Self‐Healing Materials for Energy‐Storage Devices

The booming development of electronics, electric vehicles, and grid storage stations has led to a high demand for advanced energy‐storage devices (ESDs) and accompanied attention to their reliability under various circumstances. Self‐healing is the ability of an organism to repair damage and restore function through its own internal vitality. Inspired by this, brilliant designs have emerged in recent years using self‐healing materials to significantly improve the lifespan, durability, and safety of ESDs. Extrinsic and intrinsic self‐healing materials and their working principles are first introduced. Then, the application of self‐healing materials in ESDs according to their self‐healing chemistry, including hydrogen bonds, electrostatic interactions, and borate ester bonds, are described in detail. Based on these, critical challenges and important future directions of self‐healing ESDs are discussed.     

Excellent Cycling Stability of Sodium Anode Enabled by a Stable Solid Electrolyte Interphase Formed in Ether‐Based Electrolytes

Sodium‐ion batteries have been considered one of the most promising power sources beyond Li‐ion batteries. Although the Na metal anode exhibits a high theoretical capacity of 1165 mAh g^?1, its application in Na batteries is largely hindered by dendrite growth and low coulombic efficiency. Herein, it is demonstrated that an electrolyte consisting of 1 m sodium tetrafluoroborate in tetraglyme can enable excellent cycling efficiency (99.9%) of a Na metal anode for more than 1000 cycles. This high reversibility of a Na anode can be attributed to a stable solid electrolyte interphase formed on the Na surface, as revealed by cryogenic transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS). These electrolytes also enable excellent cycling stability of Na||hard‐carbon cells and Na||Na_2/3Co_1/3Mn_2/3O₂ cells at high rates with very high coulombic efficiencies.     

3D Carbon Nanotube Network Bridged Hetero‐Structured Ni‐Fe‐S Nanocubes toward High‐Performance Lithium,Sodium, and Potassium Storage

Lithium‐ion, sodium‐ion, and potassium‐ion batteries have captured tremendous attention in power supplies for various electric vehicles and portable electronic devices. However, their practical applications are severely limited by factors such as poor rate capability, fast capacity decay, sluggish charge storage dynamics, and low reversibility. Herein, hetero‐structured bimetallic sulfide (NiS/FeS) encapsulated in N‐doped porous carbon cubes interconnected with CNTs (Ni‐Fe‐S‐CNT) are prepared through a convenient co‐precipitation and post‐heat treatment sulfurization technique of the corresponding Prussian‐blue analogue nanocage precursor. This special 3D hierarchical structure can offer a stable interconnect and conductive network and shorten the diffusion path of ions, thereby greatly enhancing the mobility efficiency of alkali (Li, Na, K) ions in electrode materials. The Ni‐Fe‐S‐CNT nanocomposite maintains a charge capacity of 1535 mAh g^?1 at 0.2 A g^?1 for lithium ion batteries, 431 mAh g^?1 at 0.1 A g^?1 for sodium ion batteries, and 181 mAh g^?1 at 0.1 A g^?1 for potassium‐ion batteries, respectively. The high performance is mainly attributed to the 3D hierarchically high‐conductivity network architecture, in which the hetero‐structured FeS/NiS nanocubes provide fast Li⁺/Na⁺/K⁺ insertion/extraction and reduced ion diffusion paths, and the distinctive 3D networks maintain the electrical contact and guarantee the structural integrity.     

Understanding the Charge Storage Mechanism to Achieve High Capacity and Fast Ion Storage in Sodium‐Ion Capacitor Anodes by Using Electrospun Nitrogen‐Doped Carbon Fibers

Microporous nitrogen‐rich carbon fibers (HAT‐CNFs) are produced by electrospinning a mixture of hexaazatriphenylene‐hexacarbonitrile (HAT‐CN) and polyvinylpyrrolidone and subsequent thermal condensation. Bonding motives, electronic structure, content of nitrogen heteroatoms, porosity, and degree of carbon stacking can be controlled by the condensation temperature due to the use of the HAT‐CN with predefined nitrogen binding motives. The HAT‐CNFs show remarkable reversible capacities (395 mAh g^?1 at 0.1 A g^?1) and rate capabilities (106 mAh g^?1 at 10 A g^?1) as an anode material for sodium storage, resulting from the abundant heteroatoms, enhanced electrical conductivity, and rapid charge carrier transport in the nanoporous structure of the 1D fibers. HAT‐CNFs also serve as a series of model compounds for the investigation of the contribution of sodium storage by intercalation and reversible binding on nitrogen sites at different rates. There is an increasing contribution of intercalation to the charge storage with increasing condensation temperature which becomes less active at high rates. A hybrid sodium‐ion capacitor full cell combining HAT‐CNF as the anode and salt‐templated porous carbon as the cathode provides remarkable performance in the voltage range of 0.5–4.0 V (95 Wh kg^?1 at 0.19 kW kg^?1 and 18 Wh kg^?1 at 13 kW kg^?1).     

Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard‐Carbon Electrodes and Application to Na‐Ion Batteries

Recently, lithium‐ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confirmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the first practical application in 1991 to the present and is increasing due to global demand for lithium‐ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium‐free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium‐insertion performance of hard‐carbon and layered NaNi_0.5Mn_0.5O₂ electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard‐carbon are investigated to study the reversible sodium insertion. The 3‐volt secondary Na‐ion battery possessing environmental and cost friendliness, Na⁺‐shuttlecock hard‐carbon/NaNi_0.5Mn_0.5O₂ cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li‐ion batteries.     

N‐Doping and Defective Nanographitic Domain Coupled Hard Carbon Nanoshells for High Performance Lithium/Sodium Storage

Hard carbons (HCs) possess high lithium/sodium storage capacities, which however suffer from low electric conductivity and poor ion diffusion kinetics. An efficient structure design with appropriate heteroatoms doping and optimized graphitic/defective degree is highly desired to tackle these problems. This work reports a new design of N‐doped HC nanoshells (N‐GCNs) with homogeneous defective nanographite domains, fabricated through the prechelation between Ni²⁺ and chitosan and subsequent catalyst confined graphitization. The as‐prepared N‐GCNs deliver a high reversible lithium storage capacity of 1253 mA h g^?1, with outstanding rate performance (175 mA h g^?1 at a high rate of 20 A g^?1) and good cycling stability, which outperforms most state‐of‐the‐art HCs. Meanwhile, a high reversible sodium storage capacity of 325 mA h g^?1 is also obtained, which stabilizes at 174 mA h g^?1 after 200 cycles. Density functional theory calculations are performed to uncover the coupling effect between heteroatom‐doping and the defective nanographitic domains down to the atomic scale. The in situ Raman analysis reveals the “adsorption mechanism” for sodium storage and the “adsorption–intercalation mechanism” for lithium storage of N‐GCNs.     

Enhanced Capacitive Energy Storage in Polyoxometalate‐Doped Polypyrrole

High‐performance batteries and supercapacitors require the molecular‐level linkage of charge transport components and charge storage components. This study shows how redox‐tunable Lindqvist‐type molecular metal oxide anions [V_nM _6–n O₁₉]^{(2+n )?} (M = W(VI) or Mo(VI); n = 0, 1, 2) can be incorporated in cationic polypyrrole (PPy) conductive polymer films by means of electrochemical polymerization. Electron microscopy and (spectro‐)electrochemistry show that the electroactivity and morphology of the composites can be tuned by Lindqvist anion incorporation. Reductive electrochemical “activation” of the Lindqvist–PPy composites leads to significantly increased electrical capacitance (range: ≈25–38 F g^?1, increase up to ≈25×), highlighting that this general synthetic route gives access to promising capacitive materials with suitable long‐term stability. Electrochemical, electron microscopic, and Raman spectroscopic analyses together with density functional theory (DFT) calculations provide molecular‐level insight into the effects of Lindqvist anion incorporation in PPy films and their role during reductive activation. The study therefore provides fundamental understanding of the principles governing the bottom‐up integration of molecular components into nanostructured composites for electrochemical energy storage.     

Self‐Supported 3D Array Electrodes for Sodium Microbatteries

The ever‐increasing demand for autonomous microelectronic devices necessitates on‐chip miniature energy storage systems such as microbatteries. Conventional microbatteries adopt planar thin‐film electrodes that display limited areal energy and power due to their undesired coupling. To achieve high energy and power simultaneously, employment of 3D array electrodes has proven indispensable. Adoption of 3D electrodes has become a fashionable trend in lithium microbatteries during the last decade. This trend also occurs in sodium batteries, which are an important alternative to the current lithium system owing to the potentially high power and wide availability of sodium. In this perspective, state‐of‐the‐art progress in design and application of 3D arrays for sodium microbatteries are summarized. Specifically, emphasis is placed on material strategies to efficiently address the intrinsic limitations of pristine arrays such as transportation, activity, and stability. Future challenges and prospects in this field are also discussed, and the importance of integrating novel concepts into 3D electrode fabrication, characterization, and modeling to meet practical requirements is highlighted.     

Wood‐Derived Lightweight and Elastic Carbon Aerogel for Pressure Sensing and Energy Storage

Lightweight and elastic carbon materials have attracted great interest in pressure sensing and energy storage for wearable devices and electronic skins. Wood is the most abundant renewable resource and offers green and sustainable raw materials for fabricating lightweight carbon materials. Herein, a facile and sustainable strategy is proposed to fabricate a wood‐derived elastic carbon aerogel with tracheid‐like texture from cellulose nanofibers (CNFs) and lignin. The flexible CNFs entangle and assemble into an interconnected framework, while lignin with high thermal stability and favorable stiffness prevents the framework from severe structural shrinkage during annealing. This strategy leads to an ordered tracheid‐like structure and significantly reduces the thermal deformation of the CNFs network, producing a lightweight and elastic carbon aerogel. The wood‐derived carbon aerogel exhibits excellent mechanical performance, including high compressibility (up to 95% strain) and fatigue resistance. It also reveals high sensitivity at a wide working pressure range of 0–16.89 kPa and can detect human biosignals accurately. Moreover, the carbon aerogel can be assembled into a flexible and free‐standing all‐solid‐state symmetric supercapacitor that reveals satisfactory electrochemical performance and mechanical flexibility. These features make the wood‐derived carbon aerogel highly attractive for pressure sensor and flexible electrode applications.     

Surface‐Driven Energy Storage Behavior of Dual‐Heteroatoms Functionalized Carbon Material

Heteroatom modification represents one of the major areas of carbon materials' research in electrical energy storage. However, the influence of heteroatomic state evolution on electrochemical properties remains an elusive topic. Herein, thiophene‐2,5‐dicarboxylic acid is chemically activated to prepare O,S‐diatomic hybrid carbon material (OS–C). The heteroatoms and carbon matrix coexist in the form of C?O/C? O and C? S/S? S bonds, which introduce porous networks to the partially graphitized carbon skeleton and provide abundant active sites for better ion absorption. Moreover, the heteroatoms and carbon matrix are bridged to establish stable pseudocapacitive functional groups like quinoid unit and disulfide bonds, which can be electrochemically converted into benzenoid units and mercaptan anions through Faradaic reactions to further improve the reversible capacity. Combined with the detailed kinetic exploration and in situ investigation of the electrochemical impedance spectra, the energy storage mechanism for lithium/sodium is proposed in the following steps: Faradaic reactions at a higher potential range, energy storage at active sites, and ions intercalation on the graphitized parts in the low‐voltage states. Greatly, the electrode can store lithium up to the capacity of ≈700 mAh g^?1, while also delivering ≈330 mAh g^?1 of sodium storage, providing lifetimes in excess of thousands of cycles.     

Prolifera‐Green‐Tide as Sustainable Source for Carbonaceous Aerogels with Hierarchical Pore to Achieve Multiple Energy Storage

The increasing demand for efficient energy storage and conversion devices has aroused great interest in designing advanced materials with high specific surface areas, multiple holes, and good conductivity. Here, we report a new method for fabricating a hierarchical porous carbonaceous aerogel (HPCA) from renewable seaweed aerogel. The HPCA possesses high specific surface area of 2200 m² g^?1 and multilevel micro/meso/macropore structures. These important features make HPCA exhibit a reversible lithium storage capacity of 827.1 mAh g^?1 at the current density of 0.1 A g^?1, which is the highest capacity for all the previously reported nonheteroatom‐doped carbon nanomaterials. It also shows high specific capacitance and excellent rate performance for electric double layer capacitors (260.6 F g^?1 at 1 A g^?1 and 190.0 F g^?1 at 50 A g^?1), and long cycle life with 91.7% capacitance retention after 10 000 cycles at 10 A g^?1. The HPCA also can be used as support to assemble Co₃O₄ nanowires (Co₃O₄@HPCA) for constructing a high performance pseudocapacitor with the maximum specific capacitance of 1167.6 F g^?1 at the current density of 1 A g^?1. The present work highlights the first example in using prolifera‐green‐tide as a sustainable source for developing advanced carbon porous aerogels to achieve multiple energy storage.     

Polyanion Sodium Vanadium Phosphate for Next Generation of Sodium‐Ion Batteries—A Review

Polyanion‐type sodium (Na) vanadium phosphate in the form of Na₃V₂(PO₄)₃ has demonstrated reasonably high capacity, good rate capability, and excellent cyclability. Two of three Na ions per formula can be deintercalated at a potential 3.4 V versus Na⁺/Na with oxidation of V^3+/4+. In the reversible process, two Na ions intercalate back resulting in a discharge capacity of 117.6 mAh g^?1. Further intercalation is possible but at a low potential of 1.4 V versus Na⁺/Na accompanied by vanadium reduction V^3+/2+, leading to a capacity of 60 mAh g^?1. Due to its marvelous electrochemical performance, it has attracted a lot of attention since its discovery in the 1990s. To develop truly useable polyanion‐type vanadium phosphate, better understanding of its crystal configuration, sodium ions' transportation, and electronic structure is essential. Therefore, this review only focuses on the inside of crystal configuration and electronic structure of polyanion‐type vanadium phosphate, Na₃V₂(PO₄)₃, since there are a few good reviews on various processing technologies.     

A Structurable Gel‐Polymer Electrolyte for Sodium Ion Batteries

In this work, a structurable gel‐polymer electrolyte (SGPE) with a controllable pore structure that is not destroyed after immersion in an electrolyte is produced via a simple nonsolvent induced phase separation (NIPS) method. This study investigates how the regulation of the nonsolvent content affects the evolving nanomorphology of the composite separators and overcomes the drawbacks of conventional separators, such as glass fiber (GF), which has been widely used in sodium ion batteries (SIBs), through the regulation of pore size and gel‐polymer position. The interfacial resistance is reduced through selective positioning of a poly(vinylidene fluoride‐co‐hexa fluoropropylene) (PVdF‐HFP) gel‐polymer with the aid of NIPS, which in turn enhances the compatibility between the electrolyte and electrode. In addition, the highly porous morphology of the GF/SGPE obtained via NIPS allows for the absorption of more liquid electrolyte. Thus, a greatly improved cell performance of the SIBs is observed when a tailored SGPE is incorporated into the GF separator through charge/discharge testing compared with the performance observed with pristine GF and conventional GF coated with PVdF‐HFP gel‐polymer.     

Hard–Soft Carbon Composite Anodes with Synergistic Sodium Storage Performance

A series of hard–soft carbon composite materials is produced from biomass and oil waste and applied as low‐cost anodes for sodium‐ion batteries to study the fundamentals behind the dependence of Na storage on their structural features. A good reversible capacity of 282 mAh g^?1 is obtained at a current density of 30 mA g^?1 with a high initial Coulombic efficiency of 80% at a carbonization temperature of only 1000 °C by adjusting the ratio of hard to soft carbon. The performance is superior to the pure hard or soft carbon anodes produced at the same temperatures. This synergy between hard and soft carbon resulting in an excellent performance is due to the blockage of some open pores in hard carbon by the soft carbon, which suppresses the solid electrolyte interface formation and increases the reversible sodium storage capacity.     

Ultrathin Nickel–Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under Aqueous/Solid‐State Electrolyte

2D materials are ideal for constructing flexible electrochemical energy storage devices due to their great advantages of flexibility, thinness, and transparency. Here, a simple one‐step hydrothermal process is proposed for the synthesis of nickel–cobalt phosphate 2D nanosheets, and the structural influence on the pseudocapacitive performance of the obtained nickel–cobalt phosphate is investigated via electrochemical measurement. It is found that the ultrathin nickel–cobalt phosphate 2D nanosheets with an Ni/Co ratio of 4:5 show the best electrochemical performance for energy storage, and the maximum specific capacitance up to 1132.5 F g^?1. More importantly, an aqueous and solid‐state flexible electrochemical energy storage device has been assembled. The aqueous device shows a high energy density of 32.5 Wh kg^?1 at a power density of 0.6 kW kg^?1, and the solid‐state device shows a high energy density of 35.8 Wh kg^?1 at a power density of 0.7 kW kg^?1. These excellent performances confirm that the nickel–cobalt phosphate 2D nanosheets are promising materials for applications in electrochemical energy storage devices.     

Development of Vanadium‐Coated Carbon Microspheres: Electrochemical Behavior as Electrodes for Supercapacitors

Vanadium‐coated carbon‐xerogel microspheres are successfully prepared by a specific designed sol–gel method, and their supercapacitor behavior is tested in a two‐electrode system. Nitrogen adsorption shows that these composite materials present a well‐developed micro‐ and mesoporous texture, which depends on the vanadium content in the final composite. A high dispersion of vanadium oxide on the carbon microsphere surface is reached, being the vanadium particle size around 4.5 nm. Moreover, low vanadium oxidation states are stabilized by the carbon matrix in the composites. The complete electrochemical characterization of the composites is carried out using cyclic voltammetry, chronopotentiometry, cycling charge–discharge, and impedance spectroscopy. The results show that these composites present high capacitance as 224 F g^?1, with a high capacitance retention which is explained on the basis of the presence of vanadium oxide, texture, and chemistry surface.     

Local Built‐In Electric Field Enabled in Carbon‐Doped Co3O4 Nanocrystals for Superior Lithium‐Ion Storage

In this work, a novel concept of introducing a local built‐in electric field to facilitate lithium‐ion transport and storage within interstitial carbon (C‐) doped nanoarchitectured Co₃O₄ electrodes for greatly improved lithium‐ion storage properties is demonstrated. The imbalanced charge distribution emerging from the C‐dopant can induce a local electric field, to greatly facilitate charge transfer. Via the mechanism of “surface locking” effect and in situ topotactic conversion, unique sub‐10 nm nanocrystal‐assembled Co₃O₄ hollow nanotubes (HNTs) are formed, exhibiting excellent structural stability. The resulting C‐doped Co₃O₄ HNT‐based electrodes demonstrate an excellent reversible capacity ≈950 mA h g^?1 after 300 cycles at 0.5 A g^?1 and superior rate performance with ≈853 mA h g^?1 at 10 A g^?1.     

Facile Spraying Synthesis and High‐Performance Sodium Storage of Mesoporous MoS2/C Microspheres

A facile one‐step spraying synthesis of MoS₂/C microspheres and their enhanced electrochemical performance as anode of sodium‐ion batteries is reported. An aerosol spraying pyrolysis without any template is employed to synthesize MoS₂/C microspheres, in which ultrathin MoS₂ nanosheets (≈2 nm) with enlarged interlayers (≈0.64 nm) are homogeneously embedded in mesoporous carbon microspheres. The as‐synthesized mesoporous MoS₂/C microspheres with 31 wt% carbon have been applied as an anode material for sodium ion batteries, demonstrating long cycling stability (390 mAh g^?1 after 2500 cycles at 1.0 A g^?1) and high rate capability (312 mAh g^?1 at 10.0 A g^?1 and 244 mAh g^?1 at 20.0 A g^?1). The superior electrochemical performance is due to the uniform distribution of ultrathin MoS₂ nanosheets in mesoporous carbon frameworks. This kind of structure not only effectively improves the electronic and ionic transport through MoS₂/C microspheres, but also minimizes the influence of pulverization and aggregation of MoS₂ nanosheets during repeated sodiation and desodiation.     

Rechargeable Na–SO2 Battery with Ethylenediamine Additive in Ether‐Based Electrolyte

Rechargeable metal–SO₂ batteries have drawn tremendous attention because it can accelerate SO₂ fixation/utilization and offer high energy density. Herein, a rechargeable Na–SO₂ battery based on an ether‐based liquid electrolyte with an ethylenediamine (EDA) additive is realized via the reversible formation/decomposition of Na₂S₂O₄. Experimental investigations reveal that the EDA additive provides three benefits by simultaneously decreasing the overall electrode polarization, increasing the full discharge capacity, and improving battery cyclability. At a current density of 250 mA g^?1, the full discharge capacity of the battery with the EDA additive is more than twice of a similar system in the absence of EDA. In addition to the significantly enhanced capacity, the as‐assembled Na–SO₂ battery demonstrates excellent cyclic stability after 200 cycles, which is equivalent to a total duration of 1600 h. Moreover, the corrosion resistance of Na anode is strengthened with the aid of EDA in the SO₂‐containing liquid electrolyte. This work will pave the way for Na–SO₂ batteries as a promising battery technology toward both pollutant gas utilization and energy storage.