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.     

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.     

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.     

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.     

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.     

Defect‐Rich Soft Carbon Porous Nanosheets for Fast and High‐Capacity Sodium‐Ion Storage

Soft carbon has attracted tremendous attention as an anode in rocking‐chair batteries owing to its exceptional properties including low‐cost, tunable interlayer distance, and favorable electronic conductivity. However, it fails to exhibit decent performance for sodium‐ion storage owing to difficulties in the formation of sodium intercalation compounds. Here, microporous soft carbon nanosheets are developed via a microwave induced exfoliation strategy from a conventional soft carbon compound obtained by pyrolysis of 3,4,9,10‐perylene tetracarboxylic dianhydride. The micropores and defects at the edges synergistically leads to enhanced kinetics and extra sodium‐ion storage sites, which contribute to the capacity increase from 134 to 232 mAh g^?1 and a superior rate capability of 103 mAh g^?1 at 1000 mA g^?1 for sodium‐ion storage. In addition, the capacitance‐dominated sodium‐ion storage mechanism is identified through the kinetics analysis. The in situ X‐ray diffraction analyses are used to reveal that sodium ions intercalate into graphitic layers for the first time. Furthermore, the as‐prepared nanosheets can also function as an outstanding anode for potassium‐ion storage (reversible capacity of 291 mAh g^?1) and dual‐ion full cell (cell‐level capacity of 61 mAh g^?1 and average working voltage of 4.2 V). These properties represent the potential of soft carbon for achieving high‐energy, high‐rate, and low‐cost energy storage systems.     

Spontaneous Growth of 3D Framework Carbon from Sodium Citrate for High Energy‐ and Power‐Density and Long‐Life Sodium‐Ion Hybrid Capacitors

Carbon sheets with 3D architectures, large graphitic interlayer spacing, and high electrical conductivity are highly expected to be an ideal anode material for sodium‐ion hybrid capacitors (SIHCs). Pursuing a simple synthesis methodology and advancing it from the laboratory to industry is of great importance. In this study, a new approach is presented to prepare 3D framework carbon (3DFC) with the above integrated advantages by a direct calcination of sodium citrate without aid of any additional carbon source, template, or catalyst. The first‐principle calculations verify that the large interlayer spacing and the curvature structure of 3DFC facilitate the sodium ion insertion/extraction. As a consequence, the optimal 3DFC sample exhibits high reversible capacity as well as excellent rate and cycling performance. On this basis, a dual‐carbon SIHC is fabricated by employing 3DFC as battery‐type anode and 3DFC‐derived nanoporous carbon as capacitor‐type cathode. It is able to deliver high energy‐ and power‐density feature as well as outstanding long‐term cycling stability in the potential range of 0–4.0 V. This study may open an avenue for developing high‐performance carbon electrode materials and pushes the practical applications of SIHCs a decisive step forward.     

A Layered Inorganic–Organic Open Framework Material as a 4 V Positive Electrode with High‐Rate Performance for K‐Ion Batteries

K‐ion batteries (KIBs) are promising for large‐scale energy storage owing to various advantages like the high abundance of potassium resources in the Earth's crust, high operational potentials, and high power due to fast diffusion of K⁺ ions. However, to realize the practical application of KIBs, electrode materials are needed with high operational voltage, good capacity, long cycle life, and low‐cost. This work reports a layered open framework material, K₂[(VOHPO₄)₂(C₂O₄)], composited with reduced graphene oxide (rGO) as a 4 V positive electrode material for KIBs. The material is prepared by a simple precipitation reaction at room temperature. The material demonstrates reversible K‐extraction/insertion with conventional carbonate ester KPF₆ solutions; however, with low specific capacity and low Coulombic efficiency. A high discharge capacity of >100 mAh g^?1 with good cycling stability and higher Coulombic efficiency is achieved in a highly concentrated electrolyte, 7 mol kg^?1 of potassium bis(fluorosulfonyl)amide (KFSA) in dimethoxyethane (DME) at 0.1 C rate. Due to the facile migration of K⁺ ions in the framework, the material exhibits excellent rate capability with a discharge capacity of 80 mAh g^?1 at 10 C rate, and a good capacity retention of 67% after 500 cycles at 2 C rate.     

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.     

Mechanism of Na‐Ion Storage in Hard Carbon Anodes Revealed by Heteroatom Doping

Hard carbon is the leading candidate anode for commercialization of Na‐ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short‐range local order resembling graphene within each layer, but complete disorder along the c‐axis between layers. A primary challenge holding back the development of Na‐ion batteries is that a complete understanding of the structure–capacity correlations of Na‐ion storage in hard carbon has remained elusive. This article presents two key discoveries: first, the characteristics of hard carbons structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na‐ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low‐voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. The combined experimental studies and first principles calculations reveal that it is the Na‐ion‐defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low‐potential plateau capacity. The understanding suggests a new design principle of hard carbon anode: more reversibly binding defects and dilated turbostratic domains, given that the specific surface area is maintained low.     

Confined Fe2VO4⊂Nitrogen‐Doped Carbon Nanowires with Internal Void Space for High‐Rate and Ultrastable Potassium‐Ion Storage

Developing low‐cost, high‐capacity, high‐rate, and robust earth‐abundant electrode materials for energy storage is critical for the practical and scalable application of advanced battery technologies. Herein, the first example of synthesizing 1D peapod‐like bimetallic Fe₂VO₄ nanorods confined in N‐doped carbon porous nanowires with internal void space (Fe₂VO₄?NC nanopeapods) as a high‐capacity and stable anode material for potassium‐ion batteries (KIBs) is reported. The peapod‐like Fe₂VO₄?NC nanopeapod heterostructures with interior void space and external carbon shell efficiently prevent the aggregation of the active materials, facilitate fast transportation of electrons and ions, and accommodate volume variation during the cycling process, which substantially boosts the rate and cycling performance of Fe₂VO₄. The Fe₂VO₄?NC electrode exhibits high reversible specific depotassiation capacity of 380 mAh g^?1 at 100 mA g^?1 after 60 cycles and remarkable rate capability as well as long cycling stability with a high capacity of 196 mAh g^?1 at 4 A g^?1 after 2300 cycles. The first‐principles calculations reveal that Fe₂VO₄?NC nanopeapods have high ionic/electronic conductivity characteristics and low diffusion barriers for K⁺‐intercalation. This study opens up new way for investigating high‐capacity metal oxide as high‐rate and robust electrode materials for KIBs.     

Flexible Na/K‐Ion Full Batteries from the Renewable Cotton Cloth–Derived Stable,Low‐Cost,and Binder‐Free Anode and Cathode

Flexible Na/K‐ion batteries (NIBs/KIBs) exhibit great potential applications and have drawn much attention due to the continuous development of flexible electronics. However, there are still many huge challenges, mainly the design and construction of flexible electrodes (cathode and anode) with outstanding electrochemical properties. In this work, a unique approach to prepare flexible electrode is proposed by utilizing the commercially available cotton cloth–derived carbon cloth (CC) as a flexible anode and the substrate of a cathode. The binder‐free, self‐supporting, and flexible cathodes (FCC@N/KPB) are prepared by growing Prussian blue microcubes on the flexible CC (FCC). Na/K‐ion full batteries (FCC//FCC@N/KPB) are assembled by using FCC and FCC@N/KPB as anode and cathode, respectively. Electrochemical performance, mechanical flexibility, and practicability of FCC//FCC@N/KPB Na/K‐ion full batteries are evaluated in both coin cells and flexible pouch cells, demonstrating their superior energy‐storage properties (excellent rate performance and cycling stability) and remarkable flexibility (they can work under different bending states). This work provides a new and profound strategy to design flexible electrodes, promoting the development of flexible NIBs/KIBs to be practical and sustainable.     

Graphitic Carbon Nanocage as a Stable and High Power Anode for Potassium‐Ion Batteries

As an emerging electrochemical energy storage device, potassium‐ion batteries (PIBs) have drawn growing interest due to the resource‐abundance and low cost of potassium. Graphite‐based materials, as the most common anodes for commercial Li‐ion batteries, have a very low capacity when used an anode for Na‐ion batteries, but they show reasonable capacities as anodes for PIBs. The practical application of graphitic materials in PIBs suffers from poor cyclability, however, due to the large interlayer expansion/shrinkage caused by the intercalation/deintercalation of potassium ions. Here, a highly graphitic carbon nanocage (CNC) is reported as a PIBs anode, which exhibits excellent cyclability and superior depotassiation capacity of 175 mAh g^?1 at 35 C. The potassium storage mechanism in CNC is revealed by cyclic voltammetry as due to redox reactions (intercalation/deintercalation) and double‐layer capacitance (surface adsorption/desorption). The present results give new insights into structural design for graphitic anode materials in PIBs and understanding the double‐layer capacitance effect in alkali metal ion batteries.     

Disordered,Large Interlayer Spacing,and Oxygen‐Rich Carbon Nanosheets for Potassium Ion Hybrid Capacitor

Potassium ion storage technology as a promising substitute for the well‐developed lithium ion storage technology is still at the infancy stage of development, and exploring suitable electrode materials is critical for its practical application. Here, the great feasibility of disordered, large interlayer spacing, and oxygen‐rich carbon nanosheets (CNSs) prepared by chemical vapor deposition for potassium ion storage applications is demonstrated. As an anode material, the CNSs exhibit outstanding rate capability as well as excellent cyclic stability. Taking advantage of this, a potassium ion hybrid capacitor (PIHC) is constructed by employing such CNSs as the battery‐type anode and activated carbon as the capacitor‐type cathode. The resulting device displays a high energy density of 149 Wh kg^?1, an ultrahigh power output of 21 kW kg^?1, as well as a long cycling life (80% capacity retention after 5000 cycles), which are all close to the state‐of‐the‐art values for PIHCs. This work promotes the development of high‐performance anode material for potassium ion storage devices, and the designed PIHC pushes the energy density and power density to a higher level.     

Fast Redox Kinetics in Bi‐Heteroatom Doped 3D Porous Carbon Nanosheets for High‐Performance Hybrid Potassium‐Ion Battery Capacitors

Potassium‐ion hybrid capacitors (PIHCs) hold the advantages of high‐energy density of batteries and high‐power output of supercapacitors and thus present great promise for the next generation of electrochemical energy storage devices. One of the most crucial tasks for developing a high‐performance PIHCs is to explore a favorable anode material with capability to balance the kinetics mismatch between battery‐type anodes and capacitor‐type cathode. Herein, a reliable route for fabricating sulfur and nitrogen codoped 3D porous carbon nanosheets (S‐N‐PCNs) is reported. Systematic characterizations coupled with kinetics analysis indicate that the doped heteroatoms of sulfur and nitrogen and the amplified graphite interlayer can provide ample structural defects and redox active sites that are beneficial for improving pseudocapacitive activity, enabling fast kinetics toward efficient potassium‐ion storage. The S‐N‐PCNs are demonstrated to exhibit superior potassium storage capability with a high capacity of 107 mAh g^?1 at 20 A g^?1 and long cycle stability. The as‐developed PIHCs present impressive electrochemical performance with an operating voltage as high as 4.0 V, an energy density of 187 Wh kg^?1, a power density of 5136 W kg^?1, and a capacity retention of 86.4% after 3000 cycles.     

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.     

Low‐Defect and Low‐Porosity Hard Carbon with High Coulombic Efficiency and High Capacity for Practical Sodium Ion Battery Anode

Hard carbon is regarded as the most promising anode material for commercialization of Na ion batteries because of its high capacity and low cost. At present, the practical utilization of hard carbon anodes is largely limited by the low initial Coulombic efficiency (ICE). Na ions have been found to adopt an adsorption–insertion storage mechanism. In this paper a systematic way to control the defect concentration and porosity of hard carbon with similar overall architectures is shown. This study elucidates that the defects in the graphite layers are directly related to the ICE as they would trap Na ions and create a repulsive electric field for other Na ions so as to shorten the low‐voltage intercalation capacity. The obtained low defect and porosity hard carbon electrode has achieved the highest ICE of 86.1% (94.5% for pure hard carbon material by subtracting that of the conductive carbon black), reversible capacity of 361 mA h g^?1, and excellent cycle stability (93.4% of capacity retention over 100 cycles). This result sheds light on feasible design principles for high performance Na storage hard carbon: suitable carbon layer distance and defect free graphitic layers.     

In Situ Mechanistic Elucidation of Superior Si‐C‐Graphite Li‐Ion Battery Anode Formation with Thermal Safety Aspects

A composite anode material synthesized using silicon nanoparticles, micrometer sized graphite particles, and starch‐derived amorphous carbon (GCSi) offers scalability and enhanced electrochemical performance when compared to existing graphite anodes. Mechanistic elucidation of the formation steps of tailored GCSi composite are achieved with environmental transmission electron microscopy (ETEM) and thermal safety aspects of the composite anode are studied for the first time using specially designed multimode calorimetry for coin cell studies. Electrochemical analysis of the composite anode demonstrates a high initial discharge capacity (1126 mAh g^?1) and yields a high coulombic efficiency of 83% in the first charge cycle. Applying a current density of 500 mA g^?1, the anode composite retains 448 mAh g^?1 specific capacity after 100 cycles. Cycling stability is a result of improved interfacial binding made possible by the interconnected architecture of wheat derived amorphous carbon, enhancing the electrochemical kinetics and decreasing the inherent issues associated with volume expansion and pulverization of pristine Si electrodes. Comparing the energy released during thermal runaway, per specific capacity for the full‐cell, the GCSi composite releases less heat than the conventional graphitic anode, suggesting a synergistic effect of each ingredient of the GCSi composite, providing a safer and higher performing anode.     

Artificial Solid‐Electrolyte Interphase Enabled High‐Capacity and Stable Cycling Potassium Metal Batteries

Secondary batteries based on earth‐abundant potassium metal anodes are attractive for stationary energy storage. However, suppressing the formation of potassium metal dendrites during cycling is pivotal in the development of future potassium metal‐based battery technology. Herein, a promising artificial solid‐electrolyte interphase (ASEI) design, simply covering a carbon nanotube (CNT) film on the surface of a potassium metal anode, is demonstrated. The results show that the spontaneously potassiated CNT framework with a stable self‐formed solid‐electrolyte interphase layer integrates a quasi‐hosting feature with fast interfacial ion transport, which enables dendrite‐free deposition of potassium at an ultrahigh capacity (20 mAh cm^?2). Remarkably, the potassium metal anode exhibits an unprecedented cycle life (over 1000 cycles, over 2000 h) at a high current density of 5 mA cm^?2 and a desirable areal capacity of 4 mAh cm^?2. Dendrite‐free morphology in carbon‐fiber and carbon‐black‐based ASEI for potassium metal anodes, which indicates a broader promise of this approach, is also observed.     

Boosting Fast Sodium Storage of a Large‐Scalable Carbon Anode with an Ultralong Cycle Life

Sodium‐ion batteries (SIBs) are considered to be a promising alternative for large‐scale electricity storage. However, it is urgent to develop new anode materials with superior ultralong cycle life performance at high current rates. Herein, a low‐cost and large‐scalable sulfur‐doped carbon anode material that exhibits the best high‐rate cycle performance and the longest cycle life ever reported for carbon anodes is developed. The material delivers a reversible capacity of 142 mA h g^?1 at a current rate up to 10 A g^?1. After 10 000 cycles the capacity is remained at 126.5 mA h g^?1; 89.1% of the initial value. Density functional theory computations demonstrate that the sulfur‐doped carbon has a strong binding affinity for sodium which promotes sodium storage. Meanwhile, the kinetics analysis identifies the capacitive charge storage as a large contributor to sodium storage, which favors ultrafast storage of sodium ions. These results demonstrate a new way to design carbon‐based SIBs anodes for next‐generation large‐scale electricity storage.