Alloyable Viscous Fluid for Interface Welding of Garnet Electrolyte to Enable Highly Reversible Fluoride Conversion Solid State Batteries

The garnet-type solid-state Li-metal batteries are promising to develop into the high-energy-density system when coupled with the high-capacity conversion reaction cathodes. However, the high interfacial resistance and poor contact between garnet electrolyte and Li anode are still a challenge. Here, an alloyable viscous fluid strategy is proposed for Li/garnet interface welding to enable highly reversible fluoride conversion solid-state batteries. The super-assembled phenide polymer with liquid metal property can serve as “oily” interlayer to in situ construct an ionic/electronic mixed conduction network by thermal and electrochemical lithiation. The resultant healing effect of contact voids between garnet and Li enables a dramatic reduction of interfacial resistance to 6 Ω cm². The confinement and compaction of conversion products by garnet electrolyte endow the FeF₃ based batteries with long-cycling and high-rate performance (520 and 330 mAh g⁻¹ at 0.2 and 2 C respectively). This ceramic configuration also endows the CuF₂ conversion battery with much better rechargeability (instead as widely known primary battery).     

An All‐Ceramic Solid‐State Rechargeable Na+‐Battery Operated at Intermediate Temperatures

A major challenge to the development of the next‐generation all‐solid‐state rechargeable battery technology is the inferior performance caused by insufficient ionic conductivity in the electrolyte and poor mixed ionic‐electronic conductivity in the electrodes. Here we demonstrate the utility of elevated temperature as an advantageous means of enhancing the conductivity in the electrolyte and promoting the catalytic activity at electrodes in an all‐ceramic rechargeable Na⁺‐battery. The new Na⁺‐battery consists of a 154‐μm thick Na‐β′′‐Al₂O₃ electrolyte membrane, a 22‐μm thick P₂‐Na_2/3[Fe_1/2Mn_1/2]O₂ cathode and 52‐μm thick Na₂Ti₃O₇‐La_0.8Sr_0.2MnO₃ composite anode. The battery is shown to be capable of producing a reversible and stable capacity of 152 mAhg^?1 at 350 °C. While the battery's achievable capacity is limited by the electrode materials employed, it does exhibit unique low self‐discharge rate, high tolerance to thermal cycling and an outstanding safety feature.     

Li batteries with porous sol–gel cathodes

The structure presented is a high-capacity micro battery, lithium based, consisting of porous cathode, solid electrolyte and silver anode. A spinel LiNi_0.4La_0.1Mn_1.5O₄ sol–gel layer was deposited on a porous ceramic substrate to give high specific surface to the chip-like microbatteries. The anode used was thermally evaporated Ag and the electrolyte a sol–gel hybrid Li₄SiO₄ layer.     

Artificial Graphite Paper as a Corrosion-Resistant Current Collector for Long-Life Lithium Metal Batteries

The employment of ultra-thin lithium metal anode with high loading cathode is the key to realizing high-energy-density rechargeable lithium batteries. Ultra-thin lithium foils are routinely loaded on a copper substrate in batteries, however, the close contact of these two metals causes galvanic corrosion in the presence of electrolyte, which results in irreversible consumption of lithium and decomposition of electrolyte. Herein, a lightweight and highly conductive flexible graphite paper (GP) is applied to replace Cu foil as the current collector for lithium metal anode. It is demonstrated that the application of GP prevents galvanic corrosion and maintains intimate and steady contact between Li foil and GP current collector during cycling, thereby improving the electrochemical performance of the battery. A 1.08 Ah pouch cell assembled with Li@GP anode and LiNi_0.8Co_0.1Mn_0.1O₂ cathode exhibits a long lifetime of 240 cycles with a capacity retention of 91.6% under limited Li, high cathode loading and lean electrolyte conditions.     

Armoring LiNi1/3Co1/3Mn1/3O2 Cathode with Reliable Fluorinated Organic–Inorganic Hybrid Interphase Layer toward Durable High Rate Battery

Ternary layered oxide materials have attracted extensive attention as a promising cathode candidate for high‐energy‐density lithium‐ion batteries. However, the undesirable electrochemical degradation at the electrode–electrolyte interface definitively shortens the battery service life. An effective and viable approach is proposed for improving the cycling stability of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode using lithium difluorophosphate (LiPO₂F₂) paired with fuoroethylene carbonate (FEC) as co‐additives into conventional electrolytes. It is found that the co‐additives can greatly reduce the interface charge transfer impedance and significantly extend the life span of LiNi_1/3Co_1/3Mn_1/3O₂//Li (NMC//Li) batteries. The developed cathode demonstrates exceptional capacity retention of 88.7% and remains structural integrity at a high current of 5C after 500 cycles. Fundamental mechanism study indicates a dense, stable fluorinated organic–inorganic hybrid cathode‐electrolyte interphase (CEI) film derived from LiPO₂F₂ in conjunction with FEC additives on the surface of NMC cathode material, which significantly suppresses the decomposition of electrolyte and mitigates the dissolution of transition metal ions. The interfacial engineering of the electrode materials stabilized by the additives manipulation provides valuable guidance for the development of advanced cathode materials.     

Efficient Synergism of Chemisorption and Wackenroder Reaction via Heterostructured La2O3-Ti3C2Tx -Embedded Carbon Nanofiber for High-Energy Lithium-Sulfur Pouch Cells

Lithium-sulfur (Li-S) batteries have been regarded as promising next-generation energy storage systems due to their high energy density and low cost, but their practical application is hindered by inferior long-cycle stability caused by the severe shuttle effect of lithium polysulfides (LiPSs) and sluggish reaction kinetics. This study reports a La₂O₃-MXene heterostructure embedded in carbon nanofiber (CNF) (denoted as La₂O₃-MXene@CNF) as a sulfur (S) host to address the above issues. The unique features of this heterostructure endow the sulfur host with synergistic catalysis during the charging and discharging processes. The strong adsorption ability provided by the La₂O₃ domain can capture sufficient LiPSs for the subsequent catalytic conversion, and the insoluble thiosulfate intermediate produced by hydroxyl terminal groups on the surface of MXene greatly promotes the rapid conversion of LiPSs to Li₂S via a “Wackenroder reaction.” Therefore, the S cathode with La₂O₃-MXene@CNF (La₂O₃-MXene@CNF/S) exhibits excellent cycling stability with a low capacity fading rate of 0.031% over 1000 cycles and a high capacity of 857.9 mAh g⁻¹ under extremely high sulfur loadings. Furthermore, a 5 Ah-level pouch cell is successfully assembled for stable cycling, which delivers a high specific energy of 341.6 Wh kg⁻¹ with a low electrolyte/sulfur ratio (E/S ratio).     

Low Resistance–Integrated All‐Solid‐State Battery Achieved by Li7La3Zr2O12 Nanowire Upgrading Polyethylene Oxide (PEO) Composite Electrolyte and PEO Cathode Binder

All‐solid‐state lithium metal battery is the most promising next‐generation energy storage device. However, the low ionic conductivity of solid electrolytes and high interfacial impedance with electrode are the main factors to limit the development of all‐solid‐state batteries. In this work, a low resistance–integrated all‐solid‐state battery is designed with excellent electrochemical performance that applies the polyethylene oxide (PEO) with lithium bis(trifluoromethylsulphonyl)imide as both binder of cathode and matrix of composite electrolyte embedded with Li₇La₃Zr₂O₁₂ (LLZO) nanowires (PLLN). The PEO in cathode and PLLN are fused at high temperature to form an integrated all‐solid‐state battery structure, which effectively strengthens the interface compatibility and stability between cathode and PLLN to guarantee high efficient ion transportation during long cycling. The LLZO nanowires uniformly distributed in PLLN can increase the ionic conductivity and mechanical strength of composite electrolyte efficiently, which induces the uniform deposition of lithium metal, thereby suppressing the lithium dendrite growth. The Li symmetric cells using PLLN can stably cycle for 1000 h without short circuit at 60 °C. The integrated LiFePO₄/PLLN/Li batteries show excellent cycling stability at both 60 and 45 °C. The study proposed a novel and robust battery structure with outstanding electrochemical properties.     

Adiponitrile (C6H8N2): A New Bi‐Functional Additive for High‐Performance Li‐Metal Batteries

Rechargeable batteries with a Li metal anode and Ni‐rich Li[Ni_xCo_yMn_1?x?y]O₂ cathode (Li/Ni‐rich NCM battery) have been emerging as promising energy storage devices because of their high‐energy density. However, Li/Ni‐rich NCM batteries have been plagued by the issue of the thermodynamic instability of the Li metal anode and aggressive surface chemistry of the Ni‐rich cathode against electrolyte solution. In this study, a bi‐functional additive, adiponitrile (C₆H₈N₂), is proposed which can effectively stabilize both the Li metal anode and Ni‐rich NCM cathode interfaces. In the Li/Ni‐rich NCM battery, the addition of 1 wt% adiponitrile in 0.8 m LiTFSI + 0.2 M LiDFOB + 0.05 M LiPF₆ dissolved in EMC/FEC = 3:1 electrolyte helps to produce a conductive and robust Li anode/electrolyte interface, while strong coordination between Ni⁴⁺ on the delithiated Ni‐rich cathode and nitrile group in adiponitrile reduces parasitic reactions between the electrolyte and Ni‐rich cathode surface. Therefore, upon using 1 wt% adiponitrile, the Li/full concentration gradient Li[Ni_0.73Co_0.10Mn_0.15Al_0.02]O₂ battery achieves an unprecedented cycle retention of 75% over 830 cycles under high‐capacity loading of 1.8 mAh cm^?2 and fast charge–discharge time of 2 h. This work marks an important step in the development of high‐performance Li/Ni‐rich NCM batteries with efficient electrolyte additives.     

Low Resistance and High Stable Solid–Liquid Electrolyte Interphases Enable High-Voltage Solid-State Lithium Metal Batteries

Solid-state batteries (SSBs) with addition of liquid electrolytes are considered to possibly replace the current lithium-ion batteries (LIBs) because they combine the advantages of benign interfacial contact and strong barriers for unwanted redox shuttles. However, solid electrolyte and liquid electrolyte are generally (electro)-chemically incompatible and the resistance of the newly formed solid–liquid electrolyte interphase (SLEI) appears as an additional contribution to the overall battery resistance. Herein, a boron, fluorine-donating liquid electrolyte (B, F-LE) is introduced into the interface between the high-voltage cathode and ultrathin composite solid electrolyte (CSE), which is fabricated by adhering a high content of nanosized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), to generate a low resistance and high stable SLEI in situ, giving a stable high-voltage output with a reinforced cathode|CSE interface. B, F-LE, consisting of a highly fluorinated electrolyte with a lithium bis(oxalato)borate additive, exhibits good chemical compatibility with CSE and enables rapid and uniform transportation of Li⁺, with its electrochemically and chemically stable interface for high-voltage cathode. Eventually, the B, F-LE assisted LiNi_0.6Co_0.2Mn_0.2O₂|Li battery displays the enhanced rate capability and high voltage cycling stability. The findings provide an interfacial engineering strategy to turn SLEI from a “real culprit” into the “savior” that may pave a brand-new way to manipulate SLEI chemistry in hybrid solid–liquid devices.     

A High‐Energy Li‐Ion Battery Using a Silicon‐Based Anode and a Nano‐Structured Layered Composite Cathode

High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni‐rich Li[Ni_0.75Co_0.1Mn_0.15]O₂, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C‐IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C‐IWGS anode delivers a high capacity of >800 mAh g^?1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (～6 wt%). The cathode (Li[Ni_0.75Co_0.1Mn_0.15]O₂) is structurally optimized (Ni‐rich core and a Ni‐depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g^?1) with excellent stability at high voltage (～4.3 V). A novel lithium ion battery system based on the Si/C‐IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg^?1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.     

A Universal Strategy Toward Low-Cost Aqueous Sulfur–Iodine Batteries

Rechargeable aqueous batteries with non-toxic and non-flammable features are promising candidates for large-scale energy storage. However, their practical applications are impeded by the insufficient electrochemical stability windows of aqueous electrolytes and intrinsic drawbacks of current electrodes. Herein, an aqueous sulfur–iodine chemistry that can be deployed in aqueous battery systems by employing water-in-bisalt (WiBS) electrolyte, sulfur composite anode, and iodine composite cathode is demonstrated. The freestanding iodine/carbon cloth cathode and halide-containing WiBS electrolyte can support the continuous I⁺/I⁰ reaction by forming interhalogen. Meanwhile, the highly-concentrated electrolyte and inorganic-based solid electrolyte interphase can effectively suppress the dissolution/diffusion of polysulfides, thus realizing S/S_x²⁻ conversion reactions on the anode. Therefore, the as-assembled aqueous sulfur–iodine batteries based on S/S_x²⁻ and I⁺/I⁰ redox couples can deliver a high energy density of 158.7 Wh kg⁻¹ with a considerable cycling performance and safety. Furthermore, this chemistry can be further extended to multivalent ion-based battery systems. As demonstration models, Ca-based and Al-based aqueous sulfur–iodine batteries are also fabricated, which provide a new avenue towards the development of aqueous batteries for low-cost and highly safe energy storage.     

“Water-in-Deep Eutectic Solvent” Electrolytes for High-Performance Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries have been considered as promising alternatives to Li-ion batteries due to their abundant reserves, low price, and high safety. However, Zn anode shows poor reversibility and cycling stability in most conventional aqueous electrolytes. Here, a new type of aqueous Zn-ion electrolyte based on ZnCl₂–acetamide deep eutectic solvent with both environmental and economic friendliness has been prepared. The water molecule introduced in the “water-in-deep eutectic solvent” electrolyte could reduce the Zn²⁺ desolvation energy barrier by regulating Zn²⁺ solvation structure to promote uniform Zn nucleation. Zn anode shows improved electrochemical performance (≈98% Coulombic efficiency over 1000 cycles) in the electrolyte whose molar ratio of ZnCl₂:acetamide:H₂O is 1:3:1. The assembled full battery composed of phenazine cathode and Zn anode could stably cycle over 10 000 cycles with a high capacity retention of 85.7%. Overall, this work offers new insights into exploring new green electrolyte systems for Zn-ion batteries.     

An Intrinsically Nonflammable Electrolyte for Prominent-Safety Lithium Metal Batteries with High Energy Density and Cycling Stability

Nex-generation high-energy-density storage battery, assembled with lithium (Li)-metal anode and nickel-rich cathode, puts forward urgent demand for advanced electrolytes that simultaneously possess high security, wide electrochemical window, and good compatibility with electrode materials. Herein an intrinsically nonflammable electrolyte is designed by using 1 M lithium difluoro(oxalato)borate (LiDFOB) in triethyl phosphate (TEP) and N-methyl-N-propyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr₁₃][TFSI] ionic liquid (IL) solvents. The introduction of IL can bring plentiful organic cations and anions, which provides a cation shielding effect and regulates the Li⁺ solvation structure with plentiful Li⁺-DFOB⁻ and Li⁺-TFSI⁻ complexes. The unique Li⁺ solvation structure can induce stable anion-derived electrolyte/electrode interphases, which effectively inhibit Li dendrite growth and suppress side reactions between TEP and electrodes. Therefore, the LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90)/Li coin cell with this electrolyte can deliver stable cycling even under 4.5 V and 60 °C. Moreover, a Li-metal battery with thick NCM90 cathode (≈ 15 mg cm⁻²) and thin Li-metal anode (≈ 50 µm) (N/P ≈ 3), also reveals stable cycling performance under 4.4 V. And a 2.2 Ah NCM90/Li pouch cell can simultaneously possess prominent safety with stably passing the nail penetration test, and high gravimetric energy density of 470 Wh kg⁻¹ at 4.4 V.     

Cubic Perovskite Fluoride as Open Framework Cathode for Na‐Ion Batteries

Exploring novel structure prototype and mineral phase, especially open framework material, is crucial to developing high‐performance Na‐ion battery cathodes in view of potentially faster intrinsic diffusion of Na⁺ in lattices. Perovskite phases have been widely applied in solar cells, fuel cells, and electrocatalysis; however, they are rarely attempted as energy storage electrode materials. This study proposes pre‐expanding perovskite iron fluoride (KFeF₃) framework by stuffing large‐sized K⁺ as a channel filler, which is advantageous over Na⁺, NH₄⁺, and H₂O molecule filler in terms of structure robustness, symmetry, and connectivity. K⁺ stuffing leads to the preservation of a more “regular” cubic phase with fast isotropic 3D diffusion as a consequence of no distortion of FeF₆ octahedra during K‐Na electrochemical exchange and following Na‐insertion cycling. High‐rate Na‐storage is achievable with a reversible capacity of 110, 70, and 40 mAh g^?1 at 0.1, 2, and 10 C, respectively, for this open framework fluoride cathode, benefiting from solid solution electrochemical behavior and high intrinsic diffusion coefficient. It is thought that this rate performance is currently the best among Na‐storage fluoride materials.     

An Aqueous Mg2+-Based Dual-Ion Battery with High Power Density

Rechargeable Mg batteries promise low-cost, safe, and high-energy alternatives to Li-ion batteries. However, the high polarization strength of Mg²⁺ leads to its strong interaction with electrode materials and electrolyte molecules, resulting in sluggish Mg²⁺ dissociation and diffusion as well as insufficient power density and cycling stability. Here an aqueous Mg²⁺-based dual-ion battery is reported to bypass the penalties of slow dissociation and solid-state diffusion. This battery chemistry utilizes fast redox reactions on the polymer electrodes, i.e., anion (de)doping on the polyaniline (PANI) cathode and (de)enolization upon incorporating Mg²⁺ on the polyimide anode. The kinetically favored and stable electrodes depend on designing a saturated aqueous electrolyte of 4.5 m Mg(NO₃)₂. The concentrated electrolyte suppresses the irreversible deprotonation reaction of the PANI cathode to enable excellent stability (a lifespan of over 10 000 cycles) and rate performance (33% capacity retention at 500 C) and avoids the anodic parasitic reaction of nitrate reduction to deliver the stable polyimide anode (86.2% capacity retention after 6000 cycles). The resultant full Mg²⁺-based dual-ion battery shows a high specific power of 10 826 W kg⁻¹, competitive with electrochemical supercapacitors. The electrolyte and electrode chemistries elucidated in this study provide an alternative approach to developing better-performing Mg-based batteries.     

Conformal Multifunctional Titania Shell on Iron Oxide Nanorod Conversion Electrode Enables High Stability Exceeding 30 000 Cycles in Aqueous Electrolyte

Iron oxide is promising for use in aqueous energy storage devices due to the high capacity, but one of the most challenging problems is cycling instability within the large potential window that results from the complete quasi‐conversion reaction. Herein, a conformal surface coating strategy toward iron oxide via atomic layer deposition (ALD) is presented and an Fe₃O₄@TiO₂ core–shell nanorod array anode is reported that exhibits remarkable cycling performance exceeding 30 000 times within a wide potential window in neutral lithium salt electrolyte. ALD offers a uniform and precisely controllable TiO₂ shell that not only buffers the inner volume expansion of Fe₃O₄, but also contributes extra capacity through Li⁺ intercalation/de‐intercalation and helps to alleviate the water electrolysis. Furthermore, by pairing with a pseduocapacitive cathode of V₂O₃@carbon and using a hydrogel electrolyte of PVA‐LiCl, a unique flexible quasi‐solid‐state hybrid supercapacitor can be assembled. With a high voltage of 2.0 V, the device delivers high volumetric energy and power densities (2.23 mWh cm^?3, 1090 mW cm^?3), surpassing many recently reported flexible supercapacitors. This work highlights the importance of ALD conformal multifunctional shell to instable nanoarray electrodes in aqueous electrolytes and brings new opportunities to design advanced aqueous hybrid energy storage devices.     

Self‐Standing Porous LiCoO2 Nanosheet Arrays as 3D Cathodes for Flexible Li‐Ion Batteries

Self‐standing electrodes are the key to realize flexible Li‐ion batteries. However, fabrication of self‐standing cathodes is still a major challenge. In this work, porous LiCoO₂ nanosheet arrays are grown on Au‐coated stainless steel (Au/SS) substrates via a facile “hydrothermal lithiation” method using Co₃O₄ nanosheet arrays as the template followed by quick annealing in air. The binder‐free and self‐standing LiCoO₂ nanosheet arrays represent the 3D cathode and exhibit superior rate capability and cycling stability. In specific, the LiCoO₂ nanosheet array electrode can deliver a high reversible capacity of 104.6 mA h g^?1 at 10 C rate and achieve a capacity retention of 81.8% at 0.1 C rate after 1000 cycles. By coupling with Li₄Ti₅O₁₂ nanosheet arrays as anode, an all‐nanosheet array based LiCoO₂//Li₄Ti₅O₁₂ flexible Li‐ion battery is constructed. Benefiting from the 3D nanoarchitectures for both cathode and anode, the flexible LiCoO₂//Li₄Ti₅O₁₂ battery can deliver large specific reversible capacities of 130.7 mA h g^?1 at 0.1 C rate and 85.3 mA h g^?1 at 10 C rate (based on the weight of cathode material). The full cell device also exhibits good cycling stability with 80.5% capacity retention after 1000 cycles at 0.1 C rate, making it promising for the application in flexible Li‐ion batteries.     

Intercalated Electrolyte with High Transference Number for Dendrite‐Free Solid‐State Lithium Batteries

Solid‐state lithium (Li) batteries using solid electrolytes and Li anodes are highly desirable because of their high energy densities and intrinsic safety. However, low ambient‐temperature conductivity and poor interface compatibility of solid electrolytes as well as Li dendrite formation cause large polarization and poor cycling stability. Herein, a high transference number intercalated composite solid electrolyte (CSE) is prepared by the combination of a solution‐casting and hot‐pressing method using layered lithium montmorillonite, poly(ethylene carbonate), lithium bis(fluorosulfonyl)imide, high‐voltage fluoroethylene carbonate additive, and poly(tetrafluoroethylene) binder. The electrolyte presents high ionic conductivity (3.5 × 10^?4 S cm^?1), a wide electrochemical window (4.6 V vs Li⁺/Li), and high ionic transference number (0.83) at 25 °C. In addition, a 3D Li anode is also fabricated via a facile thermal infusion strategy. The synergistic effect of high transference number intercalated electrolyte and 3D Li anode is more favorable to suppress Li dendrites in a working battery. The solid‐state batteries based on LiFePO₄ (Al₂O₃ @ LiNi_0.5Co_0.2Mn_0.3O₂), CSE, and 3D Li deliver admirable cycling stability with discharge capacity 145.9 mAh g^?1 (150.7 mAh g^?1) and capacity retention 91.9% after 200 cycles at 0.5 C (92.0% after 100 cycles at 0.2 C) at 25 °C. This work affords a splendid strategy for high‐performance solid‐state battery.     

On the Cycling Performance of Na‐O2 Cells: Revealing the Impact of the Superoxide Crossover toward the Metallic Na Electrode

Na‐O₂ batteries have attracted extensive attention as promising candidates for large‐scale energy storage due to their ultrahigh theoretical energy density. However, the poor cycling performance of Na‐O₂ batteries is one of the major challenges facing its future development. A novel Na‐O₂ battery using electrically connected carbon paper with Na metal as a protected anode is presented in this study. The O₂^? crossover from the cathode to anode partially contributes to the limited Coulombic efficiency, as well as the Na corrosion during the cycling process. For the cells with protected Na, the carbon paper maintains a pseudo‐equal potential with the Na metal and works as an artificial protective layer to suppress the detrimental side reactions caused by O₂^? and O₂ crossover toward the Na electrode. Furthermore, the short‐circuiting issue caused by Na dendrite growth also can be completely resolved. Consequently, the Na‐O₂ cells with protected Na exhibit two times higher discharge capacity and cycling stability compared with the cells using bare Na. These results indicate the crucial role of the Na anode in determining the overall cell performance and a rational design of anode can dramatically contribute to develop advanced Na‐O₂ batteries with longer lifespans and better cycling performance.     

Liquid-State Cathode Enabling a High-Voltage and Air-Stable Fe-Al Hybrid Battery

Aluminum (Al) is an ideal anode material in low-cost battery system for energy storage, with high theoretical capacities. However, the sluggish Al³⁺-involved kinetics challenges the selection of common cathode materials (Al³⁺ intercalation or conversion). Herein, a redox-active Fe–Cl complex serves as the liquid-state cathode to couple with a low-cost Al anode, which synergizes the advantages of redox flow batteries and Al rechargeable batteries. The interplay of Fe-Cl coordinated formula and electrochemical properties are revealed for the first time. It is found that [Fe₂Cl₇]⁻ molecule has a high voltage versus Al anode (1.3 V), and the novel Fe-Al hybrid battery fulfills a capacity of 1.6 mAh cm⁻² (20 Ah L⁻¹) record high in a coin cell among Al-based batteries. Furthermore, the energy efficiency, which is a vital parameter to evaluate the energy cost of the energy storage technology, reaches 85% (superior to most Al-based batteries) and an average of 70% over ≈900 h cycling. Particularly, the unique air-stable character enables normal operation of the battery assembled in ambient air. This work establishes a new application scenario for Al anode toward low-cost large-scale energy storage.