Potassium-ion Batteries Research Articles

Delving into the dissimilarities in electrochemical performance and underlying mechanisms for sodium and potassium ion storage in N-doped carbon-encapsulated metallic Cu2Se nanocubes

The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability, ultimately hindering the achievement of superior electrochemical performance. Herein, metallic Cu2Se encapsulated with N-doped carbon (Cu2Se@NC) was prepared using Cu2O nanocubes as templates through a combination of dopamine polymerization and high-temperature selenization. The unique nanocubic structure and uniform N-doped carbon coating could shorten the ion transport distance, accelerate electron/charge diffusion, and suppress volume variation, ultimately ensuring Cu2Se@NC with excellent electrochemical performance in sodium ion batteries (SIBs) and potassium ion batteries (PIBs). The composite exhibited excellent rate performance (187.7 mA h g−1 at 50 A g−1 in SIBs and 179.4 mA h g−1 at 5 A g−1 in PIBs) and cyclic stability (246.8 mA h g−1 at 10 A g−1 in SIBs over 2500 cycles). The reaction mechanism of intercalation combined with conversion in both SIBs and PIBs was disclosed by in situ X-ray diffraction (XRD) and ex situ transmission electron microscope (TEM). In particular, the final products in PIBs of K2Se and K2Se3 species were determined after discharging, which is different from that in SIBs with the final species of Na2Se. The density functional theory calculation showed that carbon induces strong coupling and charge interactions with Cu2Se, leading to the introduction of built-in electric field on heterojunction to improve electron mobility. Significantly, the theoretical calculations discovered that the underlying cause for the relatively superior rate capability in SIBs to that in PIBs is the agile Na+ diffusion with low energy barrier and moderate adsorption energy. These findings offer theoretical support for in-depth understanding of the performance differences of Cu-based materials in different ion storage systems.

Zirconium-based metal–organic frameworks/porous carbon hybrids as high-performance anode materials for highly stable lithium- and potassium-ion batteries

Metal-organic framework (MOF)-derived carbon materials have been widely investigated as advanced electrode materials. However, post-synthetic modifications suffer from certain limitations in morphology, surface area, and pore size control. Herein, we report a simple strategy to synthesize surface-confined Zirconium(Zr)-based MOF UiO-66-NH2 carbon hybrids (Zr-MOF@C; denoted as Zr-MOF, Zr-MOF@C10, Zr-MOF@C25, and Zr-MOF@C50) through a covalent assembly/amide linkage between the MOFs and hierarchical porous carbon (PC) in various proportions under solvothermal conditions. Zr-MOF@C hybrids have been utilized as the anode materials for lithium- (LIBs) and potassium-ion batteries (KIBs). In LIBs, the Zr-MOF@C10, Zr-MOF@C25 and Zr-MOF@C50 anodes delivered the discharge capacities of 126, 65 and 94 mA h g−1 at 100 mA g−1 after 100 cycles, respectively. In KIBs, the Zr-MOF@C10 and Zr-MOF@C25 exhibited the high discharge capacities of 78 and 70 mA h g−1 at 100 mA g−1 over 100 cycles. In addition, the Zr-MOF@C25 and Zr-MOF@C50 anodes exhibited an outstanding rate capability with a reversible capacity of ∼166 mA h g–1 vs. K/K+ and 176 mA h g–1 for Li/Li+, respectively, while well-maintained long-term cyclic stabilities of ∼57 mA h g–1 (Zr-MOF@C25 vs. K/K+) and ∼140 mA h g–1 (Zr-MOF@C50 vs. Li/Li+) at 1 A g–1 over 1000 cycles. The electrochemical kinetics studies revealed that Li+ and K+ storage efficiencies of all anodes were dominated by a surface-charge capacitive effect and diffusion-driven charge storage mechanism, respectively. These findings provide new insights for designing high-performance surface-confined MOF-based carbon composite materials for next-generation high-energy storage devices.

Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride.

Organic materials have attracted extensive attention for potassium-ion batteries due to their flexible structure designability and environmental friendliness. However, organic materials generally suffer from unavoidable dissolution in aprotic electrolytes, causing an unsatisfactory electrochemical performance. Herein, we designed a weakly solvating electrolyte to boost the potassium storage performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The electrolyte induces an in situ morphology evolution and achieves a nanowire structure. The weakly dissolving capability of ethylene glycol diethyl ether-based electrolyte and unique nanowire structure effectively avoid the dissolution of PTCDA. As a result, PTCDA shows excellent cycling stability (a capacity retention of 89.1% after 2000 cycles) and good rate performance (70.3 mAh g-1 at 50C). In addition, experimental detail discloses that the sulfonyl group plays a key role in inducing morphology evolution during the charge/discharge process. This work opens up new opportunities in electrolyte design for organic electrodes and illuminates further developments of potassium-ion batteries.

Role of Co Content on the Electrode Properties of P3-Type K0.5Mn1-xCoxO2 Potassium Insertion Materials.

Potassium-ion batteries are widely being pursued as potential candidates for stationary (grid) storage, where energy dense K+ insertion cathodes are central to economic and energy efficient operation. To develop robust K-based cathodes, it is key to correlate their underlying electronic states to the final electrochemical performance. Here, we report the synthesis and structure-electrochemical property correlation in P3-type K0.5Mn1-xCoxO2 binary layered oxide cathodes. Spectroscopic analyses revealed a random distribution of Mn and Co in transition metal layers in the oxygen anion framework. In this solid-solution family, Co substitution improved the electronic conductivity and structural stability of P3 phases by minimizing local lattice distortion. Co substitution led to a systematic shift of the Co4+/Co3+ and Mn4+/Mn3+ redox potentials. Galvanostatic cycling showed that the Co substitution reduced the initial capacity while improving the cycling stability. The role of Co on final electrochemical properties of P3-layered oxides has been elucidated as a design tool to develop practical potassium-ion batteries.

Resolving the tradeoff between energy storage capacity and charge transfer kinetics of sulfur-doped carbon anodes for potassium ion batteries by pre-oxidation-anchored sulfurization

Sulfur-heteroatom doping is an effective approach to improve the capacity of carbon anodes for potassium-ion batteries due to the reversible K+-sulfur reaction. However, the random sulfur doping induces unresolved tradeoff between capacity and kinetics, which results from the fundamental difficulty in controllable sulfur incorporation using traditional approaches where breaking robust carbon-containing bonds is necessary. Herein, a pre-oxidation-anchored sulfurization approach is proposed to realize site-controlled and content-adjustable sulfur doping, demonstrating the optimum sulfur content of 9.8 at.% in sulfur-doped hollow carbon sphere (S-HCS). Intentional pre-oxidation introduces easy-to-break C-O/C-O-C bond-included oxygen-containing functional groups serving as anchoring sites for substitution with sulfur atoms. Consequently, S-HCS-9.8 % achieves superior performance for K+ storage (406.1 mA h g–1 at 0.1 A g–1, 112.6 mA h g–1 at 5 A g–1 and 170 mA h g–1 after 2,000 cycles at 2 A g–1). The enhanced electrochemical performances are attributed to the largest interlayer spacing and highest disorder degree resulting from the thiophene-sulfur-dominated configuration at high sulfur content, which realizes high structure reversibility and stable solid-electrolyte-interface layer. This work provides new insights and guiding principles for the development of heteroatom-doped carbon anodes for next-generation high-performance energy storage applications.

Constructing a mesoporous carbon nanobowls embedded with ultrafine CoSe2 Nanocrystals for High-Performance potassium ion battery electrode

In the quest for advanced electrode materials for potassium ion batteries (KIBs), an innovative anode featuring ultrafine CoSe2 nanocrystals embedded within mesoporous carbon nanobowls (CoSe2@MCNBs) is presented herein. Diverging from conventional hollow carbon nanospheres, the distinctive bowl structure is crafted to enhance the structural integrity and volumetric energy density of the electrodes. CoSe2@MCNBs synthesized using an iterative drop and dry method followed by selenization exhibit well-preserved morphology with a shell thickness of 20 nm. The successful integration of ultrafine CoSe2 nanocrystals into MCNBs imparts the nanobowls with the benefits of conventional hollow carbon-based composites, including abundant ion storage sites and high electrical conductivity. Simultaneously, the bowl structure boasts a higher packing density than the conventional hollow mesoporous carbon sphere (HMCS) structure, significantly augmenting the volumetric energy density of the fabricated electrode. Capitalizing on these advantages, the CoSe2@MCNB electrode displays exceptional cycling stability, achieving a reversible capacity of 523 mA h g−1 after 500 cycles at 0.5 A/g and an impressive rate capacity of 247 mA h g−1 at 2.0 A/g. This study demonstrates the strong potential of CoSe2@MCNB as an electrode material for the next generation of KIBs.

Ultrathin carbon nanosheets with carbon composite structure of amorphous carbon and pseudo-graphite domains for high-capacity, stable and fast potassium storage

Although great progress has been made in carbon anodes for potassium-ion batteries, the development of advanced carbon anodes with fast reaction kinetics and high cycle stability is still a great challenge due to the large radius of K+ (0.138 nm). In this work, novel ultrathin carbon nanosheets (UCNs) fabricated by vapor-induced bubbling strategy are reported to address current challenge. The results show that the UCNs are composed of 3D interconnected 30 nm-thick sheet units with well-developed hierarchical micro-/meso-/macro-pores, which can not only increase the contact area between electrode/electrolyte, but also effectively buffer the volume expansion caused by the (de)potassiation. In addition, UCNs have a carbon composite structure of intertwined pseudo-graphite domains and amorphous carbon domains, providing abundant storage active sites and fast transport channels for K+. Specifically, the UCN-1300 delivers a K+ storage capacity of ≈350 mAh g−1 at a current density of 0.05 A g−1. Moreover, it presents excellent cycle stability, maintaining a capacity of 120 mAh g−1 after 5000 cycles at a current density of 5 A g−1, with a capacity retention rate of more than 99%. In prior reports, carbon anodes demonstrating such a high K+ storage capacity and outstanding cycle stability are rarely obtained.

Impact of Milling Conditions on Hard and Soft Carbon Properties and Performance in Potassium-Ion Batteries

Impact of Milling Conditions on Hard and Soft Carbon Properties and Performance in Potassium-Ion Batteries

In situ atomic-scale tracking of unusual interface reaction circulation and phase reversibility in (de)potassiated alloy-typed anode

Alloy-typed anode materials, endowed innately with high theoretical specific capacity, hold great promise as an alternative to intercalation-typed counterparts for alkali-ion batteries. Despite tremendous efforts devoted to addressing drastic volume change and severe pulverization issues of such anodes, the underlying mechanisms involving dynamic phase evolutions and reaction kinetics have not yet been fully comprehended. Herein, taking antimony (Sb) anode as a representative paradigm, its microscopic operating mechanisms down to the atomic scale during live (de)potassiation cycling are systematically unraveled using in situ transmission electron microscopy. Highly reversible phase transformations at single-particle level, that are Sb ↔ KSb2 ↔ KSb ↔ K5Sb4 ↔ K3Sb, were revealed during cycling. Meanwhile, multiple phase interfaces associated with different reaction kinetics coexisted and this phenomenon was properly elucidated in the context of density functional theory calculations. Impressively, previously unexplored unidirectional circulation of reaction interfaces within individual Sb particle is confirmed for both potassiation and depotassiation. Based on the empirical results, the surface diffusion-mediated potassiation-depotassiation pathways at single-particle level are suggested. This work affords new insights into energy storage mechanisms of Sb anode and valuable guidance for targeted optimization of alloy-typed anodes (not limited to Sb) toward advanced potassium-ion batteries.

Unravelling solvation structure and interfacial mechanism of pyrrolidinium-based ionic liquid electrolytes in potassium-ion batteries

Ionic liquid-based electrolytes (ILEs) show great potential in mitigating the dissolution of organic electrode materials as well as manipulating the interfacial electrochemistry for long lifespan of potassium-ion batteries (PIBs). Herein, KFSI/Pyr13FSI ILEs with varying K+ and Pyr13+ ratios were designed to match a novel organic K-storage anode of p-toluic acid/CMK3 (PTA/CMK3). These ILEs exhibited facilely manipulated solvation structures, resulting into excellent compatibility with K-metal as well as promotion of the generation of robust solid-electrolyte interphase (SEI) for stable K-storage. As a result, the optimized PTA/CMK3||KFSI/Pyr13FSI K-storage system delivered a reversible capacity of 190 mAh/g(composites) alongside high coulomb efficiency of 99.7 % at a current density of 200 mA/g for 600 cycles. This work provides a fresh insight on rational design of ILEs-based advanced PIBs with high energy density and safety.

Amorphous nanoscale antimony-vanadium oxide: A high capacity anode material for potassium ion batteries

Antimony (Sb)-based materials, as a kind of potential high capacity and low cost materials, are the focus of attention in the anode materials of potassium ion batteries. However, at present, studies on Sb-based anode materials mainly focus on Sb metal, Sb alloy and Sb chalcogenides, while reports on Sb-based oxides are relatively rare. In addition, the development of Sb-based materials is limited by their large volume variation and poor reaction kinetics for potassium storage. Herein, a novel amorphous Sb2VO5 (A-SbVO) as bimetallic antimony vanadium oxide has been synthesized by solvothermal method. The A-SbVO exhibits high K storage activity and capacity due to its nanoscale and amorphous structure. Moreover, ex-situ transmission electron microscopy and X-ray photoelectron spectroscopy revealed the evolution of the A-SbVO in the potassium storage process as follows: A-SbVO → Sb → K3Sb → Sb → Sb + Sb2VO5. After compounding with reduced graphene oxide (rGO), the as-prepared A-SbVO/rGO shows better K storage stability, with discharge specific capacities of 313.0 and 248. 8 mAh/g at 500 and 1000 mA g−1, respectively. After 300 cycles at 200 mA g−1, the A-SbVO/rGO still has a high discharge specific capacity of 382.1 mAh/g.

Dual‑carbon confined Sb2Se3 nanorods for potassium ion batteries anode with improved capacity and cycling stability

Sb2Se3 is regarded as a promising conversion-alloying type anode material for potassium ion batteries (PIBs) owing to its high theoretical specific capacity. However, the low electric conductivity and large volume change during the charge/discharge process hinder its practical applications. Herein, we proposed a novel ‘dual carbon coating’ strategy to construct carbon confined Sb2Se3 nanorods for high performance PIBs anode. Owing to the enhanced electric conductivity resulted from the inner carbon and the strengthened mechanical stability from the outer graphene layer, the confined Sb2Se3 exhibit outstanding electrochemical potassium ion storage performances with a specific capacity of 482.1 mAh g−1 after 50 cycles at a current density of 0.1 A g−1. Even at a high current density of 1 A g−1 after 500 cycles, it still maintains a specific capacity of 283.7 mAh g−1. These results outperform the pure Sb2Se3 and those traditional ‘single carbon’ coated Sb2Se3 from both specific capacity and cycling stability. This ‘dual carbon coating’ method could also be applied to other conversion or alloying type anode materials of PIBs with high theoretical capacities and large volume variation during the repeated charge/discharge process.

Enhancing reversible Na-ion intercalation by introducing K-ions into layered vanadyl phosphate for sodium-ion battery cathodes

Vanadium-based phosphates are being extensively studied as an important family of sodium-ion battery (SIB) cathodes. Among many compositions, NaVOPO4 is considered because of various polymorphs and the high redox potential of V4+/5+. However, due to relatively poor intrinsic kinetics and electronic conductivity, approaches such as nanostructuring and carbon composites are commonly used to avoid fast performance degradation. Being different from mainstream approaches, this work utilizes the knowledge gained from potassium-ion batteries (PIBs) and applies layered KVOPO4, a PIB cathode material, as a SIB cathode material. The results demonstrate that KVOPO4 experiences an electrochemical K+-Na+ exchange during the initial cycle and a Na-dominated (de)intercalation process in the following cycles. The initial exchange results in a small amount of K+ (∼0.1 K per formula) remaining in the interlayer space and owing to the larger size of K+ than Na+, the residual K+ effectively acts as ‘pillars’ to expand interlayer spacing and facilitates the Na (de)intercalation, leading to enhanced reversible Na storage and diffusion kinetics of KVOPO4 compared to its Na counterpart NaVOPO4. KVOPO4 delivers an initial discharge capacity of 120 mAh g−1 (90% of the theoretical capacity) at 10 mA g−1 and retains 88% capacity after 150 cycles. It also delivers 52 mAh g−1 at 1 A g−1 and 91% capacity retention after 1000 cycles at 100 mA g−1, completely outperforming NaVOPO4.

In Situ Chemical Modulation of Graphitization Degree of Carbon Fibers and Its Potassium Storage Mechanism.

Graphite is considered to be the most auspicious anode candidate for potassium ion batteries. However, the inferior rate performances and cycling stability restrict its practical applications. Few studies have investigated the modulating the graphitization degree of graphitic materials. Herein, a nitrogen-doped carbon-coated carbon fiber composite with tunable graphitization (CNF@NC) through etching growth, in-situ oxidative polymerization, and subsequent carbonization process is reported. The prepared CNF@NC with abundant electrochemical active sites and a rapid K+/electron transfer pathway, can effectively shorten the K+ transfer distance and promote the rapid insertion/removal of K+. Amorphous domains and short-range curved graphite layers can provide ample mitigation spaces for K+ storage, alleviating the volume expansion of the highly graphitized CNF during repeated K+ insertion/de-intercalation. As expected, the CNF@NC-5 electrode presents a high initial coulombic efficiency (ICE) of 69.3%, an unprecedented reversible volumetric capacity of 510.2 mA h cm-3 at 0.1 A g-1 after 100 cycles with the mass-capacity of 294.9 mA h g-1. The K+ storage mechanism and reaction kinetic analysis are studied by combining in-situ analysis and first-principles calculation. It manifests that the K+ storage mechanism in CNF@NC-5 is an adsorption-insertion-insertion mechanism (i.e., the "1+2" model). The solid electrolyte interphase (SEI) film forming is also detected.

Oxygen Reaction of Nonlayered Tetrahedral KFeO2 Positive Electrode for Potassium-Ion Battery Using an FSA-based Ionic Liquid Electrolyte

K-ion batteries (KIBs) that use ionic liquid (IL) electrolytes are promising candidates for post-Li-ion batteries because of the abundance of potassium resources and safety of ILs. We successfully synthesized stoichiometric KFeO2 using a solid-state method and evaluated its charge–discharge performance as a KIB positive electrode material, with an amide-based IL electrolyte at 298 K. Transmission electron microscopy, X-ray photoelectron spectroscopy, synchrotron soft X-ray absorption spectroscopy, and energy-dispersive X-ray spectroscopy data showed that the bulk redox and surface oxidation of oxygen, rather than those of iron, contribute to the reversible and irreversible capacities, respectively. Capacity decay occurred upon repeated cycling, owing to the surface irreversible oxidation of oxygen ions to form O2 and K1−x FeO2−x/2, which blocks the pathways of K+ transfer to KFeO2 particles. This study provides a vital platform for constructing novel KIBs and elucidates the important role of oxygen in KFeO2 positive electrode.

Fluorine-doped K0.39Mn0.77Ni0.23O1.9F0.1 microspheres with highly reversible oxygen redox reaction for potassium-ion battery cathode

Fluorine-doped K0.39Mn0.77Ni0.23O1.9F0.1 microspheres with highly reversible oxygen redox reaction for potassium-ion battery cathode

Layer-Type AxRhO2 (A = Li, Na, K, Rb, Cs) and KxMO2 (M = Co, Rh, Ir) Electrodes: Structure and Electrochemistry

Layered lithium transition-metal oxides have remained at the forefront since the first commercialization of layered LiCoO2 in lithium-ion batteries in 1991. The scientific interest in layered sodium transition-metal oxides as well as potassium transition-metal oxides has been considerably growing for application to sodium- and potassium-ion batteries. We extend our systematic studies on the series of layered oxides to AxRhO2 (A = Li, Na, K, Rb, Cs) and KxMO2 (M = Co, Rh, Ir) electrode system focusing on their crystal structure and electrochemical behaviors in non-aqueous cells as a function of A+ ion. Further studies on P2-type KxRhO2 in comparison to P2-type KxCoO2 show that larger Rh(III/IV) ion than Co(III/IV) is believed to be beneficial for reversibility and kinetic of redox process, accompanied with reversible structural evolution upon oxidation/reduction maintaining the P2 framework.

Flower-like CoSe2/N, P-doped carbon microspheres accommodated on carbon nanosheets for high-performance potassium-ion batteries

Transition metal selenides (TMSs) have emerged as promising electrode materials for potassium-ion batteries (PIBs), whereas the large volume expansion and sluggish reaction kinetics have seriously hindered the cycle life and rate performance. Herein, a hierarchical composite of flower-like CoSe2/N, P-doped carbon microspheres accommodated on carbon nanosheets (CoSe2-NPC@CNS) was rationally fabricated as the anode for PIBs through a one-pot hydrothermal and subsequent selenization method. The intimate hybridization of CoSe2/N, P-doped carbon microspheres can effectively alleviate the volume expansion of CoSe2 during charge-discharge cycles, and the ultrathin carbon nanosheets derived from fluid catalytic cracking (FCC) slurry serves as a highly conductive and buffered substrate. By robustly merging them together, the interconnected hierarchical nanoarchitecture with exposed active sites achieves promoted potassium storage capacity, electrochemical reaction kinetics, and structural stability. As a result, the PIBs with CoSe2-NPC@CNS anode deliver high reversible capacities of 320.8 mAh g−1 after 100 cycles at 0.1 A g−1 and 213.9 mAh g−1 after 850 cycles at 1.0 A g−1, excellent rate capability (188.8 mAh g−1 at 5 A g−1), and enhanced pseudo-capacitive contribution rate of 88.7 %. This work offers valuable insight into the rational design and development of hierarchical anode materials with high performance for PIBs and beyond.

Pore structure and oxygen content design of amorphous carbon toward a durable anode for potassium/sodium‐ion batteries

AbstractBoth sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) are considered as promising candidates in grid‐level energy storage devices. Unfortunately, the larger ionic radii of K+ and Na+ induce poor diffusion kinetics and cycling stability of carbon anode materials. Pore structure regulation is an ideal strategy to promote the diffusion kinetics and cyclic stability of carbon materials by facilitating electrolyte infiltration, increasing the transport channels, and alleviating the volume change. However, traditional pore‐forming agent‐assisted methods considerably increase the difficulty of synthesis and limit practical applications of porous carbon materials. Herein, porous carbon materials (Ca‐PC/Na‐PC/K‐PC) with different pore structures have been prepared with gluconates as the precursors, and the amorphous structure, abundant micropores, and oxygen‐doping active sites endow the Ca‐PC anode with excellent potassium and sodium storage performance. For PIBs, the capacitive contribution ratio of Ca‐PC is 82% at 5.0 mV s−1 due to the introduction of micropores and high oxygen‐doping content, while a high reversible capacity of 121.4 mAh g−1 can be reached at 5 A g−1 after 2000 cycles. For SIBs, stable sodium storage capacity of 101.4 mAh g−1 can be achieved at 2 A g−1 after 8000 cycles with a very low decay rate of 0.65% for per cycle. This work may provide an avenue for the application of porous carbon materials in the energy storage field.

Regulating potassium storage kinetics in mesoporous carbon spheres via delicate inner structural design

Carbon materials have been considered to be potential anodes for potassium-ion batteries (PIBs). Different strategies, including designing micro-/nano-structure and porous morphology, introducing heteroatom doping, and creating carbon-based hybrids, have been employed to improve the potassium ion transport kinetics. Nevertheless, it is still a challenge to achieve satisfactory potassium storage performance due to the uncontrolled reaction kinetics of the large-sized potassium ions. Herein, we successfully synthesized mesoporous carbon spheres (MCSs) with tunable internal morphology and structure by using sacrificed template method. The optimized MCSs with novel half inner-shell structures (HIS-MCSs) show excellent electrochemical performance when used as the anode for PIBs. Specifically, a reversible specific capacity of 241.2 mAh/g is achieved at a current density of 0.1 A/g. Even at 5.0 A/g, a reversible specific capacity of 120 mAh/g can still be reached. Long-term stability tests show that the electrode holds a capacity of 166.5 mAh/g after 1000 cycles at 1.0 A/g. The good cycling stability and rate performance of the HIS-MCSs electrode are attributed to the well-defined inner structural design, in which the contribution from ion diffusion and pseudo-capacitance process are compromised.