Wh kg^?1). The activation of a single‐layer Li₂MnO₃ enables stable anionic oxygen redox reactions and leads to a highly reversible charge–discharge cycle. Understanding the high performance will further the development of high‐capacity cathode materials that utilize anionic oxygen redox processes.     

Absorption Enhancement in “Giant” Core/Alloyed‐Shell Quantum Dots for Luminescent Solar Concentrator

Luminescent solar concentrators (LSCs) can potentially reduce the cost of solar cells by decreasing the photoactive area of the device and boosting the photoconversion efficiency (PCE). This study demonstrates the application of “giant” CdSe/Cd_xPb_1–xS core/shell quantum dots (QDs) as light harvesters in high performance LSCs with over 1.15% PCE. Pb addition is critical to maximize PCE. First, this study synthesizes “giant” CdSe/Cd_xPb_1–xS QDs with high quantum yield (40%), narrow size distribution (<10%), and stable photoluminescence in a wide temperature range (100–300 K). Subsequently these thick alloyed‐shell QDs are embedded in a polymer matrix, resulting in a highly transparent composite with absorption spectrum covering the range 300–600 nm, and are applied as active material for prototype LSCs. The latter exhibits a 15% enhancement in efficiency with respect to 1% PCE of the pure‐CdS‐shelled QDs. This study attributes this increase to the contribution of Pb doping. The results demonstrate a straightforward approach to enhance light absorption in “giant” QDs by metal doping, indicating a promising route to broaden the absorption spectrum and increase the efficiency of LSCs.     

Effect of hinokitiol impregnated sheets on shelf life and quality of “KEK‐1” tomatoes during storage

Hinokitiol (β‐thujaplicin, volatile oil extracted from the wood of Hiba arborvitae [Thujopsis dolabrata var. hondae], cypress family) is a natural preservative, antimicrobial, and chelating agent, used to prevent decay and extend the shelf life of fruits and vegetables. In the present study, we used nonwoven rayon sheets impregnated with hinokitiol to conduct packaging studies. Mature green tomatoes var. “KEK‐1” were packaged under three packaging conditions, ie, modified atmosphere packaging (MAP), MAP + hinokitiol (MH), and perforated film package (as control), and their quality attributes were compared during storage. The packaging materials used were low‐density polyethylene (LDPE) film (40 μm) and fresh sheets of nonwoven rayon impregnated with hinokitiol. O₂ in the MAP packaged tomatoes were retained throughout the storage period (3% to 5% O₂). Results showed that MH had slightly improved quality attributes throughout the storage period when compared with MAP alone. Expression levels of LeACS, LeADH, and LeTBG4 genes were higher in 5 and 9 days of control when compared with MAP and MH. “KEK‐1” tomatoes had longer shelf life under MAP and MH packaging and maintained the quality at 15°C. Hence, the effect of the MAP with bioactive packaging treatments could be effective in the future application for the extension of shelf life and quality of fruits and vegetables.     

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 H₂O attack, demonstrating great potential for the design of practical Li–O₂/air batteries.     

Oxidized Laser‐Induced Graphene for Efficient Oxygen Electrocatalysis

An efficient metal‐free catalyst is presented for oxygen evolution and reduction based on oxidized laser‐induced graphene (LIG‐O). The oxidation of LIG by O₂ plasma to form LIG‐O boosts its performance in the oxygen evolution reaction (OER), exhibiting a low onset potential of 260 mV with a low Tafel slope of 49 mV dec^?1, as well as an increased activity for the oxygen reduction reaction. Additionally, LIG‐O shows unexpectedly high activity in catalyzing Li₂O₂ decomposition in Li‐O₂ batteries. The overpotential upon charging is decreased from 1.01 V in LIG to 0.63 V in LIG‐O. The oxygen‐containing groups make essential contributions, not only by providing the active sites, but also by facilitating the adsorption of OER intermediates and lowering the activation energy.     

Redox Mediators for Li–O2 Batteries: Status and Perspectives

Li–O₂ batteries have received much attention due to their extremely large theoretical energy density. However, the high overpotentials required for charging Li–O₂ batteries lower their energy efficiency and degrade the electrolytes and carbon electrodes. This problem is one of the main obstacles in developing practical Li–O₂ batteries. To solve this problem, it is important to facilitate the oxidation of Li₂O₂ upon charging by using effective electrocatalysis. Using solid catalysts is not too effective for oxidizing the electronically isolating Li‐peroxide layers. In turn, for soluble catalysts, red‐ox mediators (RMs) are homogeneously dissolved in the electrolyte solutions and can effectively oxidize all of the Li₂O₂ precipitated during discharge. RMs can decompose solid Li₂O₂ species no matter their size, morphology, or thickness and thus dramatically increase energy efficiency. However, some negative side effects, such as the shuttle reactions of RMs and deterioration of the Li‐metal occur. Therefore, it is necessary to study the activity and stability of RMs in Li–O₂ batteries in detail. Herein, recent studies related to redox mediators are reviewed and the mechanisms of redox reactions are illustrated. The development opportunities of RMs for this important battery technology are discussed and future directions are suggested.     

Water-Trapping Single-Atom Co-N4/Graphene Triggering Direct 4e− LiOH Chemistry for Rechargeable Aprotic Li–O2 Batteries

Lithium–oxygen (Li–O₂) batteries have received extensive attention owing to ultrahigh theoretical energy density. Compared to typical discharge product Li₂O₂, LiOH has attracted much attention for its better chemical and electrochemical stability. Large-scale applications of Li–O₂ batteries with LiOH chemistry are hampered by the serious internal shuttling of the water additives with the desired 4e⁻ electrochemical reactions. Here, a metal organic framework-derived “water-trapping” single-atom-Co-N₄/graphene catalyst (Co-SA-rGO) is provided that successfully mitigates the water shuttling and enables the direct 4e⁻ catalytic reaction of LiOH in the aprotic Li–O₂ battery. The Co-N₄ center is more active toward proton-coupled electron transfer, benefiting - direction 4e⁻ formation of LiOH. 3D interlinked networks also provide large surface area and mesoporous structures to trap ≈12 wt% H₂O molecules and offer rapid tunnels for O₂ diffusion and Li⁺ transportation. With these unique features, the Co-SA-rGO based Li–O₂ battery delivers a high discharge platform of 2.83 V and a large discharge capacity of 12 760.8 mAh g⁻¹. Also, the battery can withstand corrosion in the air and maintain a stable discharge platform for 220 cycles. This work points out the direction of enhanced electron/proton transfer for the single-atom catalyst design in Li–O₂ batteries.     

Grain‐Boundary “Patches” by In Situ Conversion to Enhance Perovskite Solar Cells Stability

The power conversion efficiency of organic–inorganic hybrid perovskite solar cells has increased rapidly, but the device stability remains a big challenge. Previous studies show the grain boundary (GB) can facilitate ion migration and initiate device degradation. Herein, methimazole (MMI) is employed for the first time to construct a surface “patch” by in situ converting residual PbI₂ at GBs. The resultant MMI–PbI₂ complex can effectively suppress ion migration and inhibit diffusion of the metal electrodes. The origin of the surface “patch” effect and their working mechanisms are investigated experimentally and theoretically at the microscopic level. It hence demonstrates a simple and effective method to prolong the device stability in the context of GB engineering, which could be extensively applied to perovskite‐based optoelectronics.     

In Situ Construction of Stable Tissue‐Directed/Reinforced Bifunctional Separator/Protection Film on Lithium Anode for Lithium–Oxygen Batteries

To achieve a high reversibility and long cycle life for Li–O₂ battery system, the stable tissue‐directed/reinforced bifunctional separator/protection film (TBF) is in situ fabricated on the surface of metallic lithium anode. It is shown that a Li–O₂ cell composed of the TBF‐modified lithium anodes exhibits an excellent anodic reversibility (300 cycles) and effectively improved cathodic long lifetime (106 cycles). The improvement is attributed to the ability of the TBF, which has chemical, electrochemical, and mechanical stability, to effectively prevent direct contact between the surface of the lithium anode and the highly reactive reduced oxygen species (Li₂O₂ or its intermediate LiO₂) in cell. It is believed that the protection strategy describes here can be easily extended to other next‐generation high energy density batteries using metal as anode including Li–S and Na–O₂ batteries.     

A Highly Reversible Long‐Life Li–CO2 Battery with a RuP2‐Based Catalytic Cathode

Rechargeable Li–CO₂ batteries have attracted worldwide attention due to the capability of CO₂ capture and superhigh energy density. However, they still suffer from poor cycling performance and huge overpotential. Thus, it is essential to explore highly efficient catalysts to improve the electrochemical performance of Li–CO₂ batteries. Here, phytic acid (PA)‐cross‐linked ruthenium complexes and melamine are used as precursors to design and synthesize RuP₂ nanoparticles highly dispersed on N, P dual‐doped carbon films (RuP₂‐NPCFs), and the obtained RuP₂‐NPCF is further applied as the catalytic cathode for Li–CO₂ batteries. RuP₂ nanoparticles that are uniformly deposited on the surface of NPCF show enhanced catalytic activity to decompose Li₂CO₃ at low charge overpotential. In addition, the NPCF its with porous structure in RuP₂‐NPCF provides superior electrical conductivity, high electrochemical stability, and enough ion/electron and space for the reversible reaction in Li–CO₂ batteries. Hence, the RuP₂‐NPCF cathode delivers a superior reversible discharge capacity of 11951 mAh g^?1, and achieves excellent cyclability for more than 200 cycles with low overpotentials (<1.3 V) at the fixed capacity of 1000 mAh g^?1. This work paves a new way to design more effective catalysts for Li–CO₂ batteries.     

Graphene's Latest Cousin: Plumbene Epitaxial Growth on a “Nano WaterCube”

While theoretical studies predicted the stability and exotic properties of plumbene, the last group‐14 cousin of graphene, its realization has remained a challenging quest. Here, it is shown with compelling evidence that plumbene is epitaxially grown by segregation on a Pd_1?xPb_x(111) alloy surface. In scanning tunneling microscopy (STM), it exhibits a unique surface morphology resembling the famous Weaire–Phelan bubble structure of the Olympic “WaterCube” in Beijing. The “soap bubbles” of this “Nano WaterCube” are adjustable with their average sizes (in‐between 15 and 80 nm) related to the Pb concentration (x < 0.2) dependence of the lattice parameter of the Pd_1?xPb_x(111) alloy surface. Angle‐resolved core‐level measurements demonstrate that a lead sheet overlays the Pd_1?xPb_x(111) alloy. Atomic‐scale STM images of this Pb sheet show a planar honeycomb structure with a unit cell ranging from 0.48 to 0.49 nm corresponding to that of the standalone 2D topological insulator plumbene.