K‐Ion Batteries Based on a P2‐Type K0.6CoO2 Cathode

K‐ion batteries are a potentially exciting and new energy storage technology that can combine high specific energy, cycle life, and good power capability, all while using abundant potassium resources. The discovery of novel cathodes is a critical step toward realizing K‐ion batteries (KIBs). In this work, a layered P2‐type K_0.6CoO₂ cathode is developed and highly reversible K ion intercalation is demonstrated. In situ X‐ray diffraction combined with electrochemical titration reveals that P2‐type K_0.6CoO₂ can store and release a considerable amount of K ions via a topotactic reaction. Despite the large amount of phase transitions as function of K content, the cathode operates highly reversibly and with good rate capability. The practical feasibility of KIBs is further demonstrated by constructing full cells with a graphite anode. This work highlights the potential of KIBs as viable alternatives for Li‐ion and Na‐ion batteries and provides new insights and directions for the development of next‐generation energy storage systems.     

Short‐Range Order in Mesoporous Carbon Boosts Potassium‐Ion Battery Performance

The adequate potassium resource on the earth has driven the researchers to explore new‐concept potassium‐ion batteries (KIBs) with high energy density. Graphite is a common anode for KIBs; however, the main challenge faced by KIBs is that K ions have the larger size than Li and Na ions, hindering the intercalation of K ions into electrodes and thus leading to poor rate performance, low capacity, and cycle stability during the potassiation and depotassiation process. Herein, an amorphous ordered mesoporous carbon (OMC) is reported as a new anode material for high‐performance KIBs. Unlike the well‐crystallized graphite, in which the K ions are squeezed into the restricted interlayer spacing, it is found that the amorphous OMC possesses larger interlayer spacing in short range and fewer carbon atoms in one carbon‐layers cluster, making it more flexible to the deformation of carbon layers. The larger interlayer spacing and the unique layered structure in short range can intercalate more K ions into the carbon layer, accommodate the increase of the interlayer spacing, and tolerate the volume expansion, resulting in a battery behavior with high capacity, high rate capability, and long cycle life.     

Comprehensive New Insights and Perspectives into Ti‐Based Anodes for Next‐Generation Alkaline Metal (Na+, K+) Ion Batteries

Sodium ion batteries (NIBs) and potassium ion batteries (KIBs) are promising candidates for large‐scale energy storage systems, with a similar “rocking chair” working principle to lithium ion batteries due to their earth abundance and lower cost. One of the major challenges in NIB research is the search for suitable anode materials with long lifetimes and high specific capacities. The research on KIBs is still in its infancy. Titanium‐based anodes present low lattice strain, high safety, and overall stability during cycling, which make them promising for large‐scale systems, especially for stationary batteries. In this review, the latest progress on titanium‐based anodes for NIBs and KIBs is summarized, including titanium dioxide and its composite, Na _x TiO₂ systems, NaTi₂(PO₄)₃, titanates, and MXenes. The synthesis methods, modification methods, and sodium or potassium ion storage mechanisms of titanium‐based anodes are detailed; also the current challenges and future opportunities are discussed.     

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.     

A Dual‐Carbon Battery Based on Potassium‐Ion Electrolyte

Although potassium‐ion batteries (KIBs) have been considered to be promising alternatives to conventional lithium‐ion batteries due to large abundance and low cost of potassium resources, their development still stays at the infancy stage due to the lack of appropriate cathode and anode materials with reversible potassium insertion/extraction as well as good rate and cycling performance. Herein, a novel dual‐carbon battery based on a potassium‐ion electrolyte (named as K‐DCB), utilizing expanded graphite as cathode material and mesocarbon microbead as anode material is developed. The working mechanism of the K‐DCB is investigated, which is further demonstrated to deliver a high reversible capacity of 61 mA h g^‐1 at a current density of 1C over a voltage window of 3.0–5.2 V, as well as good cycling performance with negligible capacity decay after 100 cycles. Moreover, the high working voltage with medium discharge voltage of 4.5 V also enables the K‐DCB to meet the requirement of some high‐voltage devices. With the merits of environmental friendliness, low cost and high energy density, the K‐DCB shows attractive potential for future energy storage application.     

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.     

Regulating Pore Structure of Hierarchical Porous Waste Cork‐Derived Hard Carbon Anode for Enhanced Na Storage Performance

Porous structure design is generally considered to be a reliable strategy to boost ion transport and provide active sites for disordered carbon anodes of Na‐ion batteries (NIBs). Herein, a type of waste cork‐derived hard carbon material (CC) is reported for efficient Na storage via tuning the pore species. Benefiting from the natural holey texture of this renewable precursor, CCs deliver a novel hierarchical porous structure. The effective skeletal density test combined with small angle X‐ray scattering analysis (SAXS) is used to obtain the closed pore information. Based on a detailed correlation analysis between pore information and the electrochemical performance of CCs, improving pyrolysis temperature to reduce open pores (related to initial capacity loss) and increase closed pores (related to plateau capacity) endows an optimal CC with a high specific capacity of ≈360 mAh g^?1 in half‐cells and a high energy density of 230 Wh kg^?1 in full‐cells with a capacity retention of 71% after 2000 cycles at 2C rate. The bioinspired high temperature pore‐closing strategy and the new insights about the pore structure–performance relationship provide a rational guide for designing porous carbon anode of NIBs with tailored pore species and high Na storage capacity.     

All‐Manganese‐Based Binder‐Free Stretchable Lithium‐Ion Batteries

Advanced electrode materials with bendability and stretchability are critical for the rapid development of fully flexible/stretchable lithium‐ion batteries. However, the sufficiently stretchable lithium‐ion battery is still underdeveloped that is one of the biggest challenges preventing from realizing fully deformable power sources. Here, a low‐temperature hydrothermal synthesis of a cathode material for stretchable lithium‐ion battery is reported by the in situ growth of LiMn₂O₄ (LMO) nanocrystals inside 3D carbon nanotube (CNT) film networks. The LMO/CNT film composite has demonstrated the chemical bonding between the LMO active materials and CNT scaffolds, which is the most important characteristic of the stretchable electrodes. When coupled with a wrinkled MnO_x /CNT film anode, a binder‐free, all‐manganese‐based stretchable full battery cell is assembled which delivers a high average specific capacity of ≈97 mA h g^?1 and stabilizes after over 300 cycles with an enormous strain of 100%. Furthermore, combining with other merits such as low cost, natural abundance, and environmentally friendly, the all‐manganese design is expected to accelerate the practical applications of stretchable lithium‐ion batteries for fully flexible and biomedical electronics.     

Bismuth Microparticles as Advanced Anodes for Potassium‐Ion Battery

Potassium‐ion batteries (KIBs) are important alternatives to lithium‐ and sodium‐ion batteries. Herein, microsized a Bi electrode delivers exceptional potassium storage capacity, stability, and rate capability by the formation of an elastic and adhesive oligomer‐containing solid electrolyte interface with the assistance of diglyme electrolytes. The kinetics‐controlled K–Bi phase transitions are unraveled combining electrochemical profiles, in situ X‐ray diffraction and density functional theory calculations. Reversible, stepwise Bi–KBi₂–K₃Bi₂–K₃Bi transitions govern the electrochemical processes after the initial continuous surface potassiation. The Bi electrode outperforms the other anode counterparts considering both capacity and potential. This work provides critical insights into the rational design of high‐performance anode materials for KIBs.     

Elucidation of the Sodium‐Storage Mechanism in Hard Carbons

Hard carbons (HCs) are the most promising candidate anode materials for emerging Na‐ion batteries (NIBs). HCs are composed of misaligned graphene sheets with plentiful nanopores and defects, imparting a complex correlation between its structure and sodium‐storage behavior. The currently debated mechanism of Na⁺‐ion insertion in HCs hinders the development of high‐performance NIBs. In this article, ingenious and reliable strategies are used to elaborate the correlation between the structure and electrochemical performance and further illuminate the sodium‐storage mechanism in HCs. First, filling sulfur into the micropores of HCs can remove the low‐voltage plateau, providing solid evidence for its association with the pore‐filling mechanism. Along with the decreased concentration of defects/heteroatoms at higher treatment temperature, the reduced sloping capacity confirms the adsorption mechanism in the sloping region. Finally, the similar sodium‐insertion behaviors of HCs with ether‐based and ester‐based electrolytes indicate that no Na⁺ ions intercalate between the graphene layers. The determined adsorption‐pore‐filling mechanism encourages the design of more efficient HC anode materials with high capacity for high‐energy NIBs.     

Sulfur/Oxygen Codoped Porous Hard Carbon Microspheres for High‐Performance Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are very promising alternatives to lithium‐ion batteries (LIBs) for large‐scale energy storage. However, traditional carbon anode materials usually show poor performance in KIBs due to the large size of K ions. Herein, a carbonization‐etching strategy is reported for making a class of sulfur (S) and oxygen (O) codoped porous hard carbon microspheres (PCMs) material as a novel anode for KIBs through pyrolysis of the polymer microspheres (PMs) composed of a liquid crystal/epoxy monomer/thiol hardener system. The as‐made PCMs possess a porous architecture with a large Brunauer–Emmett–Teller surface area (983.2 m² g^?1), an enlarged interlayer distance (0.393 nm), structural defects induced by the S/O codoping and also amorphous carbon nature. These new features are important for boosting potassium ion storage, allowing the PCMs to deliver a high potassiation capacity of 226.6 mA h g^?1 at 50 mA g^?1 over 100 cycles and be displaying high stability by showing a potassiation capacity of 108.4 mA h g^?1 over 2000 cycles at 1000 mA g^?1. The density functional theory calculations demonstrate that S/O codoping not only favors the adsorption of K to the PCMs electrode but also reduces its structural deformation during the potassiation/depotassiation. The present work highlights the important role of hierarchical porosity and S/O codoping in potassium storage.     

An Organic Anode for High Temperature Potassium‐Ion Batteries

The wide applications of rechargeable batteries require state‐of‐the‐art batteries that are sustainable (abundant resource), tolerant to high‐temperature operations, and excellent in delivering high capacity and long‐term cycling life. Due to the scarcity and uneven distribution of lithium, it is urgent to develop alternative rechargeable batteries. Herein, an organic compound, azobenzene‐4,4′‐dicarboxylic acid potassium salts (ADAPTS) is developed, with an azo group as the redox center for high performance potassium‐ion batteries (KIBs). The extended π‐conjugated structure in ADAPTS and surface reactions between ADAPTS and K‐ions enable the stable charge/discharge of K‐ion batteries even at high temperatures up to 60 °C. When operated at 50 °C, ADAPTS anode delivers a reversible capacity of 109 mAh g^?1 at 1C for 400 cycles. A reversible capacity of 77 mAh g^?1 is retained at 2C for 1000 cycles. At 60 °C, the ADAPTS‐based KIBs deliver a high capacity of 113 mAh g^?1 with 81% capacity retention at 2C after 80 cycles. The exceptional electrochemical performance demonstrates that ADAPTS is a promising electrode material for high‐temperature KIBs.     

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.     

Self‐Supported Tin Sulfide Porous Films for Flexible Aluminum‐Ion Batteries

High‐performance flexible batteries are promising energy storage devices for portable and wearable electronics. Currently, the major obstacle to develop flexible batteries is the shortage of flexible electrodes with excellent electrochemical performance. Another challenge is the limited progress in the flexible batteries beyond Li‐ion because of a safety concern for the Li‐based electrochemical system. In this work, a self‐supported tin sulfide (SnS) porous film (PF) is fabricated as a flexible cathode material in an Al‐ion battery, which delivers a high specific capacity of 406 mAh g^?1. A capacity decay rate of 0.03% per cycle is achieved, indicating a good stability. The self‐supported and flexible SnS film also shows an outstanding electrochemical performance and stability during dynamic and static bending tests. In situ transmission electron microscopy demonstrates that the porous structure of SnS is beneficial for minimizing the volume expansion during charge/discharge. This leads to an improved structural stability and superior long‐term cyclability.     

A Practicable Li/Na‐Ion Hybrid Full Battery Assembled by a High‐Voltage Cathode and Commercial Graphite Anode: Superior Energy Storage Performance and Working Mechanism

With the rapidly growing demand for low‐cost and safe energy storage, the advanced battery concepts have triggered strong interests beyond the state‐of‐the‐art Li‐ion batteries (LIBs). Herein, a novel hybrid Li/Na‐ion full battery (HLNIB) composed of the high‐energy and lithium‐free Na₃V₂(PO₄)₂O₂F (NVPOF) cathode and commercial graphite anode mesophase carbon micro beads is for the first time designed. The assembled HLNIBs exhibit two high working voltage at about 4.05 and 3.69 V with a specific capacity of 112.7 mA h g^?1. Its energy density can reach up to 328 W h kg^?1 calculated from the total mass of both cathode and anode materials. Moreover, the HLNIBs show outstanding high‐rate capability, long‐term cycle life, and excellent low‐temperature performance. In addition, the reaction kinetics and Li/Na‐insertion/extraction mechanism into/out NVPOF is preliminarily investigated by the galvanostatic intermittent titration technique and ex situ X‐ray diffraction. This work provides a new and profound direction to develop advanced hybrid batteries.     

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm^?2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm^?3 at 77.5 mA cm^?3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes.     

All‐Nanomat Lithium‐Ion Batteries: A New Cell Architecture Platform for Ultrahigh Energy Density and Mechanical Flexibility

The ongoing surge in demand for high‐energy/flexible rechargeable batteries relentlessly drives technological innovations in cell architecture as well as electrochemically active materials. Here, a new class of all‐nanomat lithium‐ion batteries (LIBs) based on 1D building element‐interweaved heteronanomat skeletons is demonstrated. Among various electrode materials, silicon (Si, for anode) and overlithiated layered oxide (OLO, for cathode) materials are chosen as model systems to explore feasibility of this new cell architecture and achieve unprecedented cell capacity. Nanomat electrodes, which are completely different from conventional slurry‐cast electrodes, are fabricated through concurrent electrospinning (for polymeric nanofibers) and electrospraying (for electrode materials/carbon nanotubes (CNTs)). Si (or rambutan‐shaped OLO/CNT composite) powders are compactly embedded in the spatially interweaved polymeric nanofiber/CNT heteromat skeletons that play a crucial role in constructing 3D‐bicontinuous ion/electron transport pathways and allow for removal of metallic foil current collectors. The nanomat Si anodes and nanomat OLO cathodes are assembled with nanomat Al₂O₃ separators, leading to the fabrication of all‐nanomat LIB full cells. Driven by the aforementioned structural/chemical uniqueness, the all‐nanomat full cell shows exceptional improvement in electrochemical performance (notably, cell‐based gravimetric energy density = 479 W h kg_Cell^?1) and also mechanical deformability, which lie far beyond those achievable with conventional LIB technologies.     

Electrochemical Performance of Porous Carbon/Tin Composite Anodes for Sodium‐Ion and Lithium‐Ion Batteries

The electrochemical performance of mesoporous carbon (C)/tin (Sn) anodes in Na‐ion and Li‐ion batteries is systematically investigated. The mesoporous C/Sn anodes in a Na‐ion battery shows similar cycling stability but lower capacity and poorer rate capability than that in a Li‐ion battery. The desodiation potentials of Sn anodes are approximately 0.21 V lower than delithiation potentials. The low capacity and poor rate capability of C/Sn anode in Na‐ion batteries is mainly due to the large Na‐ion size, resulting in slow Na‐ion diffusion and large volume change of porous C/Sn composite anode during alloy/dealloy reactions. Understanding of the reaction mechanism between Sn and Na ions will provide insight towards exploring and designing new alloy‐based anode materials for Na‐ion batteries.     

Sodium Vanadium Fluorophosphates (NVOPF) Array Cathode Designed for High‐Rate Full Sodium Ion Storage Device

3D batteries continue to be of widespread interest for flexible energy storage where the 3D nanostructured cathode is the key component to achieve both high energy and power densities. While current work on flexible cathodes tends to emphasize the use of flexible scaffolds such as graphene and/or carbon nanotubes, this approach is often limited by poor electrical contact and structural stability. This communication presents a novel synthetic approach to form 3D array cathode for the first time, the single‐crystalline Na₃(VO)₂(PO₄)₂F (NVOPF) by using VO₂ array as a seed layer. The NVOPF cathode exhibits both high‐rate capability (charge/discharge in 60 s) and long‐term durability (10,000 cycles at 50 C) for Na ion storage. Utilizing in situ X‐ray diffraction and first principles calculations, the high‐rate properties are correlated with the small volume change, 2D fast ion transport, and the array morphology. A novel all‐array flexible Na⁺ hybrid energy storage device based on pairing the intercalation‐type NVOPF array cathode with a cogenetic pseudocapacitive VO₂ nanosheet array anode is demonstrated.     

Unlocking Few‐Layered Ternary Chalcogenides for High‐Performance Potassium‐Ion Storage

Potassium‐ion batteries (KIBs) have attracted increasing attention for grid‐scale energy storage due to the abundance of potassium resources, low cost, and competitive energy density. The key challenge for KIBs is to develop high‐performance electrode materials. However, the exploration of high‐capacity and ultrastable electrodes for KIBs remains challenging because of the sluggish diffusion kinetics of K⁺ ions during the charging/discharging processes. This study reports for the first time a facile ion‐intercalation‐mediated exfoliation method with Mg²⁺ cations and NO₃^– anions as ion assistants for the fabrication of expanded few‐layered ternary Ta₂NiSe₅ (EF‐TNS) flakes with interlayer spacing up to 1.1 nm and abundant Se sites (NiSe₄ tetrahedra/TaSe₆ octahedra clusters) for superior potassium‐ion storage. The EF‐TNS deliver a high capacity of 315 mAh g^–1, excellent rate capability (121 mAh g^–1 at a current density of 1000 mA g^–1), and ultrastable cycling performance (81.4% capacity retention after 1100 cycles). Detailed theoretical analysis via first‐principles calculations and experimental results elucidate that K⁺ ions intercalate through the expanded interlayers effectively and prefer to transport along zigzag pathways in layered Ta₂NiSe₅. This work provides a new avenue for designing novel ternary intercalation/pseudocapacitance‐type KIBs with high capacity, excellent rate capability, and superior long‐term cycling performance.