Potassium-ion Batteries Research Articles

Tailoring Stress-Relieved Structure for SnSe Toward High Performance Potassium Ion Batteries.

Metal chalcogenides as an ideal family of anode materials demonstrate a high theoretical specific capacity for potassium ion batteries (PIBs), but the huge volume variance and poor cyclic stability hinder their practical applications. In this study, a design of a stress self-adaptive structure with ultrafine SnSe nanoparticles embedded in carbon nanofiber (SnSe@CNF) via the electrospinning technology is presented. Such an architecture delivers a record high specific capacity (272 mAh g-1 at 50mA g-1) and high-rate performance (125 mAh g-1 at 1 A g-1) as a PIB anode. It is decoded that the fundamental understanding for this great performance is that the ultrafine SnSe particles enhance the full utilization of the active material and achieve stress relief as the stored strain energy from cycling is insufficient to drive crack propagation and thus alleviates the intrinsic chemo-mechanical degradation of metal chalcogenides.

Alleviated mechanical structure decay and accelerated transport kinetics via KNCHCF@NiHCF core–shell structure for aqueous potassium-ion batteries

The sluggish ion transport and mechanical decay caused by K+ intercalation can hinder the K+ storage ability of Prussian blue analogs (PBAs), potential cathode materials for potassium-ion batteries (PIBs). The construction of composite materials using adjustable chemical components of PB is an effective method to improve cycling stability. In this study, a core–shell structure of KNiCoFe(CN)6@NiFe(CN)6 (KNCHCF@NiHCF) was prepared to utilize the inertness of Ni2+ and the stability of Fe–CN–Ni bonds and enhance the performance of PBAs. Different concentrations of NiHCF coating (Ni-0, Ni-2, Ni-5, and Ni-60) were introduced into the outer layer of KNCHCF using a simple solution precipitation method. The aforementioned core–shell structure and the corresponding built-in electric field enhanced the structural stability and K+/e− transport kinetics of the fabricated materials. And Ni-5 exhibited the best electrochemical performance with excellent durable cycling stability and rate performance. Furthermore, the reversible single-phase insertion and extraction reaction of K+ storage mechanism within the Ni-5 cathode was revealed using ex-/in-situ characterization techniques. This strategy may facilitate the development of other cathode materials for rechargeable metal ion batteries.

Effects of cation substitution effects of dicarboxylic acid for energy storage applications

Organic materials (OMs) can accept alkali ions and function as energy storage systems, displaying several advantages such as low cost, ease of synthesis, and utilization of recyclable materials. Owing to their higher theoretical capacity, OMs exhibit a higher energy density, cheaper price, and easy recover than those of inorganic materials such as graphite, silicon, and metal oxides, respectively. This study reports the use of potassium 4-oxo-4H-pyran-2,6-dicarboxylic acid (K2CDA) and potassium 4-oxo-4H-pyran-2,6-dicarboxylic acid (K2CDO) as anode materials for potassium-ion batteries (KIBs) and lithium-ion batteries (LIBs). Although they share similar lightweight, carbonyl, and carboxylate functional groups, both materials display distinct reaction behaviors owing to differences in electronegative heteroatoms N and O. In this study, two alkaline salts (KFSI and LiFSI) have been discussed on the substitution effect of doping/ de-doping processes. K2CDA and K2CDO. Consequently, after 200 cycles, the K2CDA anodes deliver capacities of 310 (KFSI) and 485 (LiFSI) mAh g−1, respectively, at 0.1 C. The larger size of K+ compared with Li+ negatively impacts the performance of K2CDA. A similar trend is observed in the case of K2CDO in capacities of 220 (KFSI) and 405 mAh g‒1 (LiFSI), with 1.5 and 2.86 K+ ions participated in the corresponding redox reactions on the Fourier-transfer infrared spectroscopy analysis. The presence of N‒H in the K2CDA structure contributes to its superior performance and rate capability compared with K2CDO. In addition to the cation effect, the structural differences between K2CDA and K2CDO also influence their electrochemical activity.

Nonflammable Phosphate‐Based Electrolyte for Safe and Stable Potassium Batteries Enabled by Optimized Solvation Effect

AbstractCurrent potassium‐ion batteries (PIBs) are limited in safety and lifetime owing to the lack of suitable electrolyte solutions. To address these issues, herein, we report an innovative non‐flammable electrolyte design strategy that leverages an optimal moderate solvation phosphate‐based solvent which strikes a balance between solvation capability and salt dissociation ability, leading to superior electrochemical performance. The formulated electrolyte simultaneously exhibits the advantages of low salt concentration (only 0.6 M), low viscosity, high ionic conductivity, high oxidative stability, and safety. Our electrolyte also promotes the formation of self‐limiting inorganic‐rich interphases at the anode surface, alongside robust cathode‐electrolyte interphase on iron‐based Prussian blue analogues, mitigating electrode/electrolyte side reactions and preventing Fe dissolution. Notably, the PIBs employing our electrolyte exhibit exceptional durability, with 80 % capacity retention after 2,000 cycles at high‐voltage of 4.2 V in a coin cell. Impressively, in a larger scale pouch cell, it maintains over 81 % of its initial capacity after 1,400 cycles at 1 C‐rate with high average Coulombic efficiency of 99.6 %. This work represents a significant advancement toward the realization of safe, sustainable, and high‐performance PIBs.

Nonflammable Phosphate-Based Electrolyte for Safe and Stable Potassium Batteries Enabled by Optimized Solvation Effect.

Current potassium-ion batteries (PIBs) are limited in safety and lifetime owing to the lack of suitable electrolyte solutions. To address these issues, herein, we report an innovative non-flammable electrolyte design strategy that leverages an optimal moderate solvation phosphate-based solvent which strikes a balance between solvation capability and salt dissociation ability, leading to superior electrochemical performance. The formulated electrolyte simultaneously exhibits the advantages of low salt concentration (only 0.6 M), low viscosity, high ionic conductivity, high oxidative stability, and safety. Our electrolyte also promotes the formation of self-limiting inorganic-rich interphases at the anode surface, alongside robust cathode-electrolyte interphase on iron-based Prussian blue analogues, mitigating electrode/electrolyte side reactions and preventing Fe dissolution. Notably, the PIBs employing our electrolyte exhibit exceptional durability, with 80 % capacity retention after 2,000 cycles at high-voltage of 4.2 V in a coin cell. Impressively, in a larger scale pouch cell, it maintains over 81 % of its initial capacity after 1,400 cycles at 1 C-rate with high average Coulombic efficiency of 99.6 %. This work represents a significant advancement toward the realization of safe, sustainable, and high-performance PIBs.

Highly-Solvating Electrolyte Enables Mechanically Stable and Inorganic-Rich Cathode Electrolyte Interphase for High-Performing Potassium-Ion Batteries.

Cathode-electrolyte interphase (CEI) is crucial for the reversibility of rechargeable batteries, yet receives less attention compared to solid-electrolyte interphase (SEI). The prevalent weakly-solvating electrolyte is usually proposed from the standing point of obtaining robust SEI, however, the resultant weak ion-solvent interaction gives rise to excessive free solvents and forms thick CEI with high kinetic barriers, which is disadvantageous for interfacial stability at the high working voltage. Herein, a highly-solvating electrolyte is reported to immobilize free solvents by generating stable ternary complexes and facilitate the growth of homogeneous and ultrathin CEI to boost the electrochemical performances of potassium-ion batteries (PIBs). Through time-of-flight secondary ion mass spectrometry and cryogenic transmission electron microscopy, It is revealed that the deliberately coordinated complexes are the key to forming mechanically stable and inorganic-rich CEI with superior diffusion kinetics for high-performing PIBs. Coupling with a K0.5MnO2 cathode and a soft carbon (SC) anode, a high energy density (202.3Whkg-1) is achieved with an exceptional cycle lifespan (92.5% capacity retention after 500 cycles) in a SC||K0.5MnO2 full cell, setting new performance benchmarks for PIBs.

Structure-modulation of flower-like VS2 via ammonium ion intercalation for high performance potassium-ion batteries

Transition vanadium sulfide is a promising anode material for potassium-ion batteries (PIBs), but the volume variation during charge-discharge cycling and low electric conductivity seriously hinder its applications. Herein, we designed a multilayer lamellar self-assembled flower-like vanadium sulfide with ammonium ion intercalation (VS2–NF) by a facile and inexpensive hydrothermal method to improve its electrochemical potassium ion storage performance. By introducing ammonia during the hydrothermal synthesis process, the structures of vanadium sulfide transformed to nanoflowers composed by ultrathin nanosheets from the initial nanosphere structures. The intercalation of ammonium ion enlarges the lattice fringes and induces anisotropic growth of vanadium sulfide, resulting in a large number of mesopores and increased specific surface area as well as the reactive sites of vanadium sulfide, which contribute to the enhanced potassium ion storage performance. Consequently, the structure-modulated VS2–NF exhibits a high specific capacity of 507 mAh g−1 after 50 cycles at a current density of 100 mA g−1. This approach provides a new routine for the modification of other transition metal disulfides as anode materials for PIBs.

Conductive layer coupled mesoporous hard carbon enabling high rate and initial Coulombic efficiency for potassium ion battery

Hard carbon with rich mesopores is considered as one of the most promising anodes for potassium-ion batteries, resulting from its shortened ions diffusion distance, good electrolyte penetration ability, and highly released stress. However, the well-developed pore channels tend to separate graphite-domains and enlarge direct contact area between electrode/electrolyte, which easily cause discontinuous electrons transfer paths and extra electrolyte depletion, thus leading to poor rate performance and initial Coulombic efficiency (ICE). Hence, we propose polyaniline conductive layer coated hollow mesoporous carbon spheres (HMCS@PAN) tailored based on local protonation reaction strategy, which can enhance conductivity and simultaneously maintain considerable pore structure, accounting for an ultrahigh-rate performance (233.9 mAh/g at 5 A/g) and long cycling life (216.8 mAh/g at 5 A/g over 2000 cycles). Besides, PAN coating can inhibit the direct contact between inner pore channels and electrolyte and reduce the excessive depletion of active ions in the filling of pores with larger pore size, which is conducive to building an even, stable, and inorganic-rich solid electrolyte interphase (SEI) layer, resulting in an excellent ICE (70.7%). This work provides a guidance for the structure design of mesopore hard carbon to improve its rate and ICE.

Fluorinated Surface Engineering towards High-rate and Durable Potassium-ion Battery.

Solid electrolyte interphase (SEI) crucially affects the rate performance and cycling lifespan, yet to date more extensive research is still needed in potassium-ion batteries. We report an ultra-thin and KF-enriched SEI triggered by tuned fluorinated surface design in electrode. Our results reveal that fluorination engineering alters the interfacial chemical environment to facilitate inherited electronic conductivity, enhance adsorption ability of potassium, induce localized surface polarization to guide electrolyte decomposition behavior for SEI formation, and especially, enrich the KF crystals in SEI by self-sacrifice from C-F bond cleavage. Hence, the regulated fluorinated electrode with generated ultra-thin, uniform, and KF-enriched SEI shows improved capacity of 439.3 mAh g-1 (3.82 mAh cm--2), boosted rate performance (202.3 mAh g-1 at 8.70 mA cm-2) and durable cycling performance (even under high loading of ~8.7 mg cm-2). We expect this practical engineering principle to open up new opportunities for upgrading the development of potassium-ion batteries.

Novel NASICON-type Mn0.5Ti2(PO4)3@F-doped carbon composite with high electrochemical performance as anode materials for potassium-ion batteries

Mn0.5Ti2(PO4)3 with a NASICON structural is used as an anode material in potassium-ion batteries due to its abundance of vacancies that can hold potassium ions. This characteristic not only contributes to its excellent stability but also results in a high specific capacity. However, the poor electrical conductivity of the polyanionic type structure limits the material's ability to fully utilize its capacity. In this paper, the conductivity and electrochemical stability of the Mn0.5Ti2(PO4)3 anode material are enhanced through composite formation with an F-doped carbon layer. The introduction of F into the carbon matrix creates a large number of vacancy defects and F active sites. The vacancies enhance the transport of potassium ions on the Mn0.5Ti2(PO4)3 material's surface, while the active sites exhibit strong electronegativity, improving the absorption of potassium ions. Therefore, the diffusion impedance of potassium ions is significantly reduced, leading to an increased diffusion rate of potassium ions. Attributing to the improved reaction kinetics, the Mn0.5Ti2(PO4)3@F-doped carbon composite demonstrates a high specific capacity of 86 mA h g−1 at 10,000 mA g−1 when used as the anode for potassium-ion batteries. Even more, the specific capacity remains a capacity of 136 mA g−1 after 3000 cycles at 1000 mA h g−1. This study enhances our comprehension of material design by investigating the alteration of carbon matrix to promote the electrochemical characteristics of materials.

Enhanced potassium-ion battery performance with Bi Nanoparticle-Infused 3D porous carbon composites

Bismuth (Bi) based materials are widely utilized in potassium-ion batteries (PIBs) due to their high theoretical capacity; however, they undergo severe volume changes during electrochemical processes. To develop Bi-based anode with extended lifespan, Bi nanoparticles and porous carbon materials were composited by a template method in this study. N-doped three-dimensional porous carbon coated Bi nanoparticles (Bi@3DNC) composites were successfully synthesized by using sodium chloride as a template and anchoring Bi nanoparticles on a porous carbon skeleton. Bi@3DNC exhibits excellent electrochemical performance as an anode material for PIBs, retaining a capacity of 273 mAh/g after 700 cycles at 1 A/g. We elucidate that the 3D porous carbon mesh serves to confine the alloying particles and buffer the volume expansion of the metal during continuous K+ de-intercalation, while also enhancing the availability of active sites. This strategy offers promising prospects for the development of advanced metal based anodes for PIBs.

Ultrastable Organic Anode Enabled by Electrochemically Active MXene Binder toward Advanced Potassium Ion Storage.

Conjugated carbonyl compounds are regarded as promising organic anode materials for potassium ion batteries (PIBs) due to their rich redox sites, excellent reversibility, and structural tunability, but their low electrical conductivity and severe solubility in organic electrolytes have substantially restricted their practical application. Herein, 2D MXene is utilized as an electrochemically active binder to fabricate perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) electrodes for high-performance PIBs. MXene, coupled with Super-P particles, served as a binder and conductive matrix to facilitate rapid ion and electron transport, restrain the solubility of PTCDA, promote potassium adsorption, and alleviate the volume expansion of PTCDA during potassiation. Consequently, the PTCDA electrode bonded by the MXene/Super-P system delivers excellent potassium storage performance in terms of a high capacity of 462 mAh g-1 at 50 mA g-1, superior rate capability of 116.3 mAh g-1 at 2000 mA g-1, and stable cycle performance over 3000 cycles with a low capacity decay rate of ∼0.0033% per cycle. When configured with the PTCDA@450 cathode, an all-PTCDA potassium ion full cell delivers a maximum energy density of 179.5 Wh kg-1, indicating the superiority of MXene as an electrochemically active binder to promote the practical application of organic anodes for PIBs.

Two-Dimensional TOD-Graphene in a Honeycomb–Kagome Lattice: A High-Performance Anode Material for Potassium-Ion Batteries

Two-Dimensional TOD-Graphene in a Honeycomb–Kagome Lattice: A High-Performance Anode Material for Potassium-Ion Batteries

Two-dimensional MXene Nanomaterials: Preparation, Structure Modulation and the Applications in Electrochemical Energy Storage.

MXenes have attracted intensive attention owing to their unique twodimensional (2D) layered structure, high specific surface area, excellent conductivity, superior surface hydrophilicity, and chemical stability. In recent years, selective etching of the A element layers from MAX phases by fluorine-containing etchants (HF, LiF-HCl, etc) is a common method to prepare multilayered MXene nanomaterials (NMs) with plentiful surface terminations. At present, many studies have been reported on the use of fluorine-free etchants (NaOH, ZnCl2, etc) to etch MAX phases. The properties of MXene NMs are dependent on their structures. The purpose of this review is to focus on a comprehensive and systematical survey on the preparation, structure modulation, and applications of MXene NMs in electrochemical energy storage devices, including supercapacitors, lithium-ion battery, sodium-ion battery, potassium-ion battery, and aluminum-ion battery. Extensive information related to the preparation and applications of 2D MXene NMs for electrochemical energy storage and their associated patents were collected. This review highlights the recently reported 2D MXene NMs which are used in supercapacitor and various metal ion. It is found that the preparation methods have great impacts on the layer spacing and surface terminations of MXenes, consequently affecting their performance. Hence, this paper summarizes the research progress of the preparation strategies, layer spacing and surface termination modulation of MXene NMs. The applications of 2D MXene NMs in electrochemical energy storage are outlined. The forward-looking challenges and prospects for the development of MXenes are also proposed.

A novel imidazolium-based small molecule matching with unique solvation structure electrolyte for superior K-storage stability

Organic anodes for K-storage have attracted much attention because of high theoretical capacity, low cost and extensive natural resource although facing serious dissolving issues with conventional electrolytes and persistent capacity decay. Therefore, 2-methylimidazole (mIm), an imidazolium-based small molecule restricted with high electronic conductivity carbon nanotubes (mIm/CNTs) is applied for potassium-ion batteries (PIBs). Furthermore, this as-prepared anode is accompanied to the potassium bis(fluorosulfonyl)imide (KFSI)-ethylene carbonate (EC) and diethyl carbonate (DEC) electrolytes (KFSI/EC + DEC) with modifiable solvation structures. At current density of 50 mA g−1, the mIm/CNTs composite coupled with the optimized 3 mol L−1 KFSI/EC + DEC electrolyte provides an average reversible capacity of 240 mAh g−1 (composites) with coulombic efficiency (CE) of 99.5 %. After 500 cycles, a high sustained capacity of 200 mAh g−1 (composites) is attained at 200 mA g−1. This enhanced K-storage performance of mIm/CNTs in 3 mol L−1 KFSI/EC + DEC electrolyte can be attributed to distinctive solvation structure, which is dominated by contact ion pairs (CIPs) and aggregates (AGGs). This structure intensively mitigates dissolution issues and greatly promotes K+ reaction kinetics. This work emphasizes the significance of electrolyte regulation for organic anodes and will supply a comprehensive appreciating of electrochemistry performance for advanced energy storage systems.

Engineering of protective surfaces for retarding selenium leaching by self-growth of rGO@NixSey on carbon nanofibers for potassium ion batteries

K-ion batteries (PIBs) are promising alternatives to Li-ion and Na-ion batteries (LIBs/SIBs). However, the ionic radius of K+ (1.38 Å) is larger than that of Li+ (0.76 Å), consequently leading to sluggish diffusion, low capacity, and poor cycling performance in intercalation- and conversion-type K-storage technologies. To address these issues, rGO-coated nickel selenide on carbon nanofiber (rGO@NixSey-CNF) and nickel selenide on carbon nanofiber (NixSey-CNF) were developed as anode electrodes for PIBs. To improve the electrochemical properties and prevent Se leaching during the charging/discharging of nickel selenide, the surface of the NixSey particles was coated with rGO. The rGO coating not only protected Se but also improved the conductivity and cycling performance. rGO@NixSey-CNF delivered an excellent charge-specific capacity of ∼ 126 mAh g−1 at 100 mA g−1 over 200 cycles, with an initial coulombic efficiency of approximately 50 %, as well as 50 % capacity retention, attributed to the retarded leaching of Se through the rGO coating. These findings provide new insights for developing highly reversible Ni-based anode materials for advanced PIBs.

Construction of a bi-continuous charge transport network towards high-performance vanadium-based phosphate cathode materials for potassium ion batteries

As one class of most promising cathode materials for potassium ion batteries (KIBs), polyanionic compounds still suffer from unsatisfactory effective capacity and rate performance due to their poor intrinsic electronic conductivity. In this paper, nanoscale K3V3(PO4)4 (KVP) particles with a bi-continuous charge transport network (denote as KVP-S) are designed and prepared. Carbon nanotubes (CNTs) play a crucial role in this design, not only effectively inhibiting the aggregation and growth of particles, but also providing a three-dimensional (3D) electron conductive network. Benefiting from the advantages of nanoscale particle size and bi-continuous charge transport network, the KVP-S electrode exhibits a high capacity (118mAh g−1 at 20 mA g−1), outstanding rate performance (102 mAh g−1 at 0.5 C; 66 mAh g−1 at 5 C) and excellent cycling stability (94 % retention after 50 cycles at 1 C). Even at a higher rate of 5 C, it still maintains a high capacity retention of 92 % after 300 cycles. More importantly, the capacity can maintain 80 mAh g−1 at 1 C when the mass loading is extended to 4 mg cm−2, In addition, in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) analyses reveal that the potassium storage mechanism of KVP-S is two single-phase solid solution reactions, involving V2+/V3+/V4+ three-electron redox conversions with a total volume change of 5.5 %. This study provides a new way to rationally design nanoscale particle electrodes with highly conductive charge transport networks.

N, P co-doped 3D porous carbon with self-assembled morphological control via template-free method for potassium-ion battery anodes

N, P co-doped 3D porous carbon with self-assembled morphological control via template-free method for potassium-ion battery anodes

MoS2, WS2, and MoWS2 Flakes as Reversible Host Materials for Sodium-Ion and Potassium-Ion Batteries.

Transition-metal dichalcogenides (TMDs) and their alloys are vital for the development of sustainable and economical energy storage alternatives due to their large interlayer spacing and hosting ability for alkali-metal ions. Although the Li-ion chemically correlates with the Na-ion and K-ion, research on batteries with TMD anodes for K+ is still in its infancy. This research explores TMDs such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) and TMD alloys such as molybdenum tungsten disulfide (MoWS2) for both sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs). The cyclic stability test analysis indicates that in the initial cycle, the MoS2 NIB demonstrates exceptional performance, with a peak charge capacity of 1056 mAh g-1, while retaining high Coulombic efficiency. However, the WS2 KIB underperforms, with the least charge capacity of 130 mAh g-1 in the first cycle and exceptionally low retention at a current density of 100 mA g-1. The MoWS2 TMD alloy exhibits a moderate charge capacity and cyclic efficiency for both NIBs and KIBs. This comparison study shows that decreasing sizes of alkali-metal ions and constituent elements in TMDs or TMD alloys leads to decreased resistance and slower degradation processes as indicated by cyclic voltammetry and electrochemical impedance spectroscopy after 10 cycles. Furthermore, the study of probable electrochemical intercalation and removal processes of Na-ions and K-ions demonstrates that large geometrically shaped TMD flakes are more responsive to intercalation for Na-ions than K-ions. These performance comparisons of different TMD materials for NIBs and KIBs may promote the future development of these batteries.

Tunable Interfacial Electric Field‐Mediated Cobalt‐Doped FeSe/Fe3Se4 Heterostructure for High‐Efficiency Potassium Storage

AbstractThe interfacial electric field (IEF) in the heterostructure can accelerate electron transport and ion migration, thereby enhancing the electrochemical performance of potassium‐ion batteries (PIBs). Nevertheless, the quantification and modulation of the IEF for high‐efficiency PIB anodes currently remains a blank slate. Herein, we achieve for the first time the quantification and tuning of IEF via amorphous carbon‐coated undifferentiated cobalt‐doped FeSe/Fe3Se4 heterostructure (denoted UN‐CoFe4Se5/C) for efficient potassium storage. Co doping can increase the IEF in FeSe/Fe3Se4, thereby improving the electron transport, promoting the potassium adsorption capacity, and lowering the diffusion barrier. As expected, the IEF magnitude in UN‐CoFe4Se5/C is experimentally quantified as 62.84 mV, which is 3.65 times larger than that of amorphous carbon‐coated FeSe/Fe3Se4 heterostructure (Fe4Se5/C). Benefiting from the strong IEF, UN‐CoFe4Se5/C as a PIB anode exhibits superior rate capability (145.8 mAh g−1 at 10.0 A g−1) and long cycle lifespan (capacity retention of 95.1 % over 3000 cycles at 1.0 A g−1). Furthermore, this undifferentiated doping strategy can universally regulate the IEF magnitude in CoSe2/Co9Se8 and FeS2/Fe7S8 heterostructures. This work can provide fundamental insights into the design of advanced PIB electrodes.