Tellurium: A High-Volumetric-Capacity Potassium-Ion Battery Electrode Material

Phenyl Tellurosulfides as Cathode Materials for Rechargeable Lithium Batteries

Phenyl ditelluride (PDTe) as a cathode material for rechargeable batteries has a low specific capacity (130.9 mAh g-1) due to limited active sites (two). To increase its capacity, additional active species need to be added to the structure of PDTe, like sulfur. Here, phenyl tellurosulfide (PDTeS) and phenyl tellurodisulfide (PDTeS2) can be formed via addition reactions and have specific capacities of 242.8 and 339.6 mAh g-1, respectively. The products are characterized by mass spectrometry and Raman spectroscopy. The Li/PDTeSn (n = 1-2) cells exhibit high material utilization (>85%) and unique redox mechanism. They can be cycled stably for more than 1000 cycles at an areal mass loading of 1.1 mg cm-2 and maintain capacity retentions of >72% after 100 cycles with PDTeSn loading of ∼6 mg cm-2. Moreover, the Li/PDTeS2 cell achieves a specific energy of up to 695 Wh kg-1 even when the electrolyte/PDTeS2 ratio is as low as 2.5 μL mg-1. The successful synthesis and application of PDTeSn prove that they are promising cathode materials for rechargeable lithium batteries.

Designer Anions for Better Rechargeable Lithium Batteries and Beyond

Non-aqueous electrolytes, generally consisting of metal salts and solvating media, are indispensable elements for building rechargeable batteries. As the major sources of ionic charges, the intrinsic characters of salt anions are of particular importance in determining the fundamental properties of bulk electrolyte, as well as the features of the resulting electrode-electrolyte interphases/interfaces. To cope with the increasing demand for better rechargeable batteries requested by emerging application domains, the structural design and modifications of salt anions are highly desired. Here, salt anions for lithium and other monovalent (e.g., sodium and potassium) and multivalent (e.g., magnesium, calcium, zinc, and aluminum) rechargeable batteries are outlined. Fundamental considerations on the design of salt anions are provided, particularly involving specific requirements imposed by different cell chemistries. Historical evolution and possible synthetic methodologies for metal salts with representative salt anions are reviewed. Recent advances in tailoring the anionic structures for rechargeable batteries are scrutinized, and due attention is paid to the paradigm shift from liquid to solid electrolytes, from intercalation to conversion/alloying-type electrodes, from lithium to other kinds of rechargeable batteries. The remaining challenges and key research directions in the development of robust salt anions are also discussed.

Carbon Nanofibers-Based Anodes for Potassium-Ion Battery

In recent years, with the global warming getting worse and increasing demand for energy, countries around the world are trying to develop new energy storage technologies to solve this problem. Currently, potassium-ion batteries (PIBs) have attracted tremendous attention from researchers as low-cost and high-performance energy storage devices. However, due to the huge ionic radius of K+, PIBs face significant volume expansion during cycling, which can easily lead to the collapse of electrode structures. In addition, the poor diffusion kinetics of K+ seriously affect the electrochemical performance of the battery. Carbon nanofibers (CNFs)-based materials (including CNFs, metal/CNFs composites, chalcogenide/CNFs composites, and other CNFs-based materials) are widely used as PIBs electrode anode materials due to their three-dimensional conductive network, heteroatom doping and excellent mechanical properties. This review discusses in detail the research progress of CNFs-based materials in PIBs, including material preparation, structural design, and performance optimization. On this basis, this article explores the key issues faced by CNFs-based materials and future development directions, and proposes improvement suggestions for providing new ideas for the development of CNFs-based materials.

-CoOTe ( = S, Se, and P) with Oxygen/Tellurium Dual Vacancies and Banana Stem Fiber-Derived Carbon Fiber s Battery-Type Cathode and Anode Materials for Asymmetric Supercapacitor

In this work, we demonstrated the synthesis of anions (X = selenium (Se), sulfur (S), and phosphorus (P)) doped cobalt oxytelluride (X-CoOTe) with oxygen and tellurium dual vacancies using hydrothermal methods, followed by selenization, sulfurization, and phosphorization reactions. Especially, the Se-CoOTe-modified nickel foam (Se-CoOTe/NF) electrode delivered a higher specific capacity (752.95 C/g) and an extremely lower charge transfer resistance (0.87 Ω) than S-CoOTe/NF and P-CoOTe/NF due to the higher metallic conductivity of Se. Both oxygen and tellurium vacancies facilitate higher charge transfer conductivity, specific capacity, and stability. On the other hand, banana stem core fiber-derived activated carbon fiber (AC) with exfoliated carbon sheet, cracked surface, and corresponding high surface area boosts the excellent cycle stability up to 4000 cycles with capacitance retention of 100.29%. Thus, the asymmetric device (Se-CoOTe/NF//AC/NF) exhibited an extendable cell voltage (1.55 V), higher energy density (155.6 W h kg-1) at a power density (1356.2 W kg-1), and generous long-term stability (100% retention up to 10 000 cycles) in a liquid alkaline electrolyte. In the practicability test, the proposed asymmetric device mutually showed an increased operating voltage from 1.55 to 4.65 V for a three-series connection. In a three-series connection, a single white LED and an LED string glowed efficiently. This new finding will be very useful to develop tellurium-based chalcogenides and biowaste-derived carbon for energy storage applications.

Efficient Polytelluride Anchoring for Ultralong-Life Potassium Storage: Combined Physical Barrier and Chemisorption in Nanogrid-in-Nanofiber

Metal tellurides (MTes) are highly attractive as promising anodes for high-performance potassium-ion batteries. The capacity attenuation of most reported MTe anodes is attributed to their poor electrical conductivity and large volume variation. The evolution mechanisms, dissolution properties, and corresponding manipulation strategies of intermediates (K-polytellurides, K-pTex) are rarely mentioned. Herein, we propose a novel structural engineering strategy to confine ultrafine CoTe2 nanodots in hierarchical nanogrid-in-nanofiber carbon substrates (CoTe2@NC@NSPCNFs) for smooth immobilization of K-pTex and highly reversible conversion of CoTe2 by manipulating the intense electrochemical reaction process. Various in situ/ex situ techniques and density functional theory calculations have been performed to clarify the formation, transformation, and dissolution of K-pTex (K5Te3 and K2Te), as well as verifying the robust physical barrier and the strong chemisorption of K5Te3 and K2Te on S, N co-doped dual-type carbon substrates. Additionally, the hierarchical nanogrid-in-nanofiber nanostructure increases the chemical anchoring sites for K-pTex, provides sufficient volume buffer space, and constructs highly interconnected conductive microcircuits, further propelling the battery reaction to new heights (3500 cycles at 2.0 A g-1). Furthermore, the full cells further demonstrate the potential for practical applications. This work provides new insights into manipulating K-pTex in the design of ultralong-cycling MTe anodes for advanced PIBs.

Rationally Designed ZnTe@C Nanowires with Superior Zinc Storage Performance for Aqueous Zn Batteries

Te-based materials with excellent electrical conductivity and ultra-high volume specific capacity have attracted much attention for the cost-efficient aqueous Zn batteries. However, the construction of functional structures with mild volume expansion and suppressed shuttle effects, enabling an expanded lifespan, is still a challenge for conversion-type materials. Herein, the carbon-coated zinc telluride nanowires (ZnTe@C NWs) are rationally designed as a high-performance cathode material for aqueous Zn batteries. The carbon-coated1D nanostructure could not only provide optimized transmission path for electrons and ions, but also help to maintain structure integrity upon volume variation and suppress intermediates dissolution, endowing the ZnTe@C NWs with improved cycling stability and reaction kinetics. Consequently, a reversible six-electron reaction mechanism of ZnTe@C NWs based on Te2- /Te4+ conversion with excellent output capacity (586 mAh g-1 at 0.1 A g-1 ) and lifespan (>250 mAh g-1 retained for 400 cycles at 1 A g-1 ) is eventually achieved.

Loss-free pulverization by confining copper oxide inside hierarchical nitrogen-doped carbon nanocages toward superb potassium-ion batteries

Taking the advantages of hierarchical nitrogen-doped carbon nanocages (hNCNCs) with nanocavities for encapsulation and multiscale micro-meso-macropores/high conductivity for mass/electron synergistic transportation, a conversion-type CuO anode material is confined inside hNCNCs for potassium storage. The so-obtained yolk-shelled CuO@hNCNC hybrids have tunable CuO contents in the range of 11.7-63.7 wt%. The unique architecture leads to the loss-free pulverization of the active components during charge/discharge, which increases the surface-controlled charge storage, shortens the K+ solid diffusion lengths with an enlarged K+ diffusion coefficient, and meanwhile enhances the rate capability and durability. Consequently, the optimized CuO@hNCNC delivers a high specific capacity of 498 mA h g-1 at 0.1 A g-1 and 194 mA h g-1 at 10.0 A g-1 based on the total mass of CuO@hNCNC, and a long-term stability. The capacity based on the CuO active component reaches a record-high 522 mA h g-1 at 1.0 A g-1 after 2000 cycles, which is ca. 2.5 times the state-of-the-art value in the literature. The evolution of the cycling performance with CuO loading is well understood based on the loss-free pulverization. This study demonstrates a new strategy to turn the generally harmful pulverization of active components into a beneficial factor for K+ storage, which paves the way for exploring high-performance anodes for rechargeable batteries.

Interfacial Tension-Impelled Self-Assembly and Morphology Tuning of Poly(3,4-ethylene dioxythiophene)/Tellurium Nanocomposites at Various Liquid/Liquid Interfaces

Compared to the enormous number of nanostructures that have been documented, the variety of nanostructures produced by organic polymerization is rather limited. We devised an unconventional route and a sustainable approach to distribute tellurium nanoparticles (Te NPs) in a poly(3,4-ethylene dioxythiophene) (PEDOT) matrix to form semiconducting organic-inorganic nanocomposites for potential applications in electrochemical sensing. The adopted strategy of in situ liquid/liquid interface-assisted polymerization aids in the formation of intimately tethered Te NPs on the PEDOT polymer chains, thereby preventing the aggregation of Te NPs. The untapped versatility inherent to using biphasic systems for interfacial polymerization is explored at three interface systems of immiscible solvents: chloroform/water, dichloromethane/water, and hexane/water, giving rise to PEDOT/Te nanocomposite (PTeNC) of distinct morphology. Chemical nature, crystallinity, and morphology investigations proved the successful formation of PTeNC in different interface systems. Consequently, the temporal evolution of interfacial tension in the preferential adsorption of nanoparticles and final product morphology was monitored by pendant drop tensiometry. Owing to the role of morphology, PTeNC synthesized at the hexane/water interface showcased the best electrocatalytic behavior toward nonenzymatic detection of l-ascorbic acid, an essential nutritional factor, and a neuromodulator with a limit of detection of 0.66 μM and excellent sensitivity, selectivity, and reproducibility. Hence, we envision that interface-assisted polymerization offers a nascent and robust strategy for encapsulating unusual electrode materials in polymeric matrices.

Low-temperature anode-free potassium metal batteries

In contrast to conventional batteries, anode-free configurations can extend cell-level energy densities closer to the theoretical limit. However, realizing alkali metal plating/stripping on a bare current collector with high reversibility is challenging, especially at low temperature, as an unstable solid-electrolyte interphase and uncontrolled dendrite growth occur more easily. Here, a low-temperature anode-free potassium (K) metal non-aqueous battery is reported. By introducing Si-O-based additives, namely polydimethylsiloxane, in a weak-solvation low-concentration electrolyte of 0.4 M potassium hexafluorophosphate in 1,2-dimethoxyethane, the in situ formed potassiophilic interface enables uniform K deposition, and offers K||Cu cells with an average K plating/stripping Coulombic efficiency of 99.80% at -40 °C. Consequently, anode-free Cu||prepotassiated 3,4,9,10-perylene-tetracarboxylicacid-dianhydride full batteries achieve stable cycling with a high specific energy of 152 Wh kg-1 based on the total mass of the negative and positive electrodes at 0.2 C (26 mA g-1) charge/discharge and -40 °C.

Biochar-Derived Hierarchical Porous Carbon as Tellurium Host for High-Performance Potassium-Tellurium Batteries

Potassium-ion battery is promising for its high abundance and low redox potential. As a conversion cathode, Te possesses high conductivity and theoretical volumetric capacity to couple with potassium. The stubborn issues of K-Te battery focus on the large volume change and rapid structure degradation of Te. Herein, we produce biomass carbon from mangosteen shell in a facile method, and obtain a hierarchical porous host with abundance of micropores and mesopores, which is obviously beneficial for hosting Te during K+ storage in K-Te battery. The specific capacity reach to 560 mAh g-1 in the initial cycle at 0.1 A g-1 , and remained 83.8 % after 200 cycles. Impressively, at a high current density of 2.0 A g-1 , the specific capacity still remained 62.6 % after 5000 cycle. These results endow such strategy an efficient way for the development of K-Te batteries.

3D ordered amorphous and porous TiO2 framework anode with low insertion barrier and fast kinetics for K-ion hybrid capacitors

TiO₂ is considered as a low cost, long-term stable, and safe anode for high power K-ion hybrid capacitors (KICs) due to its abundant reserve, small volume expansion rate, and sloping voltage plateau that avoids K-ion plating at high voltage polarization. However, the enhancement of its low capacity and sluggish kinetics caused by poor electroconductivity and high insertion barrier is still challenging to further develop high-performance KICs. Herein, the reduced graphene oxide (rGO) is embedded in the walls of 3D ordered macro-/mesoporous TiO₂ (termed as TiO₂@rGO framework) to create intimate TiO₂/rGO interfaces, ensuring the effectively electron transportation during potassiation/depotassiation of TiO₂ while maintaining rapid ions/electrolyte diffusion. Furthermore, the controlled amorphous TiO₂ framework can further lower the lattice insertion energies, contributing to a fast accommodation of K-ion. As expected, the amorphous TiO₂@rGO framework (TiO₂@rGO-1) exhibits a superior rate capability (148.8 mAh g^-1 at 5 A g^-1) and cycling stability (171.2 mAh g^-1 at 1 A g^-1 after 800 cycles). The assembled KICs can reach a high energy/power density of 125.2 Wh kg^-1/4267.4 W kg^-1 as well as a long-term lifespan. This tactic provides a reliable and general way to design a TiO₂-based anode with fast kinetics toward high-performance KICs.

Multilevel spatial confinement of transition metal selenides porous microcubes for efficient and stable potassium storage

Recently, potassium-ion batteries (PIBs) have been considered as one of the most promising energy storage systems; however, the slow kinetics and large volume variation induced by the large radius of potassium ions (K⁺) during chemical reactions lead to inferior structural stability and weak electrochemical activity for most potassium storage anodes. Herein, a multilevel space confinement strategy is proposed for developing zinc-cobalt bimetallic selenide (ZnSe/Co_0.85Se@NC@C@rGO) as high-efficient anodes for PIBs by in-situ carbonizing and subsequently selenizing the resorcinol-formaldehyde (RF)-coated zeolitic imidazolate framework-8/zeolitic imidazolate framework-67 (ZIF-8/ZIF-67) encapsulated into 2D graphene. The highly porous carbon microcubes derived from ZIF-8/ZIF-67 and carbon shell arising from RF provide rich channels for ion/electron transfer, present a rigid skeleton to ensure the structural stability, offer space for accommodating the volume change, and minimize the agglomeration of active material during the insertion/extraction of large-radius K⁺. In addition, the three-dimensional (3D) carbon network composed of graphene and RF-derived carbon-coated microcubes accelerates the electron/ion transfer rate and improves the electrochemical reaction kinetics of the material. As a result, the as-synthesized ZnSe/Co_0.85Se@NC@C@rGO as the anode of PIBs possesses the excellent rate capability of 203.9 mA h g^-1 at 5 A g^-1 and brilliant long-term cycling performance of 234 mA h g^-1 after 2,000 cycles at 2 A g^-1. Ex-situ X-ray diffraction (Ex-situ XRD) diffraction reveals that the intercalation/de-intercalation of K⁺ proceeds through the conversion-alloying reaction. The proposed strategy based on the spatial confinement engineering is highly effective to construct high-performance anodes for PIBs.

3D space-confined Co0.85Se architecture with effective interfacial stress relaxation as anode material reveals robust and highly loading potassium-ion batteries

Conversion-type transition metal chalcogenide anodes could bring relatively high specific capacity in potassium ion storage due to multiple electron transport reactions, but often accompanying huge volume changes and resulting in low cycle life and rapid capacity fading.While electrode materials are closely packed, the contact at the interface during potassiation/depotassiation is similar to point-to-point contact, generating strong stress to make self-aggregation occur. In this work, we constructed a 3D carbon framework to confine Co_0.85Se nanocrystals in three-dimensional space, both fulfilling the requirements of the material's size in the nano-scale and providing the largest contact area for releasing stress. With this optimization, nitrogen-doped carbon confined Co_0.85Se nanocrystals (Co_0.85Se@NC) reach an ultra-stable cycle life over 4000 times with a specific capacity of 190.9 mA h g^-1 at 500 mA g^-1 and provide 155.6 mA h g^-1 at 10 A g^-1 in the rate capability test. It also renders the areal capacity up to 1.03 mA h cm^-2 at 500 mA g^-1 in the high-mass loading test. Furthermore, based on the finite element analysis, the 3D confinement strategy has the lowest interfacial stress, ensuring Co_0.85Se nanocrystals with high structural integrity. This strategy can relieve the stress issue in the conversion-type anode and demonstrate superior electrochemical performance even at high-loading mass electrodes.

Defect-Enriched Hollow Porous Carbon Nanocages Enable Highly Efficient Chlorine Evolution Reaction

Metal-free carbon-based catalysts are crucial for the electrocatalytic chlorine evolution reaction (CER) to reduce the usage of noble metals and industrial cost. However, the corresponding catalytic activity of high overpotential and low durability hinders their wide application. Here, a hollow porous carbon (HPC) nanocage with a controlled oxygen electronic state around designed carbon defects for CER activity is reported. Alkali etching can bring defects in zeolite with a hollow structure. In a hard template strategy, the type of carbon defects is directly related to etching degree of the zeolite template. More importantly, the oxygen atoms can be "borrowed" from the zeolite framework by the defective carbon. The electron density around unsaturated O atoms can be decreased on the minor defects in carbon compared with that on large defects which is favorable for the adsorption of Cl^- . Consequently, the as-synthesized HPC nanocages with minor defects show excellent electrocatalytic performance for CER with a low overpotential of 94 mV at current density of 10 mA cm^-2 with good stability, which is superior to the commercial precious metal catalyst of dimensionally stable anode (DSA), and the best in the reported carbon materials. The designed carbon materials provide an option for metal-free industrial catalysts with significant CER activities.

Confined Assembly of Hydrated Vanadium Oxide into Hollow Mesoporous Carbon Nanospheres for Fast and Stable K+ Storage Capability

The rational structural design of the electrode materials is significant to enhance the electrochemical performance for potassium ion storage, benefiting from the shortened ion diffusion distance, increased conductivity, and pseudo-capacitance promotion. Herein, hydrated vanadium oxide (HVO) nanosheets with enriched oxygen defects are well confined into hollow mesoporous carbon spheres (HMCS), producing O_d -VOH@C nanospheres through one-step hydrothermal reaction. Attributed to the restricted growth in the HMCS, the HVO nanosheets are loosely packed, generating abundant interfacial boundaries and large specific areas. As a result, O_d -VOH@C nanospheres show increased reaction kinetics and well buffer the volume effects for the K⁺ storage. O_d -VOH@C delivers stable capacities of 138 mAh g^-1 at 2.0 A g^-1 over 10 000 cycles in half-cells attributed to the high pseudo-capacitance contribution. The K⁺ storage mechanism of insertion and conversion reaction is confirmed by ex situ X-ray diffraction, Raman, and X-ray photoelectron spectroscopy analyses. Moreover, the symmetric potassium-ion capacitors of O_d -VOH@C//O_d -VOH@C deliver a high energy density of 139.6 Wh kg^-1 at the power density of 948.3 W kg^-1 .

Working Aqueous Zn Metal Batteries at 100 °C

Reliable power supplies at extremely high temperatures are urgently needed to broaden the application scenarios for electric devices. Aqueous zinc metal batteries (ZMBs) with intrinsic safety are a promising alterative for high-temperature energy storage. However, the reversibility and long-term cycling stability of aqueous ZMBs at extremely high temperatures (≥100 °C) have rarely been explored. Herein, we reveal that spontaneous Zn corrosion and severe electrochemical hydrogen evolution at high temperature are vital restrictions for traditional aqueous ZMBs. To address this, a crowding agent, 1,5-pentanediol, was introduced into an aqueous electrolyte to suppress water reactivity by strengthening O-H bonds of H₂O and decreasing H₂O content in the Zn²⁺ solvation sheath, while maintaining flame resistance of the electrolyte. Importantly, this electrolyte enabled reversible Zn deposition with a Coulombic efficiency of 98.1% and a long cycling life of Zn//Zn batteries for over 500 cycles (at 1 mA cm^-2 and 0.5 mAh cm^-2) at 100 °C. Moreover, stable cycling of Zn//Te full batteries at 100 °C was demonstrated.

Flat-Zigzag Interface Design of Chalcogenide Heterostructure toward Ultralow Volume Expansion for High-Performance Potassium Storage

Heterostructure construction of layered metal chalcogenides can boost their alkali-metal storage performance, where the charge transfer kinetics can be promoted by the built-in electric fields. However, these heterostructures usually undergo interface separation due to severe layer expansion, especially for large-size potassium accommodation, resulting in the deconstruction of heterostructures and battery performance fading. Herein, first a stable interface design strategy where two metal chalcogenides with totally different layer-morphologies are stacked to form large K⁺ transport channels, rendering ultralow interlayer expansion, is presented. As a proof of concept, the flat-zigzag MoS₂ /Bi₂ S₃ heterostructures stacked with zigzag-morphology Bi₂ S₃ and flat-morphology MoS₂ present an ultralow expansion ratio (1.98%) versus MoS₂ (9.66%) and Bi₂ S₃ (9.61%), which deliver an ultrahigh potassium storage capacity of above 600 mAh g^-1 and capacity retention of 76% after 500 cycles, together with the built-in electric field of heterostructures. Once the heterostructures are used as an anode for potassium-based dual-ion batteries (K-DIBs), it achieves a superior full-cell capacity of ≈166 mAh g^-1 with a capacity retention of 71% after 400 cycles, which is an outstanding performance among the reported K-DIBs. This proposed interface stacking strategy may offer a new way toward stable heterostructure design for metal ions storage and transport applications.

Low-Temperature High-Areal-Capacity Rechargeable Potassium-Metal Batteries

High mass loading and high areal capacity are key metrics for commercial batteries, which are usually limited by the large charge-transfer impedance in thick electrodes. This can be kinetically deteriorated under low temperatures, and the realization of high-areal-capacity batteries in cold climates remains challenging. Herein, a low-temperature high-areal-capacity rechargeable potassium-tellurium (K-Te) battery is successfully fabricated by knocking down the kinetic barriers in the cathode and pairing it with stable anode. Specifically, the in situ electrochemical self-reconstruction of amorphous Cu_1.4 Te in a thick electrode is realized simply by coating micro-sized Te on the Cu collector, significantly improving its ionic conductivity. Meanwhile, the optimized electrolyte enables fast ion transportation and a stable K-metal anode at a large current density and areal capacity. Consequently, this K-Te battery achieves a high areal capacity of 1.25 mAh cm^-2 at -40 °C, which greatly exceeds those of most reported works. This work highlights the significance of electrode design and electrolyte engineering for high areal capacity at low temperatures, and represents a critical step toward practical applications of low-temperature batteries.

Amorphous Tellurium-Embedded Hierarchical Porous Carbon Nanofibers as High-Rate and Long-Life Electrodes for Potassium-Ion Batteries

Tellurium (Te) is a promising electrode active material for potassium-ion batteries due to its intrinsic electrical conductivity and ultra-high theoretical volumetric capacity. Nevertheless, Te-based electrodes usually exhibit low capacity at high rates and poor cycling stability caused by the large volume expansion and severe polytellurides dissolution. Herein, hierarchical porous carbon nanofibers (HPCNFs) film is utilized as a multifunctional Te substrate. The free-standing Te@HPCNFs electrode renders an outstanding K-ion storage performance with a high-rate capacity of 1294.4 mAh cm^-3 (207.1 mAh g^-1 _Te ) at 14C and ultra-long lifespan for 4500 cycles at 7C, and K-ion full batteries coupled with KSn alloy anode also exhibit good cyclability. Such a superior performance benefits from the space confinement of HPCNFs to load amorphous Te in the micropores for accommodating the volume change, where the interconnected conductive frameworks and residual hierarchical pores enable fast ion/electron diffusion kinetics. In situ UV-vis absorption spectra confirm that the detachment of polytellurides and K₂ Te from the electrode is effectively suppressed, and ex situ X-ray photoelectron spectroscopy analysis reveals the conversion of Te into K₅ Te₃ and K₂ Te. This work presents the significance of porous structure design of carbon matrix to construct high performance Te electrodes, which will be instructive for chalcogens-based energy-storage materials.

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.

Tellurium: A High-Performance Cathode for Magnesium Ion Batteries Based on a Conversion Mechanism

Magnesium ion batteries (MIBs), due to the low redox potential of Mg, high theoretical capacity, dendrite-free magnesiation, and safe nature, have been recognized as a post-lithium energy storage system. However, an ongoing challenge, sluggish Mg²⁺ kinetics in the small number of available cathode materials of MIBs, restricts its further development. The existing cathodes mostly deliver unsatisfactory capacity with poor cycling life based on the traditional ion-intercalation mechanism. Herein, we fabricated a conversion-type Mg∥Te battery based on a reversible two-step conversion reaction (Te to MgTe₂ to MgTe). High discharge capacities (387 mAh g^-1) and rate capability (165 mAh g^-1 at 5 A g^-1) can be achieved. The diffusivity of Mg²⁺ can reach 3.54 × 10^-8 cm² s^-1, enabled by the high electrical conductivity of Te and increased surface conversion sites. Subsequently, ab initio molecular dynamics simulation was also carried out to further confirm the conversion mechanism and fast Mg²⁺ transportation kinetics.

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.

High-Performance Potassium-Tellurium Batteries Stabilized by Interface Engineering

The emerging potassium-tellurium (K-Te) battery system is expected to realize fast reaction kinetics and excellent rate performance due to the exceptional electrical conductivity of Te. However, there has been a lack of fundamental knowledge about this new K-Te system, including the reaction mechanism and cathode structure design. Herein, a two-step reaction pathway from Te to K₂ Te₃ and ultimately to K₅ Te₃ is investigated in carbonate electrolyte-based K-Te batteries by X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction characterizations. Additionally, the atomic layer deposition technique is adopted to deposit an ultrathin aluminum oxide (Al₂ O₃ ) film on the electrode surface, which induces the generation of a stable solid electrolyte interphase layer and reduces the loss of active materials effectively. Consequently, the rationally fabricated Te/porous carbon cathode with functional Al₂ O₃ coating delivers remarkable long-term cycling stability over 500 cycles at 1 C with an ultralow capacity decay of only 0.01% per cycle. This interface engineering strategy is validated to stabilize the electrode surface, enhance the structural integrity and ensure reliable electron transfer and K-ion conduction over repeated potassiation/depotassiation cycles. These findings are expected to promote the development of high-energy-density K-S/Se/Te batteries.

Toward Theoretical Capacity and Superhigh Power Density for Potassium-Selenium Batteries via Facilitating Reversible Potassiation Kinetics

Potassium-selenium (K-Se) batteries attract tremendous attention because of the two-electron transfer of the selenium cathode. Nonetheless, practical K-Se cells normally display selenium underutilization and unsatisfactory rate capability. Herein, we employ a synergistic spatial confinement and architecture engineering strategy to establish selenium cathodes for probing the effect of K⁺ diffusion kinetics on K-Se battery performance and improving the charge transfer efficiency at ultrahigh rates. By impregnating selenium into hollow and solid carbon spheres with similar diameters and porous structures, the obtained parallel Se/C composites possess nearly identical selenium loadings, molecular structures, and heterogeneous interfaces but enormously different paths for K⁺ diffusion. Remarkably, as the solid-state K⁺ diffusion distance is significantly reduced, the K-Se cell achieves 96% of 2e^- transfer capacity (647.1 mA h g^-1). Reversible capacities of 283.5 and 224.1 mA h g^-1 are obtained at 7.5 and 15C, respectively, corresponding to an unprecedented high power density of 8777.8 W kg^-1. Quantitative kinetic analysis demonstrated a twofold higher capacitive charge storage contribution and a 1 order of magnitude higher K⁺ diffusion coefficient due to the short K⁺ diffusion path. By combining the determination of potassiation products by ex situ characterization and density functional theory (DFT) calculations, it is identified that the kinetic factor is decisive for K-Se battery performances.

Polyacrylonitrile-Reinforced Composite Gel Polymer Electrolytes for Stable Potassium Metal Anodes

The potassium-ion battery (PIB) is an emerging energy storage technology due to its potential low cost and reasonably high energy density. However, PIB suffers from severe potassium (K) dendrites growth and even short circuiting caused by the high reactivity of K metal. To address these challenges, this work develops a robust composite gel polymer electrolyte (CGPE), named poly(vinylidene fluoride-hexafluoropropylene) potassium bis(fluorosulfonyl)imide polyacrylonitrile (PVDF-HFP-KFSI@PAN). It is found that the introduction of PAN nanofibers not only improves the mechanical properties but also widens the electrochemical stability window of the CGPE. As a result, the CGPE is much more effective in regulating K stripping/plating and enabling stable K metal anode. K metal symmetrical cells with CGPE exhibit a lifetime of over 1200 h at the current density of 0.5 mA cm^-2 , in contrast to 22 h for PVDF-HFP-KFSI and 185 h for a conventional glass fiber separator. The main reasons for the excellent performance of K metal cells with CGPE are attributed to the suppressed K dendrite growth, good structural integrity electrochemical stability of the CGPE, and stable KF-rich solid electrolyte interphase layer at the electrode-CGPE interface. It is expected that this facile strategy to stabilize K metal will pave the way for safer and more durable K metal batteries.

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.

Design Principles of Sodium/Potassium Protection Layer for High-Power High-Energy Sodium/Potassium-Metal Batteries in Carbonate Electrolytes: a Case Study of Na2 Te/K2 Te

The sodium (potassium)-metal anodes combine low-cost, high theoretical capacity, and high energy density, demonstrating promising application in sodium (potassium)-metal batteries. However, the dendrites' growth on the surface of Na (K) has impeded their practical application. Herein, density functional theory (DFT) results predict Na₂ Te/K₂ Te is beneficial for Na⁺ /K⁺ transport and can effectively suppress the formation of the dendrites because of low Na⁺ /K⁺ migration energy barrier and ultrahigh Na⁺ /K⁺ diffusion coefficient of 3.7 × 10^-10 cm² s^-1 /1.6 × 10^-10 cm² s^-1 (300 K), respectively. Then a Na₂ Te protection layer is prepared by directly painting the nanosized Te powder onto the sodium-metal surface. The Na@Na₂ Te anode can last for 700 h in low-cost carbonate electrolytes (1 mA cm^-2 , 1 mAh cm^-2 ), and the corresponding Na₃ V₂ (PO₄ )₃ //Na@Na₂ Te full cell exhibits high energy density of 223 Wh kg^-1 at an unprecedented power density of 29687 W kg^-1 as well as an ultrahigh capacity retention of 93% after 3000 cycles at 20 C. Besides, the K@K₂ Te-based potassium-metal full battery also demonstrates high power density of 20 577 W kg^-1 with energy density of 154 Wh kg^-1 . This work opens up a new and promising avenue to stabilize sodium (potassium)-metal anodes with simple and low-cost interfacial layers.

Orthorhombic Cobalt Ditelluride with Te Vacancy Defects Anchoring on Elastic MXene Enables Efficient Potassium-Ion Storage

The fast and reversible potassiation/depotassiation of anode materials remains an elusive yet intriguing goal. Herein, a class of the P-doping-induced orthorhombic CoTe₂ nanowires with Te vacancy defects supported on MXene (o-P-CoTe₂ /MXene) is designed and prepared, taking advantage of the synergistic effects of the conductive o-P-CoTe₂ arrays with rich Te vacancy defects and the elastic MXene sheets with self-autoadjustable function. Consequently, the o-P-CoTe₂ /MXene superstructure exhibits boosted potassium-storage performance, in terms of high reversible capacity (373.7 mAh g^-1 at 0.2 A g^-1 after 200 cycles), remarkable rate capability (168.2 mAh g^-1 at 20 A g^-1 ), and outstanding long-term cyclability (0.011% capacity decay per cycle over 2000 cycles at 2 A g^-1 ), representing the best performance in transition-metal-dichalcogenides-based anodes to date. Impressively, the flexible full battery with o-P-CoTe₂ /MXene anode achieves a satisfying energy density of 275 Wh kg^-1 and high bending stability. The kinetics analysis and first-principles calculations reveal superior pseudocapacitive property, high electronic conductivity, and favorable K⁺ ion adsorption and diffusion capability, corroborating fast K⁺ ion storage. Especially, ex situ characterizations confirm o-P-CoTe₂ /MXene undergoes reversible evolutions of initially proceeding with the K⁺ ion insertion, followed by the conversion reaction mechanism.

Self-assembly of carbon nanotubes on a hollow carbon polyhedron to enhance the potassium storage cycling stability of metal organic framework-derived metallic selenide anodes

Potassium-ion batteries (PIBs) is increasingly studied because of their suitable redox potential and high natural abundance. However, potential anode materials with long-term cycling stability are still in high demand because of the large radius of K⁺. Herein, an MOF-derived hierarchical carbon structure and the self-assembly of CNTs on hollow carbon polyhedrons are used as carbon matrices to disperse and stabilize metal selenides(Co-Se@CNNCP). When the hybrid is utilized in PIBs, it displays a specific capacity of 410 mA h g^-1 at 0.1 A g^-1 after 80 cycles and 253 mA h g^-1 at 0.5 A g^-1 after 200 cycles with a capacity retention of 100%, while the metal selenides dispersed on hollow carbon polyhedrons without CNTs (Zn-Co-Se@NCP) lose 86% of their capacity after 200 cycles. The superior cycling stability of the hybrid is mainly attributed to the large amounts of CNTs suppressing the agglomeration of the metal selenide nanoparticles on the surface, and the hollow carbon polyhedrons cause a high structural integrity during the repreated K⁺ insertion and extraction process. This work offers a feasible route to design a hierarchical carbon matrix for use as the anode materials of PIBs with long-term cycling stability.

Enhanced Potassium Storage Performance for K-Te Batteries via Electrode Design and Electrolyte Salt Chemistry

Potassium batteries are an emerging energy storage technology due to the large abundance of potassium, low cost, and potentially high energy density. However, it remains challenging to find suitable electrode materials with high energy density and good cycling stability due to the structural instability and kinetics issues resulting from large size K⁺. Herein, a durable and high-capacity K-Te battery was developed by rational design of a Te/C electrode and electrolyte salt chemistry. A well-confined Te/C cathode structure was prepared by using a commercially available activated carbon as the Te host via a melt-diffusion method. Compared to bulky Te, the confined Te/C electrode exhibited greatly improved cycling stability, specific capacity, and rate capability in K-Te batteries. Moreover, it was found that the electrolyte salts (KPF₆ and KFSI) had significant impacts on the electrochemical performance of K-Te batteries. The Te/C electrode in the KPF₆-based carbonate electrolyte exhibited higher specific capacity and better rate performance than the Te/C electrode in the KFSI-based one. Mechanism studies revealed that the KPF₆ salt resulted in an organic species-rich solid-electrolyte interphase (SEI) on the Te/C electrode, allowing for fast electron transfer and K-ion diffusion and enhanced K-ion storage performance in K-Te batteries. In contrast, KFSI salt led to the formation of KF-rich SEI layers, which had much higher resistances for electron and K-ion transport and was less effective for the well-confined Te/C electrode. Our work finds that the Te electrode and electrolyte chemistry need to be simultaneously optimized and tailored toward K-ion storage in K-Te batteries. It is expected that the finding reported herein might be inspirable for the future development of K-chalcogen (S/Se/Te) batteries.

Red phosphorus embedded in TiO2/C nanofibers to enhance the potassium-ion storage performance

TiO₂-red phosphorus/C nanofibers (TiO₂-RP/CN) have been synthesized via electrospinning and then annealed with red phosphorus sublimation. Benefiting from the high electronic/ionic conductivity and robust stability of the unique structure, the TiO₂-RP/CN show high reversible capacities, as well as an outstanding cycling ability. In K half cells, the capacity decay of the TiO₂-RP/CN electrode mainly occurs in the first few cycles, and at 0.05 A g^-1 it delivers a high specific capacity of 257.8 mA h g^-1 after 500 cycles. K full cells were fabricated; these are well-matched with PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride) and also exhibited a good electrochemical performance (62 mA h g^-1 after 100 cycles). Therefore, the TiO₂-RP/CN are potential anode materials for use in K-ion batteries.

Advanced High-Performance Potassium-Chalcogen (S, Se, Te) Batteries

Current great progress on potassium-chalcogen (S, Se, Te) batteries within much potential to become promising energy storage systems opens a new avenue for the rapid development of potassium batteries as a complementary option to lithium ion batteries. The discussion mainly concentrates on recent research advances of potassium-chalcogen (S, Se, Te) batteries and their corresponding cathode materials in this review. Initially, the development of cathode materials for four types of batteries is introduced, including: potassium-sulfur (K-S), potassium-selenium (K-Se), potassium-selenium sulfide (K-Se_x S_y ), and potassium-tellurium (K-Te) batteries. Next, critical challenges for chalcogen-based electrodes in devices operation are summarized. In addition, some pragmatic strategies are proposed as well to relieve the low electronic conductivity, large volumetric expansion, shuttle effect, and potassium dendrite growth. At last, the perspectives on designing advanced cathode materials for potassium-chalcogen batteries are provided with the goal of developing high-performance potassium storage devices.

Boosting Potassium Storage by Integration Advantageous of Defect Engineering and Spatial Confinement: A Case Study of Sb2 Se3

The potassium ion batteries (KIBs) based on conversion/alloying reaction mechanisms show high theoretical capacity. However, their applications are hampered by the poor cyclability resulting from the inherent large volume variations and the sluggish kinetics during K⁺ repeated insertion/extraction process. Herein, taken Sb₂ Se₃ as a model material, by rational design, nickel doped-carbon coated Sb₂ Se₃ nanorods (denoted as (Sb_0.99 Ni_0.01 )₂ Se₃ @C) are prepared through combined strategies of the conductive encapsulation and crystal structure modification. The carbon coating acts as an efficient buffer layer that maintains superior structural stability upon cycling. The introduction of Ni atoms can enhance electrical conductivity, leading to outstanding rate performance, which are confirmed by density functional theory calculation. The (Sb_0.99 Ni_0.01 )₂ Se₃ @C displays excellent reversible capacity (410 mAh g^-1 at 0.1 A g^-1 after 100 cycles) and unprecedented rate capability (140 mAh g^-1 at 10 A g^-1 ). Furthermore, KFeHCF//(Sb_0.99 Ni_0.01 )₂ Se₃ @C full cell exhibits a high specific capacity (408 mAh g^-1 at 0.1 A g^-1 ), superior rate capability (260 mAh g^-1 at 2 A g^-1 ). This work can open up a new avenue for the design of stable conversion/alloying-based anodes for high energy density KIBs.

In Situ Confined Co5Ge3 Alloy Nanoparticles in Nitrogen-Doped Carbon Nanotubes for Boosting Lithium Storage

Ge-based materials have garnered much attention in lithium-ion batteries (LIBs) for their high theoretical capacity, but these materials suffer from huge volume changes and serious pulverization, which cause insufficient lithium storage performance. Herein, a composite composed of Co₅Ge₃- and nitrogen-doped carbon nanotube (Co₅Ge₃/N-CNT) was successfully synthesized using ZIF-67 and GeO₂ as precursors. There are interactions between the Co₅Ge₃ alloy nanoparticles and carbon nanotubes in the growth process, in which the Co₅Ge₃ alloy nanoparticles were confined in situ in N-CNTs and the in situ growth of N-CNTs was boosted in the existence of the Co₅Ge₃ catalyst. Density functional theory calculations revealed that the electronic conductivity of the Co₅Ge₃ alloy is much higher than that of Ge and the Li⁺ interaction energy of the former is lower than that of the latter. In addition, the interconnected carbon nanotubes not only offer Li⁺ diffusion pathways and electronic networks but also increase electronic conductivity. Importantly, carbon nanotubes and Co metal have a synergistic effect of buffering volume charge of Ge in the process of Li⁺ intercalation/deintercalation. As expected, the Co₅Ge₃/N-CNT composite demonstrated a high reversible capacity of 853.7 mA h g^-1 at 2 A g^-1 after 1500 cycles and attractive rate performance of up to 10 A g^-1.

Realizing Few-Layer Iodinene for High-Rate Sodium-Ion Batteries

Elemental 2D materials with fascinating characteristics are regarded as an influential portion of the 2D family. Iodine is as a typical monoelemental molecular crystal and exhibits great prospects of applications. To realize 2D iodine, not only is it required to separate the weak interlayer van der Waals interactions, but also to reserve the weak intramolecular halogen bonds; thus, 2D iodine is still unexploited until now. Herein, atomically thin iodine nanosheets (termed "iodinene") with the thickness around 1.0 nm and lateral sizes up to hundreds of nanometers are successfully fabricated by a liquid-phase exfoliation strategy. When used for the cathode of rechargeable sodium-ion batteries, the ultrathin iodinene exhibits superb rate properties with a high specific capacity of 109.5 mA h g^-1 at the high rate of 10 A g^-1 owing to its unique 2D ultrathin architecture with remarkably enhanced pseudocapacitive behavior. First-principles calculations reveal that the diffusion of sodium ions in few-layered iodinene changes from the original horizontal direction in bulk to the vertical with a small energy barrier of 0.07 eV because of the size effect. The successful preparation and intensive structural investigation of iodinene paves the way for the development of novel iodine-based science and technologies.

Aqueous Zinc-Tellurium Batteries with Ultraflat Discharge Plateau and High Volumetric Capacity

Traditional aqueous zinc-ion batteries (ZIBs) based on ion-intercalation or surface redox behaviors at the cathode side suffer severely from an unsatisfactory specific capacity and unstable output potential. Herein, these issues are applied to a conversion-type zinc-tellurium (Zn-Te) battery. Typically, this battery works based on a two-step solid-to-solid conversion with the successive formation of zinc ditelluride (ZnTe₂ ) and zinc telluride (ZnTe). It delivers an ultrahigh volumetric capacity of 2619 mAh cm^-3 (419 mAh g^-1 ), 74.1% of which is from the first conversion (Te to ZnTe₂ ) with an ultraflat discharge plateau. Though reported first in a challenging aqueous environment, this Zn-Te battery demonstrates an excellent capacity retention of >82.8% after 500 cycles, which results from the elimination of the notorious "shuttle effect" due to the solid-to-solid conversion behaviors. In addition, a quasi-solid-state Zn-Te battery is also fabricated, exhibiting superior flexibility, robustness, and good electrochemical performance. This work develops a novel cathode material based on conversion-type ion-storage mechanism. The system is attractive due to its ultrastable energy output, which is rarely reported for ZIBs.