Molten‐NaNH2 Densified Graphene with In‐Plane Nanopores and N‐Doping for Compact Capacitive Energy Storage

Capacitive carbons are attractive for energy storage on account of their superior rate and cycling performance over traditional battery materials, but they usually suffer from a far lower volumetric energy density. Starting with expanded graphene, a simple, multifunctional molten sodium amide treatment for the preparation of high‐density graphene with high capacitive performance in both aqueous and lithium battery electrolytes is reported. The molten sodium amide can condense the expanded graphene, lead to nitrogen doping and, what is more important, create moderate in‐plane nanopores on graphene to serve as ion access shortcuts in dense graphene stacks. The resulting high‐density graphene electrode can deliver a volumetric capacitance of 522 F cm^?3 in a potassium hydroxide electrolyte; and in a lithium‐ion battery electrolyte, it exhibits a gravimetric and volumetric energy density of 618 W h kg^?1 and 740 W h L^?1, respectively, and even outperforms commercial LiFePO₄.     

A Flexible Solid‐State Aqueous Zinc Hybrid Battery with Flat and High‐Voltage Discharge Plateau

The migration of zinc‐ion batteries from alkaline electrolyte to neutral or mild acidic electrolyte promotes research into their flexible applications. However, discharge voltage of many reported zinc‐ion batteries is far from satisfactory. On one hand, the battery voltage is substantially restricted by the narrow voltage window of aqueous electrolytes. On the other hand, many batteries yield a low‐voltage discharge plateau or show no plateau but capacitor‐like sloping discharge profiles. This impacts the battery's practicability for flexible electronics where stable and consistent high energy is needed. Herein, an aqueous zinc hybrid battery based on a highly concentrated dual‐ion electrolyte and a hierarchically structured lithium‐ion‐intercalative LiVPO₄F cathode is developed. This hybrid battery delivers a flat and high‐voltage discharge plateau of nearly 1.9 V, ranking among the highest reported values for all aqueous zinc‐based batteries. The resultant high energy density of 235.6 Wh kg^?1 at a power density of 320.8 W kg^?1 also outperforms most reported zinc‐based batteries. A designed solid‐state and long‐lasting hydrogel electrolyte is subsequently applied in the fabrication of a flexible battery, which can be integrated into various flexible devices as powerful energy supply. The idea of designing such a hybrid battery offers a new strategy for developing high‐voltage and high‐energy aqueous energy storage systems.     

A Composite Gel–Polymer/Glass–Fiber Electrolyte for Sodium‐Ion Batteries

An integrated preparation of a low‐cost composite gel–polymer/glass–fiber electrolyte with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) reinforced by a glass–fiber paper and modified by a polydopamine coating to tune the mechanical and surface properties of PVDF‐HFP is shown to be applicable to a sodium‐ion battery. The composite polymer matrix exhibits excellent mechanical strength and thermal stability up to 200 °C. After saturating with a liquid electrolyte, a wide electrochemical window and high ionic conductivity is obtained for the composite gel–polymer/glass–fiber electrolyte. When tested in a sodium‐ion battery with Na₂MnFe(CN)₆ as cathode, the rate capability, cycling performance, and coulombic efficiency are significantly improved. The results suggest that the composite polymer electrolyte is a very attractive separator for a large‐scale battery system where safety and cost are the main concerns.     

A Sodium‐Ion Battery with a Low‐Cost Cross‐Linked Gel‐Polymer Electrolyte

The design of a sodium‐ion rechargeable battery with an antimony anode, a Na₃V₂(PO₄)₃ cathode, and a low‐cost composite gel‐polymer electrolyte based on cross‐linked poly(methyl methacrylate) is reported. The application of an antimony anode, on replacement of the sodium metal that is commonly used in sodium‐ion half‐cells, reduces significantly the interfacial resistance and charge transfer resistance of a sodium‐ion battery, which enables a smaller polarization for a sodium‐ion full‐cell Sb/Na₃V₂(PO₄)₃ running at relatively high charge and discharge rates. The incorporation of the gel‐polymer electrolyte is beneficial to maintain stable interfaces between the electrolyte and the electrodes of the sodium‐ion battery at elevated temperature. When running at 60 °C, the sodium‐ion full‐cell Sb/Na₃V₂(PO₄)₃ with the gel‐polymer electrolyte exhibits superior cycling stability compared to a battery with the conventional liquid electrolyte.     

A Pair of NiCo2O4 and V2O5 Nanowires Directly Grown on Carbon Fabric for Highly Bendable Lithium‐Ion Batteries

Mechanically bendable and flexible functionalities are urgently required for next‐generation battery systems that will be included in soft and wearable electronics, active sportswear, and origami‐based deployable space structures. However, it is very difficult to synthesize anode and cathode electrodes that have high energy density and structural reliability under large bending deformation. Here, vanadium oxide (V₂O₅) and nickel cobalt oxide (NiCo₂O₄) nanowire‐carbon fabric electrodes for highly flexible and bendable lithium ion batteries are reported. The vanadium oxide and nickel cobalt oxide nanowires were directly grown on plasma‐treated carbon fabric and were used as cathode and anode electrodes in a full cell lithium ion battery. Most importantly, a pre‐lithiation process was added to the nickel cobalt oxide nanowire anode to facilitate the construction of a full cell using symmetrically‐architectured nanowire‐carbon fabric electrodes. The highly bendable full cell based on poly(ethylene oxide) polymer electrolyte and room temperature ionic liquid shows high energy density of 364.2 Wh kg^?1 at power density of 240 W kg^?1, without significant performance degradation even under large bending deformations. These results show that vanadium oxide and lithiated nickel cobalt oxide nanowire‐carbon fabrics are a good combination for binder‐free electrodes in highly flexible lithium‐ion batteries.     

Scalable Water‐Based Production of Highly Conductive 2D Nanosheets with Ultrahigh Volumetric Capacitance and Rate Capability

Highly conductive and ultrathin 2D nanosheets are of importance for the development of portable electronics and electric vehicles. However, scalable production and rational design for highly electronic and ionic conductive 2D nanosheets still remain a challenge. Herein, an industrially adoptable fluid dynamic exfoliation process is reported to produce large quantities of ionic liquid (IL)‐functionalized metallic phase MoS₂ (m‐MoS₂) and defect‐free graphene (Gr) sheets. Hybrid 2D–2D layered films are also fabricated by incorporating Gr sheets into compact m‐MoS₂ films. The incorporated IL functionalities and Gr sheets prevent aggregation and restacking of the m‐MoS₂ sheets, thereby creating efficient and rapid ion and electron pathways in the hybrid films. The hybrid film with a high packing density of 2.02 g cm^?3 has an outstanding volumetric capacitance of 1430.5 F cm^?3 at 1 A g^?1 and an extremely high rate capability of 80% retention at 1000 A g^?1. The flexible supercapacitor assembled using a polymer‐gel electrolyte exhibits excellent resilience to harsh electrochemical and mechanical conditions while maintaining an impressive rate performance and long cycle life. Successful achievement of an ultrahigh volumetric energy density (1.14 W h cm^?3) using an organic electrolyte with a wide cell voltage of ≈3.5 V is demonstrated.     

Single‐Ion Conducting Electrolyte Based on Electrospun Nanofibers for High‐Performance Lithium Batteries

Herein, a novel electrospun single‐ion conducting polymer electrolyte (SIPE) composed of nanoscale mixed poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) and lithium poly(4,4′‐diaminodiphenylsulfone, bis(4‐carbonyl benzene sulfonyl)imide) (LiPSI) is reported, which simultaneously overcomes the drawbacks of the polyolefin‐based separator (low porosity and poor electrolyte wettability and thermal dimensional stability) and the LiPF₆ salt (poor thermal stability and moisture sensitivity). The electrospun nanofiber membrane (es‐PVPSI) has high porosity and appropriate mechanical strength. The fully aromatic polyamide backbone enables high thermal dimensional stability of es‐PVPSI membrane even at 300 °C, while the high polarity and high porosity ensures fast electrolyte wetting. Impregnation of the membrane with the ethylene carbonate (EC)/dimethyl carbonate (DMC) (v:v = 1:1) solvent mixture yields a SIPE offering wide electrochemical stability, good ionic conductivity, and high lithium‐ion transference number. Based on the above‐mentioned merits, Li/LiFePO₄ cells using such a SIPE exhibit excellent rate capacity and outstanding electrochemical stability for 1000 cycles at least, indicating that such an electrolyte can replace the conventional liquid electrolyte–polyolefin combination in lithium ion batteries (LIBs). In addition, the long‐term stripping–plating cycling test coupled with scanning electron microscope (SEM) images of lithium foil clearly confirms that the es‐PVPSI membrane is capable of suppressing lithium dendrite growth, which is fundamental for its use in high‐energy Li metal batteries.     

High‐Energy‐Density Foldable Battery Enabled by Zigzag‐Like Design

Flexible batteries, seamlessly compatible with flexible and wearable electronics, attract a great deal of research attention. Current designs of flexible batteries struggle to meet one of the most extreme yet common deformation scenarios in practice, folding, while retaining high energy density. Inspired by origami folding, a novel strategy to fabricate zigzag‐like lithium ion batteries with superior foldability is proposed. The battery structure could approach zero‐gap between two adjacent energy storage segments, achieving an energy density that is 96.4% of that in a conventional stacking cell. A foldable battery thus fabricated demonstrates an energy density of 275 Wh L^?1 and is resilient to fatigue over 45 000 dynamic cycles with a folding angle of 130°, while retaining stable electrochemical performance. Additionally, the power stability and resilience to nail shorting of the foldable battery are also examined.     

Stable Seamless Interfaces and Rapid Ionic Conductivity of Ca–CeO2/LiTFSI/PEO Composite Electrolyte for High‐Rate and High‐Voltage All‐Solid‐State Battery

Stable and seamless interfaces among solid components in all‐solid‐state batteries (ASSBs) are crucial for high ionic conductivity and high rate performance. This can be achieved by the combination of functional inorganic material and flexible polymer solid electrolyte. In this work, a flexible all‐solid‐state composite electrolyte is synthesized based on oxygen‐vacancy‐rich Ca‐doped CeO₂ (Ca–CeO₂) nanotube, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and poly(ethylene oxide) (PEO), namely Ca–CeO₂/LiTFSI/PEO. Ca–CeO₂ nanotubes play a key role in enhancing the ionic conductivity and mechanical strength while the PEO offers flexibility and assures the stable seamless contact between the solid electrolyte and the electrodes in ASSBs. The as‐prepared electrolyte exhibits high ionic conductivity of 1.3 × 10^?4 S cm^?1 at 60 °C, a high lithium ion transference number of 0.453, and high‐voltage stability. More importantly, various electrochemical characterizations and density functional theory (DFT) calculations reveal that Ca–CeO₂ helps dissociate LiTFSI, produce free Li ions, and therefore enhance ionic conductivity. The ASSBs based on the as‐prepared Ca–CeO₂/LiTFSI/PEO composite electrolyte deliver high‐rate capability and high‐voltage stability.     

Flexible,Scalable, and Highly Conductive Garnet‐Polymer Solid Electrolyte Templated by Bacterial Cellulose

Solid‐state electrolytes are a promising candidate for the next‐generation lithium‐ion battery, as they have the advantages of eliminating the leakage hazard of liquid solvent and elevating stability. However, inherent limitations such as the low ionic conductivity of solid polymer electrolytes and the high brittleness of inorganic ceramic electrolytes severally impede their practical application. Here, an inexpensive, facile, and scalable strategy to fabricate a hybrid Li₇La₃Zr₂O₁₂ (LLZO) and poly(ethylene oxide)‐based electrolyte by exploiting bacterial cellulose as a template is reported. The well‐organized LLZO network significantly enhances the ionic conductivity by extending long transport pathways for Li ions, exhibiting an elevated conductivity of 1.12 × 10^?4 S cm^?1. In addition, the hybrid electrolyte presents a structural flexibility, with minor impedance increase after bending. The facile and applicable approach establishes new principles for the strategy of designing scalable and flexible hybrid polymer electrolytes that can be utilized for high‐energy‐density batteries.     

Iron‐Oxide‐Based Advanced Anode Materials for Lithium‐Ion Batteries

Iron oxides, such as Fe₂O₃ and Fe₃O₄, have recently received increased attention as very promising anode materials for rechargeable lithium‐ion batteries (LIBs) because of their high theoretical capacity, non‐toxicity, low cost, and improved safety. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, recent research progress in the rational design and synthesis of diverse iron oxide‐based nanomaterials and their lithium storage performance for LIBs, including 1D nanowires/rods, 2D nanosheets/flakes, 3D porous/hierarchical architectures, various hollow structures, and hybrid nanostructures of iron oxides and carbon (including amorphous carbon, carbon nanotubes, and graphene). By focusing on synthesis strategies for various iron‐oxide‐based nanostructures and the impacts of nanostructuring on their electrochemical performance, novel approaches to the construction of iron‐oxide‐based nanostructures are highlighted and the importance of proper structural and compositional engineering that leads to improved physical/chemical properties of iron oxides for efficient electrochemical energy storage is stressed. Iron‐oxide‐based nanomaterials stand a good chance as negative electrodes for next generation LIBs.     

High‐Energy Aqueous Lithium Batteries

Owing to the high voltage of lithium‐ion batteries (LIBs), the dominating electrolyte is non‐aqueous. The idea of an aqueous rechargeable lithium battery (ARLB) dates back to 1994, but it had attracted little attention due to the narrow stable potential window of aqueous electrolytes, which results in low energy density. However, aqueous electrolytes were employed during the 2000s for the fundamental studies of electrode materials in the absence of side reactions such as the decomposition of organic species. The high solubility of lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in water has introduced new opportunities for high‐voltage ARLBs. Nonetheless, these ideas are somehow overshadowed by the common perception about the essential limitation of the aqueous electrolyte. The electrochemical behaviour of conventional electrode materials can be substantially tuned in the water‐in‐salt electrolytes. The latest idea of utilising a graphite anode in the aqueous water‐in‐salt electrolytes has paved the way towards not only 4‐V ARLB but also a new generation of Li?S batteries with a higher operating voltage and energy efficiency. Furthermore, aqueous electrolytes can provide a cathodically stable environment for Li?O₂ batteries. The present paper aims to highlight these emerging opportunities possibly leading to a new generation of LIBs, which can be substantially cheaper and safer.     

K‐Ion Storage Enhancement in Sb2O3/Reduced Graphene Oxide Using Ether‐Based Electrolyte

In this work, an ether‐based electrolyte is adopted instead of conventional ester‐based electrolyte for an Sb₂O₃‐based anode and its enhancement mechanism is unveiled for K‐ion storage. The anode is fabricated by anchoring Sb₂O₃ onto reduced graphene oxide (Sb₂O₃‐RGO) and it exhibits better electrochemical performance using an ether‐based electrolyte than that using a conventional ester‐based electrolyte. By optimizing the concentration of the electrolyte, the Sb₂O₃‐RGO composite delivers a reversible specific capacity of 309 mAh g^?1 after 100 cycles at 100 mA g^?1. A high specific capacity of 201 mAh g^?1 still remains after 3300 cycles (111 days) at 500 mA g^?1 with almost no decay, exhibiting a longer cycle life compared with other metallic oxides. In order to further reveal the intrinsic mechanism, the energy changes for K atom migrating from surface into the sublayer of Sb₂O₃ are explored by density functional theory calculations. According to the result, the battery using the ether‐based electrolyte exhibits a lower energy change and migration barrier than those using other electrolytes for K‐ion, which is helpful to improve the K‐ion storage performance. It is believed that the work can provide deep understanding and new insight to enhance electrochemical performance using ether‐based electrolytes for KIBs.     

Pseudo‐Zn–Air and Zn‐Ion Intercalation Dual Mechanisms to Realize High‐Areal Capacitance and Long‐Life Energy Storage in Aqueous Zn Battery

Aqueous zinc batteries are considered as promising alternatives to lithium ion batteries owing to their low cost and high safety. However, the developments of state‐of‐the‐art zinc‐ion batteries (ZIB) and zinc–air batteries (ZAB) are limited by the unsatisfied capacities and poor cycling stabilities, respectively. It is of significance in utilizing the long‐cycle life of ZIB and high capacity of ZAB to exploit advanced energy storage systems. Herein, a bulk composite of graphene oxide and vanadium oxide (V₅O₁₂·6H₂O) as cathode material for aqueous Zn batteries in a mild electrolyte is employed. The battery performance is demonstrated to arise from a combination of the reversible cations insertion/extraction in vanadium oxide and especially the electrochemical redox reactions on the surface functional groups of graphene oxide (named as pseudo‐Zn–air mechanism). Along with adjusting the hydroxyl content on the surface of graphene oxide, the specific capacity is significantly increased from 342 mAh g^?1 to a maximum of 496 mAh g^?1 at 100 mA g^?1. The surface‐controlled kinetics occurring in the bulk composite ensure a high areal capacity of 10.6 mAh cm^?2 at a mass loading of 26.5 mg cm^?2, and a capacity retention of 84.7% over 10 000 cycles at a high current density of 10 A g^?1.     

Advanced Electrolytes for Fast‐Charging High‐Voltage Lithium‐Ion Batteries in Wide‐Temperature Range

LiNi_xMn_yCo_1?x?yO₂ (NMC) cathode materials with Ni ≥ 0.8 have attracted great interest for high energy‐density lithium‐ion batteries (LIBs) but their practical applications under high charge voltages (e.g., 4.4 V and above) still face significant challenges due to severe capacity fading by the unstable cathode/electrolyte interface. Here, an advanced electrolyte is developed that has a high oxidation potential over 4.9 V and enables NMC811‐based LIBs to achieve excellent cycling stability in 2.5–4.4 V at room temperature and 60 °C, good rate capabilities under fast charging and discharging up to 3C rate (1C = 2.8 mA cm^?2), and superior low‐temperature discharge performance down to ?30 °C with a capacity retention of 85.6% at C/5 rate. It is also demonstrated that the electrode/electrolyte interfaces, not the electrolyte conductivity and viscosity, govern the LIB performance. This work sheds light on a very promising strategy to develop new electrolytes for fast‐charging high‐energy LIBs in a wide‐temperature range.     

Two‐Dimensional Materials for Beyond‐Lithium‐Ion Batteries

Lithium‐ion batteries (LIBs) have dominated the portable electronics industry and solid‐state electrochemical research and development for the past two decades. In light of possible concerns over the cost and future availability of lithium, sodium‐ion batteries (SIBs) and other new technologies have emerged as candidates for large‐scale stationary energy storage. Research in these technologies has increased dramatically with a focus on the development of new materials for both the positive and negative electrodes that can enhance the cycling stability, rate capability, and energy density. Two‐dimensional (2D) materials are showing promise for many energy‐related applications and particularly for energy storage, because of the efficient ion transport between the layers and the large surface areas available for improved ion adsorption and faster surface redox reactions. Recent research highlights on the use of 2D materials in these future ‘beyond‐lithium‐ion’ battery systems are reviewed, and strategies to address challenges are discussed as well as their prospects.     

An Antiaging Electrolyte Additive for High‐Energy‐Density Lithium‐Ion Batteries

High‐capacity Li‐rich layered oxide cathodes along with Si‐incorporated graphite anodes have high reversible capacity, outperforming the electrode materials used in existing commercial products. Hence, they are potential candidates for the development of high‐energy‐density lithium‐ion batteries (LIBs). However, structural degradation induced by loss of interfacial stability is a roadblock to their practical use. Here, the use of malonic acid‐decorated fullerene (MA‐C₆₀) with superoxide dismutase activity and water scavenging capability as an electrolyte additive to overcome the structural instability of high‐capacity electrodes that hampers the battery quality is reported. Deactivation of PF₅ by water scavenging leads to the long‐term stability of the interfacial structures of electrodes. Moreover, an MA‐C₆₀‐added electrolyte deactivates the reactive oxygen species and constructs an electrochemically robust cathode‐electrolyte interface for Li‐rich cathodes. This work paves the way for new possibilities in the design of electrolyte additives by eliminating undesirable reactive substances and tuning the interfacial structures of high‐capacity electrodes in LIBs.     

Toward a High‐Performance All‐Plastic Full Battery with a'Single Organic Polymer as Both Cathode and Anode

The design and fabrication of high‐performance all‐plastic batteries is essentially important to achieve future flexible electronics. A major challenge in this field is the lack of stable and reliable soft organic electrodes with satisfactory performance. Here, a novel all‐plastic‐electrode based Li‐ion battery with a single flexible bi‐functional ladderized heterocyclic poly(quinone), (C₆O₂S₂)_n, as both cathode and anode is demonstrated. Benefiting from its unique ladder‐like quinone and dithioether structure, the as‐prepared polymer cathode shows a high energy density of 624 Wh kg^?1 (vs lithium anode) and a stable battery life of 1000 cycles. Moreover, the as‐fabricated symmetric full‐battery delivers a large capacity of 249 mAh g^?1 (at 20 mA g^?1), a good capacity retention of 119 mAh g^?1 after 250 cycles (at 1.0 A g^?1) and a noteworthy energy density up to 276 Wh kg^?1. The superior performance of poly(2,3‐dithiino‐1,4‐benzoquinone)‐based electrode rivals most of the state‐of‐the‐art demonstrations on organic‐based metal‐ion shuttling batteries. The study provides an effective strategy to develop stable bi‐functional electrode materials toward the next‐generation of high performance all‐plastic batteries.     

High‐Performance Silicon Anodes Enabled By Nonflammable Localized High‐Concentration Electrolytes

Silicon anodes are regarded as one of the most promising alternatives to graphite for high energy‐density lithium‐ion batteries (LIBs), but their practical applications have been hindered by high volume change, limited cycle life, and safety concerns. In this work, nonflammable localized high‐concentration electrolytes (LHCEs) are developed for Si‐based anodes. The LHCEs enable the Si anodes with significantly enhanced electrochemical performances comparing to conventional carbonate electrolytes with a high content of fluoroethylene carbonate (FEC). The LHCE with only 1.2 wt% FEC can further improve the long‐term cycling stability of Si‐based anodes. When coupled with a LiNi_0.3Mn_0.3Co_0.3O₂ cathode, the full cells using this nonflammable LHCE can maintain >90% capacity after 600 cycles at C/2 rate, demonstrating excellent rate capability and cycling stability at elevated temperatures and high loadings. This work casts new insights in electrolyte development from the perspective of in situ Si/electrolyte interphase protection for high energy‐density LIBs with Si anodes.     

High‐Performance Flexible Solid‐State Ni/Fe Battery Consisting of Metal Oxides Coated Carbon Cloth/Carbon Nanofiber Electrodes

Aqueous Ni/Fe batteries have great potential as flexible energy storage devices, owing to their low cost, low toxicity, high safety, and high energy density. However, the poor cycling stability has limited the widely expected application of Ni/Fe batteries, while the use of heavy metal substrates cannot meet the basic requirement for flexible devices. In this work, a flexible type of solid‐state Ni/Fe batteries with high energy and power densities is rationally developed using needle‐like Fe₃O₄ and flake‐like NiO directly grown on carbon cloth/carbon nanofiber (CC–CF) matrix as the anode and cathode, respectively. The hierarchical CC–CF substrate with high electric conductivity and good flexibility serves as an ideal support for guest active materials of nanocrystalline Fe₃O₄ and NiO, which can effectively buffer the volume change giving rise to good cycling ability. By utilizing a gel electrolyte, a robust and mechanically flexible quasi‐solid‐state Ni/Fe full cell can be assembled. It demonstrates optimal electrochemical performance, such as high energy density (5.2 mWh cm^?3 and 94.5 Wh Kg^?1), high power density (0.64 W cm^?3 and 11.8 KW Kg^?1), together with excellent cycling ability. This work provides an example of solid‐state alkaline battery with high electrochemical performance and mechanical flexibility, holding great potential for future flexible electronic devices.