Bi-Sb Nanocrystals Embedded in Phosphorus as High-Performance Potassium Ion Battery Electrodes

The Enormous Potential of Sodium/Potassium-Ion Batteries as the Mainstream Energy Storage Technology for Large-Scale Commercial Applications

Cost-effectiveness plays a decisive role in sustainable operating of rechargeable batteries. As such, the low cost-consumption of sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) provides a promising direction for "how do SIBs/PIBs replace Li-ion batteries (LIBs) counterparts" based on their resource abundance and advanced electrochemical performance. To rationalize the SIBs/PIBs technologies as alternatives to LIBs from the unit energy cost perspective, this review gives the specific criteria for their energy density at possible electrode-price grades and various battery-longevity levels. The cost ($ kWh-1 cycle-1) advantage of SIBs/PIBs is ascertained by the cheap raw-material compensation for the cycle performance deficiency and the energy density gap with LIBs. Furthermore, the cost comparison between SIBs and PIBs, especially on cost per kWh and per cycle, is also involved. This review explicitly manifests the practicability and cost-effectiveness toward SIBs are superior to PIBs whose commercialization has so far been hindered by low energy density. Even so, the huge potential on sustainability of PIBs, to outperform SIBs, as the mainstream energy storage technology is revealed as long as PIBs achieve long cycle life or enhanced energy density, the related outlook of which is proceeded as the next development directions for commercial applications.

Homogeneous Adsorption of Multiple Potassiation Products of Red Phosphorus Anode toward Stable Potassium Storage

Potassium ion batteries (PIBs) are a viable alternative to lithium-ion batteries for energy storage. Red phosphorus (RP) has attracted a great deal of interest as an anode for PIBs owing to its cheapness, ideal electrode potential, and high theoretical specific capacity. However, the direct preparation of phosphorus-carbon composites usually results in exposure of the RP to the exterior of the carbon layer, which can lead to the deactivation of the active material and the production of "dead phosphorus". Here, the advantage of the π-π bond conjugated structure and high catalytic activity of metal phthalocyanine (MPc) is used to prepare MPc@RP/C composites as a highly stable anode for PIBs. It is shown that the introduction of MPc greatly improves the uneven distribution of the carbon layer on RP, and thus improves the initial Coulombic efficiency (ICE) of PIBs (the ICE of FePc@RP/C is 75.5% relative to 62.9% of RP/C). The addition of MPc promotes the growth of solid electrolyte interphase with high mechanical strength, improving the cycle stability of PIBs (the discharge-specific capacity of FePc@RP/C is 411.9 mAh g-1 after 100 cycles at 0.05 A g-1). Besides, density functional theory theoretical calculations show that MPc exhibits homogeneous adsorption energies for multiple potassiation products, thereby improving the electrochemical reactivity of RP. The use of organic molecules with high electrocatalytic activity provides a universal approach for designing superior high-capacity, large-volume expansion anodes for PIBs.

3D Dense Encapsulated Architecture of 2D Bi Nanosheets Enabling Potassium-Ion Storage with Superior Volumetric and Areal Capacities

2D alloy-based anodes show promise in potassium-ion batteries (PIBs). Nevertheless, their low tap density and huge volume expansion cause insufficient volumetric capacity and cycling stability. Herein, a 3D highly dense encapsulated architecture of 2D-Bi nanosheets (HD-Bi@G) with conducive elastic networks and 3D compact encapsulation structure of 2D nano-sheets are developed. As expected, HD-Bi@G anode exhibits a considerable volumetric capacity of 1032.2 mAh cm-3, stable long-life span with 75% retention after 2000 cycles, superior rate capability of 271.0 mAh g-1 at 104 C, and high areal capacity of 7.94 mAh cm-2 (loading: 24.2 mg cm-2) in PIBs. The superior volumetric and areal performance mechanisms are revealed through systematic kinetic investigations, ex situ characterization techniques, and theorical calculation. The 3D high-conductivity elastic network with dense encapsulated 2D-Bi architecture effectively relieves the volume expansion and pulverization of Bi nanosheets, maintains internal 2D structure with fast kinetics, and overcome sluggish ionic/electronic diffusion obstacle of ultra-thick, dense electrodes. The uniquely encapsulated 2D-nanosheet structure greatly reduces K+ diffusion energy barrier and accelerates K+ diffusion kinetics. These findings validate a feasible approach to fabricate 3D dense encapsulated architectures of 2D-alloy nanosheets with conductive elastic networks, enabling the design of ultra-thick, dense electrodes for high-volumetric-energy-density energy storage.

Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

Rational Design of Multinary Metal Chalcogenide Bi0.4 Sb1.6 Te3 Nanocrystals for Efficient Potassium Storage

Multinary metal chalcogenides hold considerable promise for high-energy potassium storage due to their numerous redox reactions. However, challenges arise from issues such as volume expansion and sluggish kinetics. Here, a design featuring a layered ternary Bi0.4 Sb1.6 Te3 anchored on graphene layers as a composite anode, where Bi atoms act as a lattice softening agent on Sb, is presented. Benefiting from the lattice arrangement in Bi0.4 Sb1.6 Te3 and structure, Bi0.4 Sb1.6 Te3 /graphene exhibits a mitigated expansion of 28% during the potassiation/depotassiation process and demonstrates facile K+ ion transfer kinetics, enabling long-term durability of 500 cycles at various high rates. Operando synchrotron diffraction patterns and spectroscopies including in situ Raman, ex situ adsorption, and X-ray photoelectron reveal multiple conversion and alloying/dealloying reactions for potassium storage at the atomic level. In addition, both theoretical calculations and electrochemical examinations elucidate the K+ migration pathways and indicate a reduction in energy barriers within Bi0.4 Sb1.6 Te3 /graphene, thereby suggesting enhanced diffusion kinetics for K+ . These findings provide insight in the design of durable high-energy multinary tellurides for potassium storage.

Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → β Phase Transition

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, α-MnSe nanorods derived from δ-MnO2 (δ-α-MnSe) are constructed as anodes for SIBs. It is verified that α-MnSe will be transferred into β-MnSe after the initial Na-ion insertion/extraction, and δ-α-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free α-MnSe can drive the lattice distortion to phase transition (alpha → beta) in thermodynamics and dynamics. The formed β-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the δ-α-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh·kg-1 and outstanding cyclability demonstrate the applicability of δ-α-MnSe anode.

Novel Ultra-Stable 2D SbBi Alloy Structure with Precise Regulation Ratio Enables Long-Stable Potassium/Lithium-Ion Storage

The inferior cycling stabilities or low capacities of 2D Sb or Bi limit their applications in high-capacity and long-stability potassium/lithium-ion batteries (PIBs/LIBs). Therefore, integrating the synergy of high-capacity Sb and high-stability Bi to fabricate 2D binary alloys is an intriguing and challenging endeavor. Herein, a series of novel 2D binary SbBi alloys with different atomic ratios are fabricated using a simple one-step co-replacement method. Among these fabricated alloys, the 2D-Sb0.6 Bi0.4 anode exhibits high-capacity and ultra-stable potassium and lithium storage performance. Particularly, the 2D-Sb0.6 Bi0.4 anode has a high-stability capacity of 381.1 mAh g-1 after 500 cycles at 0.2 A g-1 (≈87.8% retention) and an ultra-long-cycling stability of 1000 cycles (0.037% decay per cycle) at 1.0 A g-1 in PIBs. Besides, the superior lithium and potassium storage mechanism is revealed by kinetic analysis, in-situ/ex-situ characterization techniques, and theoretical calculations. This mainly originates from the ultra-stable structure and synergistic interaction within the 2D-binary alloy, which significantly alleviates the volume expansion, enhances K+ adsorption energy, and decreases the K+ diffusion energy barrier compared to individual 2D-Bi or 2D-Sb. This study verifies a new scalable design strategy for creating 2D binary (even ternary) alloys, offering valuable insights into their fundamental mechanisms in rechargeable batteries.

Oxygen Vacancy-Tailored Schottky Heterojunction Activates Interface Dipole Amplification and Carrier Inversion for High-Performance Potassium-Ion Batteries

An oxygen vacancy-tailored Schottky heterostructure composed of polyvinylpyrrolidone-assisted Bi2 Sn2 O7 (PVPBSO) nanocrystals and moderate work function graphene (mWFG, WF = 4.36 eV) is designed, which in turn intensifies the built-in voltage and interface dipole across the space charge region (SCR), leading to the inversion of majority carriers for facilitating K+ transport/diffusion behaviors. Thorough band-alignment experiments and interface simulations reveal the dynamics between deficient BSO and mWFG, and how charge redistribution within the SCR leads to carrier inversion, demonstrating the impact of different defect engineering degrees on the amplification of Schottky junctions. The ordered transport of bipolar carriers can boost electrons and K ions easily passing through the inner and outer surfaces of the heterostructure. With high activity and low resistance in electrochemical reactions, the PVPBSO/mWFG exhibits an attractive capacity of 430 mA h g-1 and a rate capability exceeding 2000 mA g-1 , accompanied by minimal polarization and efficient utilization of conversion-alloying reactions. The substantial cell capacity and high-redox plateau of PVPBSO/mWFG//PB contribute to the practical feasibility of high-energy full batteries, offering long-cycle retention and high-voltage output. This study emphasizes the direct importance of interface and junction engineering in improving the efficiency of diverse electrochemical kinetic and diffusion processes for potassium-ion batteries.

Bismuth Telluride Nanoplates Hierarchically Confined by Graphene and N-Doped C as Conversion-Alloying Anode Materials for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) have broad application prospects in the field of electric energy storage systems because of its abundant K reserves, and similar "rocking chair" operating principle as lithium-ion batteries (LIBs). Aiming to the large volume expansion and sluggish dynamic behavior of anode materials for storing large sized K-ion, bismuth telluride (Bi2 Te3 ) nanoplates hierarchically encapsulated by reduced graphene oxide (rGO), and nitrogen-doped carbon (NC) are constructed as anodes for PIBs. The resultant Bi2 Te3 @rGO@NC architecture features robust chemical bond of Bi─O─C, tightly physicochemical confinement effect, typical conductor property, and enhanced K-ion adsorption ability, thereby producing superior electrochemical kinetics and outstanding morphological and structural stability. It is visually elucidated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that conversion-alloying dual-mechanism plays a significant role in K-ion storage, allowing 12 K-ion transport per formular unit employing Bi as redox site. Thus, the high first reversible specific capacity of 322.70 mAh g-1 at 50 mA g-1 , great rate capability and cyclic stability can be achieved for Bi2 Te3 @rGO@NC. This work lays the foundation for an in-depth understanding of conversion-alloying mechanism in potassium-ion storage.

Co-activation for enhanced K-ion storage in battery anodes

The relative natural abundance of potassium and potentially high energy density has established potassium-ion batteries as a promising technology for future large-scale global energy storage. However, the anodes' low capacity and high discharge platform lead to low energy density, which impedes their rapid development. Herein, we present a possible co-activation mechanism between bismuth (Bi) and tin (Sn) that enhances K-ion storage in battery anodes. The co-activated Bi-Sn anode delivered a high capacity of 634 mAh g-1, with a discharge plateau as low as 0.35 V, and operated continuously for 500 cycles at a current density of 50 mA g-1, with a high Coulombic efficiency of 99.2%. This possible co-activation strategy for high potassium storage may be extended to other Na/Zn/Ca/Mg/Al ion battery technologies, thus providing insights into how to improve their energy storage ability.

Firmly interlocked Janus-type metallic Ni3Sn2S2-carbon nanotube heterostructure suppresses polysulfide dissolution and Sn aggregation

Ternary transition-metal tin chalcogenides, with their diverse compositions, abundant constituents, high theoretical capacities, acceptable working potentials, excellent conductivities, and synergistic active/inactive multi-components, hold promise as anode materials for metal-ion batteries. However, abnormal aggregation of Sn nanocrystals and the shuttling of intermediate polysulfides during electrochemical tests detrimentally affect the reversibility of redox reactions and lead to rapid capacity fading within a limited number of cycles. In this study, we present the development of a robust Janus-type metallic Ni₃Sn₂S₂-carbon nanotube (NSSC) heterostructured anode for Li-ion batteries (LIBs). The synergistic effects of Ni₃Sn₂S₂ nanoparticles and a carbon network successfully generate abundant heterointerfaces with steady chemical bridges, thereby enhancing ion and electron transport, preventing the aggregation of Ni and Sn nanoparticles, mitigating the oxidation and shuttling of polysulfides, facilitating the reforming of Ni₃Sn₂S₂ nanocrystals during delithiation, creating a uniform solid-electrolyte interphase (SEI) layer, protecting the mechanical integrity of electrode materials, and ultimately enabling highly reversible lithium storage. Consequently, the NSSC hybrid exhibits an excellent initial Coulombic efficiency (ICE > 83 %) and superb cyclic performance (1218 mAh/g after 500 cycles at 0.2 A/g and 752 mAh/g after 1050 cycles at 1 A/g). This research provides practical solutions for the intrinsic challenges associated with multi-component alloying and conversion-type electrode materials in next-generation metal-ion batteries.

SnCo Nanoparticles Loaded in Hollow Carbon Spheres Interlinked by N-Doped Carbon Fibers for High-Performance Sodium-Ion Batteries

The development of Sn-based materials with electrochemically inactive matrices is a novel strategy to alleviate the volume expansion and giant structure strain/stress during the sodiation/desodiation process. In this work, a freestanding membrane based on the unique bean pod-like host composed by nitrogen-doped carbon fibers and hollow carbon spheres (HCSs) encapsulated with SnCo nanoparticles is synthesized by electrospinning (B-SnCo/NCFs). In this unique bean pod-like structure, Sn acts as a host for Na⁺ storage, while the Co plays the important role of an electrochemically inactive matrix that can not only buffer the volume variations but also inhibit aggregation and particle growth of the Sn phase during the electrochemical Na-Sn alloying process. Meanwhile, the introduction of hollow carbon spheres can not only provide enough sufficient void space to withstand the volume expansion during the (de)sodiation processes but also improve the conductivity of the anode along the carbon fibers. Furthermore, the B-SnCo/NCF freestanding membrane can increase the contact area between the active material and the electrolyte, which can provide more active sites during the cycling process. When used as an anode material for Na-ion batteries, the freestanding B-SnCo/NCF anode exhibits an outstanding rate capacity of 243.5 mA h g^-1 at 1.6 A g^-1and an excellent specific capacity of 351 mA h g^-1 at 0.1 A g^-1 for 300 cycles.

Understanding the Highly Reversible Potassium Storage of Hollow Ternary (Bi-Sb)2S3@N-C Nanocube

Metal sulfide anodes have aroused much attention in potassium ion batteries (PIBs) owing to their high theoretical capacities, but the sluggish kinetics and inferior cycling performance caused by severe volumetric change and particle pulverization greatly hinder their further development. Herein, robust hollow structure design together with phase structure engineering endow (Bi-Sb)₂S₃@N-C anode with superior (de)potassiation kinetics and excellent electrochemical performances in PIBs. Specifically, in situ X-ray diffraction combined with density functional theory calculations and ex situ X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy (TEM) analyses indicated a fresh reaction mechanism of (Bi-Sb)₂S₃ anode with a distinctive multistep (de)potassiation route along (003) plane of (Bi,Sb) alloy thanks to the Bi-Sb phase regulation in (Bi-Sb)₂S₃ anode, ensuring it with superior reaction kinetics. Moreover, in situ TEM characterization revealed the advantages of the hollow nanostructure with carbon shell, facilitating fast ion transport kinetics and high tolerance of volume change as well as enabling the structural integrity of electrode material during (de)potassiation. As a result, the (Bi-Sb)₂S₃ hollow nanocube with N-doped carbon shell ((Bi-Sb)₂S₃@N-C) delivers a high initial Coulombic efficiency of 66.3%, a great rate performance of 289 mAh g^-1 at 2.0 A g^-1, and an ultralong cycling life (89% retention after 220 cycles at 0.1 A g^-1 and 85% retention after 1600 cycles at 2.0 A g^-1) in PIBs. Furthermore, the full cell of (Bi-Sb)₂S₃@N-C//PTCDA affords a high reversible capacity of 281 mA h g^-1 at 1.0 A g^-1 after 300 cycles. This work combines structural design and in situ techniques, proving a successful nanostructure engineering strategy to rationalize alloy-type electrode materials for PIBs.

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).

In Situ Atomic-Scale Observation of Electrochemical (De)potassiation in Te Nanowires

Potassium-ion batteries (PIBs) have great potential in energy storage due to their high abundance and low cost of potassium resources. Tellurium (Te) is a promising PIB cathode due to its high volumetric capacity and good electronic conductivity. However, the electrochemical (de)potassiation mechanism of Te remains elusive due to the lack of an effective method of directly observing the dynamic reaction at atomic resolution. Here, the phase transformations of single crystal Te on (de)potassiation are clearly revealed by in situ high-resolution transmission electron microscopy and electron diffraction. Te undergoes a consecutive phase transformation during potassiation: from Te to K₂ Te₃ in the initial potassiation, and then part of the K₂ Te₃ to K₅ Te₃ on further potassiation. The reaction has extremely high reversibility in the following depotassiation. By atomic-scale observation, an anisotropic reaction mechanism where K⁺ intercalates into Te crystalline lattice preferentially through the (001) plane (having a large d-spacing) is established during potassiation. While in the depotassiation process, K ions extract from the polycrystalline K_x Te along the same diffusion path to form single crystal Te, indicating the potassium storage is highly reversible. The strong orientation-dependent (de)potassiation mechanism revealed by this work provides implications for the future design of nanostructured cathodes for high-performance PIBs.

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 progress on Sb- and Bi-based chalcogenide anodes for potassium ion batteries

Potassium ion batteries (PIBs) are potential alternative energy storage systems to lithium ion batteries (LIBs), due to elemental abundance of potassium, low cost and similar working principle to LIBs. Recently, metal chalcogenides (MCs) have gained enormous interests, especially antimony (Sb)-, bismuth (Bi) -based chalcogenides because they were able to undergo alloying/conversion dual mechanism, which can provide higher specific capacity and energy density (K 3 Sb~660 mA h g -1 , K 3 Bi~385 mA h g -1 ). However, several challenges hinder the development of Sb-, Bi-based chalcogenide anode materials for PIBs , such as huge volume expansion during potassiation, unstable solid-electrolyte interface (SEI), slow reaction kinetics, and polychalcogenide-induced shuttle effect . In this review, the current state-of-the-art Sb-, Bi-based chalcogenides are comprehensively summarized, including the reaction mechanism, electrochemical performance, ingenious nanostructures, electrolyte systems, and prospects for future development. This review contributes to understanding the K + storage mechanism and the interaction between active materials and electrolytes, providing guidance and foundation for the design of next-generation high-performance PIBs.

Structure Engineering of BiSbSx Nanocrystals Embedded within Sulfurized Polyacrylonitrile Fibers for High Performance of Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are regarded as promising candidates in next-generation energy storage technology; however, the electrode materials in PIBs are usually restricted by the shortcomings of large volume expansion and poor cycling stability stemming from a high resistance towards diffusion and insertion of large-sized K ions. In this study, BiSbS_x nanocrystals are rationally integrated with sulfurized polyacrylonitrile (SPAN) fibres through electrospinning technology with an annealing process. Such a unique structure, in which BiSbS_x nanocrystals are embedded inside the SPAN fibre, affords multiple binding sites and a short diffusion length for K⁺ to realize fast kinetics. In addition, the molecular structure of SPAN features robust chemical interactions for stationary diffluent discharge products. Thus, the electrode demonstrates a superior potassium storage performance with an excellent reversible capacity of 790 mAh g^-1 (at 0.1 A g^-1 after 50 cycles) and 472 mAh g^-1 (at 1 A g^-1 after 2000 cycles). It's one of the best performances for metal dichalcogenides anodes for PIBs to date. The unusual performance of the BiSbS_x @SPAN composite is attributed to the synergistic effects of the judicious nanostructure engineering of BiSbS_x nanocrystals as well as the chemical interaction and confinement of SPAN fibers.

Crystal Facet and Architecture Engineering of Metal Oxide Nanonetwork Anodes for High-Performance Potassium Ion Batteries and Hybrid Capacitors

Metal oxides are considered as prospective dual-functional anode candidates for potassium ion batteries (PIBs) and hybrid capacitors (PIHCs) because of their abundance and high theoretic gravimetric capacity; however, due to the inherent insulating property of wide band gaps and deficient ion-transport kinetics, metal oxide anodes exhibit poor K⁺ electrochemical performance. In this work, we report crystal facet and architecture engineering of metal oxides to achieve significantly enhanced K⁺ storage performance. A bismuth antimonate (BiSbO₄) nanonetwork with an architecture of perpendicularly crossed single crystal nanorods of majorly exposed (001) planes are synthesized via CTAB-mediated growth. (001) is found to be the preferential surface diffusion path for superior adsorption and K⁺ transport, and in addition, the interconnected nanorods gives rise to a robust matrix to enhance electrical conductivity and ion transport, as well as buffering dramatic volume change during insertion/extraction of K⁺. Thanks to the synergistic effect of facet and structural engineering of BiSbO₄ electrodes, a stable dual conversion-alloying mechanism based on reversible six-electron transfer per formula unit of ternary metal oxides is realized, proceeding by reversible coexistence of potassium peroxide conversion reactions (KO₂↔K₂O) and Bi_xSb_y alloying reactions (BiSb ↔ KBiSb ↔ K₃BiSb). As a result, BiSbO₄ nanonetwork anodes show outstanding potassium ion storage in terms of capacity, cycling life, and rate capability. Finally, the implementation of a BiSbO₄ nanonetwork anode in the state-of-the-art full cell configuration of both PIBs and PIHCs shows satisfactory performance in a Ragone plot that sheds light on their practical applications for a wide range of K⁺-based energy storage devices. We believe this study will propose a promising avenue to design advanced hierarchical nanostructures of ternary or binary conversion-type materials for PIBs, PIHCs, or even for extensive energy storage.

Bi@C Nanospheres with the Unique Petaloid Core-Shell Structure Anchored on Porous Graphene Nanosheets as an Anode for Stable Sodium- and Potassium-Ion Batteries

Bismuth (Bi) has emerged as a prospective candidate as Na-ion and potassium-ion battery anodes because of its unique advantages of low cost, high theoretical gravimetric capacity (386 mAh g^-1), and superior volumetric capacity (3800 mAh cm^-3). However, the low electronic conductivity and the huge volume expansion of Bi during the alloying/dealloying reactions are extremely detrimental to cycling stability, which seriously hinder its practical application. To overcome these issues, we propose a rational design: Bi@C nanospheres with the unique petaloid core-shell structure are synthesized in one step for the first time and then combined with different contents of graphene (GR) nanosheets to form the composites Bi@C@GR. The Bi@C nanospheres with a core-shell structure are beneficial to shortening the transmission path of electrons/ions and reducing the risk from structural rupture of the particles during cycling. In addition, the combination of Bi@C nanospheres and porous GR could greatly improve the conductivity and prevent the aggregation of particles, which is conducive to better cycling stability and rate performance. Consequently, Bi@C@GR-2 presents a superior reversible capacity for sodium storage (300 mAh g^-1 over 80 cycles) and potassium storage (200 mAh g^-1 over 70 cycles) at 0.1 A g^-1. Furthermore, in situ electrochemical impedance spectroscopy and ex situ transmission electron microscopy are carried out to analyze and reflect the kinetic reaction mechanism and the phase change of the Bi@C@GR-2 electrode during the charge/discharge processes.

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.

Achieving High-Performance 3D K+ -Pre-intercalated Ti3 C2 Tx MXene for Potassium-Ion Hybrid Capacitors via Regulating Electrolyte Solvation Structure

The development of high-performance anode materials for potassium-based energy storage devices with long-term cyclability requires combined innovations from rational material design to electrolyte optimization. A three-dimensional K⁺ -pre-intercalated Ti₃ C₂ T_x MXene with enlarged interlayer distance was constructed for efficient electrochemical potassium-ion storage. We found that the optimized solvation structure of the concentrated ether-based electrolyte leads to the formation of a thin and inorganic-rich solid electrolyte interphase (SEI) on the K⁺ -pre-intercalated Ti₃ C₂ T_x electrode, which is beneficial for interfacial stability and reaction kinetics. As a proof of concept, 3D K⁺ -Ti₃ C₂ T_x //activated carbon (AC) potassium-ion hybrid capacitors (PIHCs) were assembled, which exhibited promising electrochemical performances. These results highlight the significant roles of both rational structure design and electrolyte optimization for highly reactive MXene-based anode materials in energy storage devices.

Mechanistic Insights into the Structural Modulation of Transition Metal Selenides to Boost Potassium Ion Storage Stability

Atomic-level structure engineering is an effective strategy to reduce mechanical degradation and boost ion transport kinetics for battery anodes. To address the electrode failure induced by large ionic radius of K⁺ ions, herein we synthesized Mn-doped ZnSe with modulated electronic structure for potassium ion batteries (PIBs). State-of-the-art analytical techniques and theoretical calculations were conducted to probe crystalline structure changes, ion/electron migration pathways, and micromechanical stresses evolution mechanisms. We demonstrate that the heterogeneous adjustment of the electronic structure can relieve the potassiumization-induced internal strain and improve the structural stability of battery anodes. Our work highlights the importance of the correlation between doping chemistry and mechanical stability, inspiring a pathway of structural engineering strategy toward a highly stable PIBs.

A Low-Cost Na-Ion and K-Ion Batteries Using a Common Organic Cathode and Bismuth Anode

Molecule-aggregation organic electrodes in principle have the capability for "single-molecule-energy-storage" in metal-ion rechargeable batteries, which indicates that the same organic electrode can be simultaneously applied to multiple metal-ion rechargeable batteries. In this study, the polyanionic organic compound 9,10-anthraquinone-2,6-disulfonate (Na₂ AQ26DS, 130 mAh g^-1 ) is used as a common cathode and metal bismuth (Bi) as a common anode to simultaneously assemble low-cost Na-ion and K-ion full cells. The Na-ion full cells can deliver the peak discharge capacity of 139 mAh g^-1 _cathode at 0.5-3.0 V, and the K-ion full cells can show the peak discharge capacity of 130 mAh g^-1 _cathode at 0.5-3.0 V. These results are comparable to the best organic-based Na-ion and K-ion full cells reported to date.

Solid Solution of Bi and Sb for Robust Lithium Storage Enabled by Consecutive Alloying Reaction

Materials with alloying reactions have significant potential as electrodes for lithium-ion batteries (LIBs) due to its high theoretical capacity and appropriate lithiation potentials. Nonetheless, their cycling performance is inferior due to violent volume expansion and severe pulverization of active materials. Herein, solid solution of Bi_0.5 Sb_0.5 encapsulated with carbon is discovered to enable consecutive alloying reactions with manageable volume change, suitable for developing LIBs with high capacity and robust cyclability. A Sb-rich shell and Bi-rich core structure is formed in cycling since the alloying reaction between Sb and Li occurs first, followed by the alloying reaction between Bi and Li. Such a consecutive alloying reaction obeying the thermodynamic path is experimentally realized by the carbon capsulation, which acts as a protecting solid layer to avoid polarized reactions occurred when exposed directly to liquid electrolyte. The LIBs using Bi_0.5 Sb_0.5 @carbon run on the consecutive alloying reactions exhibits high capacity, prolonged lifespan (489.4 mAh g^-1 after 2000 cycles at 1 A g^-1 ) and fast kinetic, while those using bare Bi_0.5 Sb_0.5 suffer from worsened kinetic and thus a poor cycling performance owning to the polarized reactions. The work paves a way of developing alloy electrodes for alkaline-ion rechargeable batteries with potential industry applications.

Realizing Fast Diffusion Kinetics Based on Three-Dimensional Ordered Macroporous Cu9S5@C for Potassium-Ion Batteries

Recently, potassium-ion batteries (PIBs) have been deemed to be a potential next-generation energy storage system for large-scale application because of the similar metal-ion storage mechanism as lithium-ion batteries and rich potassium resources. However, the large-sized potassium ion will cause sluggish reaction kinetics of K⁺ during charge/discharge processes, hindering the development of high-performance PIBs. In this work, copper sulfide embedded in three-dimensional ordered macroporous carbon framework (3DOM Cu₉S₅@C) was prepared through a sulfidation and subsequent ion exchange strategy with 3D ordered macropore Zn-based metal-organic frameworks as a precursor for an advanced PIBs anode. In particular, the interconnected 3D ordered macroporous structure can provide rapid transport channels for the large potassium ions and create a sufficient contact area for solid electrode materials and the liquid electrolyte, which is conducive to improve the ionic diffusion kinetics of batteries. Consequently, when the prepared 3DOM Cu₉S₅@C composite was used as a PIBs anode material, it shows a remarkable potassium storage rate capacity of 170 mA h g^-1 at 2.0 A g^-1 and an excellent cycling stability of 316 mA h g^-1 at 100 mA g^-1 after 200 cycles.

Versatile Interfacial Self-Assembly of Ti3C2Tx MXene Based Composites with Enhanced Kinetics for Superior Lithium and Sodium Storage

Exploring nanostructured transition-metal sulfide anode materials with excellent electrical conductivity is the key point for high-performance alkali metal ion storage devices. Herein, we propose a powerful bottom-up strategy for the construction of a series of sandwich-structured materials by a rapid interfacial self-assembly approach. Oleylamine could act as a functional reagent to guarantee that the nanomaterials self-assemble with MXene. Benefiting from the small size of Co-NiS nanorods, excellent conductivity of MXene, and sandwiched structure of the composite, the Co-NiS/MXene composite could deliver a high discharge capacity of 911 mAh g^-1 at 0.1 A g^-1 for lithium-ion storage. After 200 cycles at 0.1 A g^-1, a high specific capacity of 1120 mAh g^-1 could be still remaining, indicating excellent cycling stability. For sodium-ion storage, the composite exhibits high specific capacity of 541 mAh g^-1 at 0.1 A g^-1 and excellent rate capability (263 mAh g^-1 at 5 A g^-1). This work offers a straightforward strategy to design and construct MXene-based anode nanomaterials with sandwiched structure for high-performance alkali metal ion storage and even in other fields.

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.

Alloyed BiSb Nanoparticles Confined in Tremella-Like Carbon Microspheres for Ultralong-Life Potassium Ion Batteries

Bismuth-antimony alloy is considered as a promising potassium ion battery anode because of its combination of the high theoretical capacity of antimony and the excellent rate capacity of bismuth. However, the large volume change and sluggish reaction kinetic upon cycling have triggered severe capacity fading and poor rate performance. Herein, a nanoconfined BiSb in tremella-like carbon microspheres (BiSb@TCS) are delicately designed to address these issues. As-prepared BiSb@TCS renders an outstanding potassium-storage performance with a reversible capacity of 181 mAh g^-1 after ultralong 5700 cycles at a current density of 2 A g^-1 , and an excellent rate capacity of 119.3 mAh g^-1 at 6 A g^-1 . Such a superior performance can be ascribed to the delicate microstructure. The self-assembled carbon microspheres can strengthen integral structure and effectively accommodate the volume expansion of BiSb nanoparticles, and 2D carbon nanowalls in carbon microspheres can provide fast ion/electron diffusion dynamic. Theoretical calculation also suggests a thermodynamic feasibility of alloyed BiSb nanoparticles for storing potassium ion. Such a work shows that BiSb@TCS possesses a great potential to be a high-performance anode of potassium ion batteries. The rational designing of multiscaled structure would be instructive to the exploitation of other energy-storage materials.