The Features and Progress of Electrolyte for Potassium Ion Batteries

In Situ Defect Engineering in Carbon by Atomic Self-Activation to Boost the Accessible Low-Voltage Insertion for Advanced Potassium-Ion Full-Cells

Enhancing the low-potential capacity of anode materials is significant in boosting the operating voltage of full-cells and constructing high energy-density energy storage devices. Graphitic carbons exhibit outstanding low-potential potassium storage performance, but show a low K+ diffusion kinetics. Herein, in situ defect engineering in graphitic nanocarbon is achieved by an atomic self-activation strategy to boost the accessible low-voltage insertion. Graphitic carbon layers grow on nanoscale-nickel to form the graphitic nanosphere with short-range ordered microcrystalline due to nickel graphitization catalyst. Meanwhile, the widely distributed K+ in the precursor induces the activation of surrounding carbon atoms to in situ generate carbon vacancies as channels. The graphite microcrystals with defect channels realize reversible K+ intercalation at low-potential and accessible ion diffusion kinetics, contributing to high reversible capacity (209 mAh g-1 at 0.05 A g-1 under 0.8 V) and rate capacity (103.2 mAh g-1 at 1 A g-1). The full-cell with Prussian blue cathode and graphitic nanocarbon anode maintains an obvious working platform at ca. 3.0 V. This work provides a strategy for the in situ design of carbon anode materials and gives insights into the potassium storage mechanism at low-potential for high-performance full-cells.

Restructuring Electrolyte Solvation by a Partially and Weakly Solvating Cosolvent toward High-Performance Potassium-Ion Batteries

Ether-based electrolytes are among the most important electrolytes for potassium-ion batteries (PIBs) due to their low polarization voltage and notable compatibility with potassium metal. However, their development is hindered by the strong binding between K+ and ether solvents, leading to [K+-solvent] cointercalation on graphite anodes. Herein, we propose a partially and weakly solvating electrolyte (PWSE) wherein the local solvation environment of the conventional 1,2-dimethoxyethane (DME)-based electrolyte is efficiently reconfigured by a partially and weakly solvating diethoxy methane (DEM) cosolvent. For the PWSE in particular, DEM partially participates in the solvation shell and weakens the chelation between K+ and DME, facilitating desolvation and suppressing cointercalation behavior. Notably, the solvation structure of the DME-based electrolyte is transformed into a more cation-anion-cluster-dominated structure, consequently promoting thin and stable solid-electrolyte interphase (SEI) generation. Benefiting from optimized solvation and SEI generation, the PWSE enables a graphite electrode with reversible K+ (de)intercalation (for over 1000 cycles) and K with reversible plating/stripping (the K||Cu cell with an average Coulombic efficiency of 98.72% over 400 cycles) and dendrite-free properties (the K||K cell operates over 1800 h). We demonstrate that rational PWSE design provides an approach to tailoring electrolytes toward stable PIBs.

Interior-Confined Vacancy in Potassium Manganese Hexacyanoferrate for Ultra-Stable Potassium-Ion Batteries

Metal hexacyanoferrates (HCFs) are viewed as promising cathode materials for potassium-ion batteries (PIBs) because of their high theoretical capacities and redox potentials. However, the development of an HCF cathode with high cycling stability and voltage retention is still impeded by the unavoidable Fe(CN)6 vacancies (VFeCN) and H2O in the materials. Here, a repair method is proposed that significantly reduces the VFeCN content in potassium manganese hexacyanoferrate (KMHCF) enabled by the reducibility of sodium citrate and removal of ligand H2O at high temperature (KMHCF-H). The KMHCF-H obtained at 90 °C contains only 2% VFeCN, and the VFeCN is concentrated in the lattice interior. Such an integrated Fe-CN-Mn surface structure of the KMHCF-H cathode with repaired surface VFeCN allows preferential decomposition of potassium bis(fluorosulfonyl)imide (KFSI) in the electrolyte, which constitutes a dense anion-dominated cathode electrolyte interphase (CEI) , inhibiting effectively Mn dissolution into the electrolyte. Consequently, the KMHCF-H cathode exhibits excellent cycling performance for both half-cell (95.2 % at 0.2 Ag-1 after 2000 cycles) and full-cell (99.4 % at 0.1 Ag-1 after 200 cycles). This thermal repair method enables scalable preparation of KMHCF with a low content of vacancies, holding substantial promise for practical applications of PIBs.

Elastic MXene conductive layers and electrolyte engineering enable robust potassium storage

The precisely engineered structures of materials greatly influence the manifestation of their properties. For example, in the process of alkali metal ion storage, a carefully designed structure capable of accommodating inserted and extracted ions will improve the stability of material cycling. The present study explores the uniform distribution of self-grown carbon nanotubes to provide structural support for the conductive and elastic MXene layers of Ti3C2Tx-Co@NCNTs. Furthermore, a compatible electrolyte system has been optimized by analyzing the solvation structure and carefully regulating the component in the solid electrolyte interphase (SEI) layer. Mechanistic studies demonstrate that the decomposition predominantly controlled by FSI- leads to the formation of a robust inorganic SEI layer enriched with KF, thus effectively inhibiting irreversible side reactions and major structural deterioration. Confirming our expectations, Ti3C2Tx-Co@NCNTs exhibits an impressive reversible capacity of 260 mA h g-1, even after 2000 cycles at 500 mA g-1 in 1 M KFSI (DME), surpassing most MXene-based anodes reported for PIBs. Additionally, density functional theory (DFT) calculations verify the superior electronic conductivity and lower K+ diffusion energy barriers of the novel superstructure of Ti3C2Tx-Co@NCNTs, thereby affirming the improved electrochemical kinetics. This study presents systematic evaluation methodologies for future research on MXene-based anodes in PIBs.

Novel Bismuth Nanoflowers Encapsulated in N-Doped Carbon Frameworks as Superb Composite Anodes for High-Performance Sodium-Ion Batteries

Bismuth (Bi) has attracted attention as a promising anode for sodium-ion batteries (SIBs) owing to its suitable potential and high theoretical capacity. However, the large volumetric changes during cycling leads to severe degradation of electrochemical performance and limits its practical application. Herein, Bi nanoflowers are encapsulated in N-doped carbon frameworks to construct a novel Bi@NC composite via a facile solvothermal method and carbonization strategy. The well-designed composite structure endows the Bi@NC with uniformly dispersed Bi nanoflowers to alleviate the attenuation while the N-doped carbon frameworks improve the conductivity and ion transport of the whole electrode. As for sodium-ion half-cell, the electrode exhibits a high specific capacity (384.8 mAh g-1 at 0.1 A g-1 ) and excellent rate performance (341.5 mAh g-1 at 10 A g-1 ), and the capacity retention rate still remains at 94.9% after 5000 cycles at 10 A g-1 . Furthermore, the assembled full-cell with Na3 V2 (PO4 )3 cathode and Bi@NC anode can deliver a high capacity of 251.5 mAh g-1 at 0.1 A g-1 , and its capacity attenuates only 0.009% in each cycle after 2000 times at 5.0 A g-1 . This work offers a convenient, low-cost, and eco-friendliness approach for high-performance electrodes in the field of sodium ion electrochemical storage technology.

Solvation Structure Modulation of High-Voltage Electrolyte for High-Performance K-Based Dual-Graphite Battery

Due to the advantages of dual-ion batteries (DIBs) and abundant resources, potassium-based dual-carbon batteries (K-DCBs) have wide application prospects. However, conventional carbonate ester-based electrolyte systems have obvious drawbacks such as poor oxidation resistance and difficulty in sustaining the anion intercalation process at high voltages, which seriously affect the capacity and cycle performance of K-DCBs. Therefore, a rational design of more efficient novel electrolyte systems is urgently required to realize high-performance K-DCBs. Herein, a solvation structure modulation strategy for the K-DCB electrolyte systems is reported. Consequently, substantial K⁺ ion storage improvement at the graphite anode and enhanced bis(fluorosulfonyl)imide anion (FSI^- ) intercalation capacity at the graphite cathode are successfully realized simultaneously. As a proof-of-concept, the assembled K-DCB exhibited a discharge capacity of 103.4 mAh g^-1 , and after 400 cycles, ≈90% capacity retention is observed. Moreover, the energy density of the K-DCB full cell reached 157.6 Wh kg^-1 , which is the best performance in reported K-DCBs till date. This study demonstrates the effectiveness of solvation modulation in improving the performance of K-DCBs.

Understanding the Predominant Potassium-Ion Intercalation Mechanism of Single-Phased Bimetal Oxides by in Situ Magnetometry

The electrochemical performance of electrode materials is largely dependent on the structural and chemical evolutions during the charge-discharge processes. Hence, revealing ion storage chemistry could enlighten mechanistic understanding and offer guidance for rational design for energy storage materials. Here, we investigate the mechanisms of potassium (K)-ion storage in the promising bimetal oxide materials by in situ magnetometry. We focus on a single-phased hollow FeTiO₃ (SPH-FTO) hexagonal prism synthesized through a complexing-reagent assisted approach and find that the K-ion storage in this compound occurs predominantly with an intercalation mechanism and fractionally a conversion mechanism. We also demonstrate a K-ion hybrid capacitor assembled with the prepared SPH-FTO hexagonal prism anode and activated carbon cathode, delivering a high energy density and high power density as well as extraordinary cycling stability. This new understanding is used to showcase the inherently high K-ion storage properties from the earth-abundant FeTiO₃.

Recent Advances in Polymers for Potassium Ion Batteries

Potassium-ion batteries (KIBs) are considered to be an effective alternative to lithium-ion batteries (LIBs) due to their abundant resources, low cost, and similar electrochemical properties of K⁺ to Li⁺, and they have a good application prospect in the field of large-scale energy storage batteries. Polymer materials play a very important role in the battery field, such as polymer electrode materials, polymer binders, and polymer electrolytes. Here in this review, we focus on the research progress of polymers in KIBs and systematically summarize the research status and achievements of polymer electrode materials, electrolytes, and binders in potassium ion batteries in recent years. Finally, based on the latest representative research of polymers in KIBs, some suggestions and prospects are put forward, which provide possible directions for future research.

Electrolytes for Multivalent Metal-Ion Batteries: Current Status and Future Prospect

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

Weak Cation-Solvent Interactions in Ether-Based Electrolytes Stabilizing Potassium-ion Batteries

Conventional ether-based electrolytes exhibited a low polarization voltage in potassium-ion batteries, yet suffered from ion-solvent co-intercalation phenomena in a graphite anode, inferior potassium-metal performance, and limited oxidation stability. Here, we reveal that weakening the cation-solvent interactions could suppress the co-intercalation behaviour, enhance the potassium-metal performance, and improve the oxidation stability. Consequently, the graphite anode exhibits K⁺ intercalation behaviour (K||graphite cell operates 200 cycles with 86.6 % capacity retention), the potassium metal shows highly stable plating/stripping (K||Cu cell delivers 550 cycles with average Coulombic efficiency of 98.9 %) and dendrite-free (symmetric K||K cell operates over 1400 hours) properties, and the electrolyte exhibits high oxidation stability up to 4.4 V. The ion-solvent interaction tuning strategy provides a promising method to develop high-performance electrolytes and beyond.

Boosting Interfacial Ion Transfer in Potassium-Ion Batteries via Synergy Between Nanostructured Bi@NC Bulk Anode and Electrolyte

Using high-capacity alloy-type anodes can greatly advance potassium-ion batteries (PIBs). However, the primary limits are unstable solid electrolyte interphase (SEI) and tough interfacial ion transfer associated with large-size K⁺ during electrochemical (de)alloy reactions. Here, we achieve excellent energy storage performance of PIBs via the synergy between a nanostructured Bi@N-doped carbon (Bi@NC) bulk anode and a KPF₆-dimethoxyethane (DME) electrolyte. The Bi@NC material with a high tap density of 3.81 g cm^-3 is prepared by simply pyrolyzing a commercial Bi salt yet affords a favorable nano/microstructure consisting of Bi nanograins confined in 3D ultrathin N-doped carbon shells, facilitating electron/ion transport and structural integrity. Detailed impedance spectroscopy investigation unveils that K⁺ transport through SEI at the Bi@NC anode, rather than the desolvation of K⁺, dominates the interfacial K⁺ transfer. More importantly, spectroscopic and microscopic characterizations provide clear evidence that the interplay between Bi@NC anode and optimized KPF₆-DME electrolyte can produce a unique SEI layer containing Bi³⁺-solvent complex that enables the activation energy of interfacial K⁺ transfer as low as 25.9 kJ mol^-1, thereby ultrafast charge transfer at Bi@NC. Consequently, the Bi@NC anode in half cells achieves exceptional rate capability (206 mAh g^-1 or 784 mAh cm^-3 at 120C) accompanied by high specific capacity (331 mAh g^-1 or 1261 mAh cm^-3) and long cycle life (running 1400 cycles at 15C with a tiny capacity fading rate of 0.013% per cycle). Moreover, the Bi@NC anode and KPF₆-DME electrolyte are also compatible with a potassium Prussian blue cathode and assembled full PIBs achieve stable cyclability (87.3% capacity retention after 100 cycles at 2.5C) and excellent rate performance (65.1% capacity retention upon increasing rates from 1 to 20C).

Utilizing an Oxygen-Rich Interface by Hydroxyapatite to Regulate the Linear Diffusion for the Stable Solid-State Electrolytes

Improving dissociation and diffusion of lithium ions is the key to solving the practical application of polymer-based solid-state electrolytes (SSE). Here, a low-cost three-dimensional hydroxyapatite (HAP) nanowire is used in polyethene oxide to obtain an enhanced lithium-ion electrolyte. The oxygen-rich interface of HAP provides an integrated dissociation-diffusion platform for lithium salts. The TFSI- anions tend to coordinate with calcium ions, which makes it easier for lithium ions to escape and stay in a free state. The lateral nucleus in the HAP polyethene electrolyte regulates the diffusion from spherical diffusion into linear planar diffusion, which is confirmed by chronoamperometry curves and in situ observation. The stability of the electrolyte at high voltages is improved by inhibiting the superoxide radicals of polyethene oxide chains, which is demonstrated by nuclear magnetic resonance and electron paramagnetic resonance spectroscopy methods. The initial specific charge capacity of the Li/SPE/LiFePO4 cell with HAP-modified polyethene oxide at 2 C is 148.8 mA h/g, and its initial Coulombic efficiency is 95.17%. After 100 cycles, the specific discharge capacity is 125.5 mA h/g with 99.91% retention per cycle. This oxygen-rich interface strategy would guide the discovery of novel materials for polymer-based SSE.

The effects of solvents on the physical and electrochemical properties of potassium-ion conducting polymer gel electrolytes

The aim of present work is to investigate the effect of different solvent mixed within poly (vinylidiene fluoride-hexafluoropropylene) (PVDF-HFP) based Potassium ion conducting polymer gel electrolytes. The samples are prepared using solution casting method and the comparative behavior of adding carbonate and glyme in PVDF-HFP/KClO4 matrix is investigated. Subsequently, polymer gel electrolytes are characterized using X-ray diffractometer to analyze the structural features of the electrolyte films. The XRD results reveal that the prepared electrolyte films using both solvents demonstrate semi-crystalline nature. The surface morphology is studied using scanning electron microscopy and significant changes in surface morphology of the polymer gel electrolyte films is observed on introducing carbonate and glyme solvents. Thermal properties and effects of temperature on the prepared electrolytes is examined using differential scanning calorimetry and investigations reveal significant effect of temperature on the heat flow into the polymer gel electrolytes samples. The weight loss of the electrolyte samples with temperature is studied using Thermogravimetric analysis and it is observed that carbonate and glyme based electrolyte offer weight loss of about 7–8 %. The ionic conductivity of 2.53×10−7 Scm−1 and 3.67×10−4 Scm−1 while electrochemical stability window of ∼2.5 V is obtained for both polymer gel electrolytes with carbonate and glyme based solvents. The reversibility of K-ion has been established using cyclic voltammetry measurements.

Sn-, Sb- and Bi-Based Anodes for Potassium Ion Battery

Owing to the abundant resources of potassium resources, potassium ion batteries (PIBs) hold great potential in various energy storage devices. However, the poor lifespan of PIBs anodes limit their merchant applications. The exploitation of anode materials with high performance is one of the critical factors to the development of PIBs. Metallic Sn-, Sb-, and Bi-based materials, show promising future thanks to their high theoretical capacities and safe working voltage. However, the rapid capacity decay caused by the large K⁺ is still a pivotal challenge. In this review, recent progresses on alloying anodes were summarized. Schemes, such as ultra-small nanoparticles, hetero-element doping, and electrolyte optimization are effective strategies to improve their electrochemical properties. This review provides an outlook on the nanostructures and their synthesis methods for the alloying-type materials, and will stimulate their intensive study for practical application in the near future.

Recent Advances in Layered Metal-Oxide Cathodes for Application in Potassium-Ion Batteries

To meet future energy demands, currently, dominant lithium-ion batteries (LIBs) must be supported by abundant and cost-effective alternative battery materials. Potassium-ion batteries (KIBs) are promising alternatives to LIBs because KIB materials are abundant and because KIBs exhibit intercalation chemistry like LIBs and comparable energy densities. In pursuit of superior batteries, designing and developing highly efficient electrode materials are indispensable for meeting the requirements of large-scale energy storage applications. Despite using graphite anodes in KIBs instead of in sodium-ion batteries (NIBs), developing suitable KIB cathodes is extremely challenging and has attracted considerable research attention. Among the various cathode materials, layered metal oxides have attracted considerable interest owing to their tunable stoichiometry, high specific capacity, and structural stability. Therefore, the recent progress in layered metal-oxide cathodes is comprehensively reviewed for application to KIBs and the fundamental material design, classification, phase transitions, preparation techniques, and corresponding electrochemical performance of KIBs are presented. Furthermore, the challenges and opportunities associated with developing layered oxide cathode materials are presented for practical application to KIBs.

Cardanol-Derived Epoxy Resins as Biobased Gel Polymer Electrolytes for Potassium-Ion Conduction

In this study, biobased gel polymer electrolyte (GPE) membranes were developed via the esterification reaction of a cardanol-based epoxy resin with glutaric anhydride, succinic anhydride, and hexahydro-4-methylphthalic anhydride. Nonisothermal differential scanning calorimetry was used to assess the optimal curing time and temperature of the formulations, evidencing a process activation energy of ∼65-70 kJ mol-1. A rubbery plateau modulus of 0.65-0.78 MPa and a crosslinking density of 2 × 10-4 mol cm-3 were found through dynamic mechanical analysis. Based on these characteristics, such biobased membranes were tested for applicability as GPEs for potassium-ion batteries (KIBs), showing an excellent electrochemical stability toward potassium metal in the -0.2-5 V voltage range and suitable ionic conductivity (10-3 S cm-1) at room temperature. This study demonstrates the practical viability of these biobased materials as efficient GPEs for the fabrication of KIBs, paving the path to increased sustainability in the field of next-generation battery technologies.

Prussian Blue Analogues for Sodium-Ion Batteries: Past, Present, and Future

Prussian blue analogues (PBAs) have attracted wide attention for their application in the energy storage and conversion field due to their low cost, facile synthesis, and appreciable electrochemical performance. At the present stage, most research on PBAs is focused on their material-level optimization, whereas their properties in practical battery systems are seldom considered. This review aims to first provide an overview of the history and parameters of PBA materials and analyze the fundamental principles toward rational design of PBAs, and then evaluate the prospects and challenges for PBAs for practical sodium-ion batteries, hoping to bridge the gap between laboratory research and commercial reality.

Moderate Specific Surface Areas Help Three-Dimensional Frameworks Achieve Dendrite-Free Potassium-Metal Anodes

The inevitable problem of dendrites growth has hampered the further development of K metal anodes. Constructing a three-dimensional anode framework and potassiophilic nanocoating is an effective way to enlarge the specific surface area, reduce the local current density, and inhibit the formation of K dendrites. However, the effects of the electrochemically active surface area (ECSA) of the framework on deposition behavior have not been clarified. Hence, SnS₂ nanosheets with different sizes are loaded on the surface of carbon paper (SnS₂@CP) to improve the potassiophilicity and realize dendrite-free K-metal anodes. Experiments reveal that the size of SnS₂ nanosheets would determine the ECSA of the framework, while the ECSA reveals the relative sizes of specific surface areas of frameworks. Excessive or limited specific surface areas will cause morphological collapse or weak potassiophilicity during potassiation, respectively, thus leading to high nucleation overpotential. The moderate specific surface area and abundant and stable potassiophilic sites prompt the SnS₂@CP framework to achieve uniform electrodeposition of K. A low nucleation overpotential of 11.2 mV and a cycle life of more than 800 h are exhibited at a current density of 0.25 mA cm^-2, indicating the directional strategy for stable and safe K metal anodes.

Bismuth Nanoparticle Embedded in Carbon Skeleton as Anode for High Power Density Potassium-Ion Batteries

Bismuth is a promising anode for potassium-ion batteries (PIBs) due to its suitable redox potential, large theoretical capacity, and superior electronic conductivity. Herein, we report a Bi@C (Bi nanoparticles uniformly embedded in a carbon skeleton) composite anode which delivers a superior rate performance of 244.3 mA h g⁻¹ at 10.0 A g⁻¹ and a reversible capacity of 255.6 mA h g⁻¹ after 200 cycles in an optimized ether-based electrolyte. The outstanding electrochemical performance results from its robust structural design with fast reaction kinetics, which are confirmed by both experimental characterization studies and first-principles calculations. The reversible potassium storage mechanism of the Bi@C composite was also investigated by in situ X-ray diffraction. In addition, the full PIB cell assembled with a Bi@C composite anode and nickel-based Prussian blue analogue cathode exhibits high discharge voltage (3.18 V), remarkable power density (>10 kW kg⁻¹), and an excellent capacity retention of 87.8% after 100 cycles. The results demonstrate that the PIBs with Bi anodes are promising candidates for power-type energy storage devices.

An ultrahigh power density (>10 kW kg⁻¹) potassium-ion full cell was fabricated by using a designed Bi@C composite as the anode. This workproves that potassium-ion batteries are promising candidates for power-type large-scale energy storage devices.

Prospects of Electrode Materials and Electrolytes for Practical Potassium-Based Batteries

Potassium-ion batteries (PIBs) have attracted tremendous attention because of their high energy density and low-cost. As such, much effort has focused on developing electrode materials and electrolytes for PIBs at the material levels. This review begins with an overview of the high-performance electrode materials and electrolytes, and then evaluates their prospects and challenges for practical PIBs to penetrate the market. The current status of PIBs for safe operation, energy density, power density, cyclability, and sustainability is discussed and future studies for electrode materials, electrolytes, and electrode-electrolyte interfaces are identified. It is anticipated that this review will motivate research and development to fill existing gaps for practical potassium-based full batteries so that they may be commercialized in the near future.

Carbon Hollow Tube-Confined Sb/Sb2S3 Nanorod Fragments as Highly Stable Anodes for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) have attracted widespread attention in recent years due to their potential advantages such as low cost and high energy density. However, the large radius of K⁺ and the low potassium storage capacity of some electrode materials limit their development. Antimony (Sb)-based materials are considered to be promising anode materials for PIBs in view of their high K storage capacity and low potassiation potential. Nonetheless, the huge volume variation caused by potassiation/depotassiation often leads to their failure. Previous works have proved that carbon coating and nanostructure design are important means to alleviate the volume effect. Herein, the carbon-coating technology and nanostructure design were combined to prepare a Sb-based nanomaterial with Sb/Sb₂S₃ hybrid nanorod fragments confined in a carbon hollow tube (Sb/Sb₂S₃@CHT). Such a nanostructure is beneficial to alleviate the volume change of the Sb/Sb₂S₃ hybrids while facilitating the kinetics of the electrochemical reaction. As a consequence, the Sb/Sb₂S₃@CHT anode electrode exhibits high rate performance and outstanding cycle stability characterized by retaining a high specific capacity of 400.9 mA h g^-1 after cycling for 200 cycles at 200 mA g^-1.

Heterostructured CoS2/CuCo2S4@N-doped carbon hollow sphere for potassium-ion batteries

Potassium ions batteries (PIBs) have been regarded as a promising choice for electrical energy storage technology due to the wide distribution of potassium resources. However, developing low-cost and robust earth-rich anode materials is still a major challenge for the practical and scalable usage of PIBs. Herein, for the first time, we developed nitrogen doped carbon coating CoS₂/CuCo₂S₄ heterostructure (CoS₂/CuCo₂S₄@NCs) hollow spheres and evaluated as anode for PIBs. The CoS₂ and CuCo₂S₄ heterostructure interface could generate a built-in electric field, which can fasten electrons transportation. The nanostructures could shorten the diffusion length of K⁺ and provide large surface area to contact with electrolytes. Furthermore, the inner hollow sphere morphology along with the carbon layer could accommodate the volume expansion during cycling. What's more, the N-doped carbon could increase the conductivity of the anodes. Benefitting from the above features, the CoS₂/CuCo₂S₄@NCs displays an outstanding rate capability (309 mAh g^-1 at 500 mA g^-1 after 250 cycles) and a long-term cycling life (112 mAh g^-1 at 1000 mA g^-1 after 1000 cycles) in ether-based electrolyte. Conversion reaction mechanism in CoS₂/CuCo₂S₄@NCs anode is also revealed through ex situ XRD characterizations. This work provides a practical direction for investigating metal sulfides as anode for PIBs.

11,11,12,12-tetracyano-9,10-anthraquinonedimethane as a high potential and sustainable cathode for organic potassium-ion batteries

We fabricated a potassium-ion battery by using 11,11,12,12-tetracyano-9,10-anthraquinonedimethane (TCAQ) as the cathode for the first time. Owing to the unique molecular structure and configuration of ionic liquid electrolytes, TCAQ shows a high redox potential of 2.6 V vs. K⁺/K while delivering a capacity of 88 mAh g^-1 at a current density of 17 mA g^-1 and a capacity retention of 61% after 50 cycles. The mechanism of the reaction of TCAQ with K was investigated. The results prove that TCAQ holds great promise for broad applications in potassium-ion batteries while revealing new scientific insights into K⁺-organic cathode batteries.

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

Metal-ion batteries are capable of delivering high energy density with a longer lifespan. However, they are subject to several issues limiting their utilization. One critical impediment is the budding and extension of solid protuberances on the anodic surface, which hinders the cell functionalities. These protuberances expand continuously during the cyclic processes, extending through the separator sheath and leading to electrical shorting. The progression of a protrusion relies on a number of in situ and ex situ factors that can be evaluated theoretically through modeling or via laboratory experimentation. However, it is essential to identify the dynamics and mechanism of protrusion outgrowth. This review article explores recent advances in alleviating metal dendrites in battery systems, specifically alkali metals. In detail, we address the challenges associated with battery breakdown, including the underlying mechanism of dendrite generation and swelling. We discuss the feasible solutions to mitigate the dendrites, as well as their pros and cons, highlighting future research directions. It is of great importance to analyze dendrite suppression within a pragmatic framework with synergy in order to discover a unique solution to ensure the viability of present (Li) and future-generation batteries (Na and K) for commercial use.

Recent Advances and Perspectives on the Polymer Electrolytes for Sodium/Potassium-Ion Batteries

Owing to the low cost of sodium/potassium resources and similar electrochemical properties of Na⁺ /K⁺ to Li⁺ , sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) are regarded as promising alternatives to lithium-ion batteries (LIBs) in large-scale energy storage field. However, traditional organic liquid electrolytes bestow SIBs/KIBs with serious safety concerns. In contrast, quasi-/solid-phase electrolytes including polymer electrolytes (PEs) and inorganic solid electrolytes (ISEs) show great superiority of high safety. However, the poor processibility and relatively low ionic conductivity of Na⁺ and K⁺ ions limit the further practical applications of ISEs. PEs combine some merits of both liquid-phase electrolytes and ISEs, and present great potentials in next-generation energy storage systems. Considerable efforts have been devoted to improving their overall properties. Nevertheless, there is still a lack of an in-depth and comprehensive review to get insights into mechanisms and corresponding design strategies of PEs. Herein, the advantages of different electrolytes, particularly PEs are first minutely reviewed, and the mechanism of PEs for Na⁺ /K⁺ ion transfer is summarized. Then, representative researches and recent progresses of SIBs/KIBs based on PEs are presented. Finally, some suggestions and perspectives are put forward to provide some possible directions for the follow-up researches.

Bismuth Nanoparticles Confined in Carbonaceous Nanospheres as Anodes for High-Performance Potassium-Ion Batteries

Bismuth (Bi) has been considered as a promising alloying-type anode for potassium-ion batteries (PIBs), owing to its high theoretical capacity and suitable working voltage plateaus. However, Bi suffers from dramatic volume fluctuation and significant pulverization during the discharge/charge processes, resulting in fast capacity decay. Herein, we synthesize Bi nanoparticles confined in carbonaceous nanospheres (denoted as Bi@C) for PIBs by first utilizing BiOCl nanoflakes as a hard template and a Bi precursor. The construction of the loose structure buffers the mechanical stresses resulting from the volume expansion of Bi during the alloying reaction and avoids the fracture of the electrode structure, thus improving the cycling performance. Moreover, the carbonaceous layers increase the electronic conductivity and disperse the Bi nanoparticles, enhancing the charge transportation and ionic diffusion, which further promotes the rate capability of Bi@C. It exhibits a superior capacity (389 mAh g^-1 at 100 mA g^-1 after 100 cycles), excellent cycling stability (206 mAh g^-1 at 500 mA g^-1 over 1000 cycles), and an improved rate capability (182 mAh g^-1 at 2.0 A g^-1). This work provides a new structuring strategy in alloying materials for boosting reversible and stable potassium-ion storage.