Potassium Sulfur Batteries Research Articles

In-situ banana fiber-modified carbonized bacterial cellulose as a free-standing and binder-free cathode host for potassium-sulfur batteries

To meet the growing energy demand for large-scale applications, potassium-sulfur batteries (KSBs) have gained enormous attention owing to their high energy density, natural abundance, and specific capacity. Nevertheless, the shuttle effect, the insulating nature of sulfur, and the large volume change hinder the development of KSBs. To address the different challenges of KSBs, we report eco-friendly and biodegradable in-situ banana fiber-modified carbonized bacterial cellulose as a free-standing and binder-free cathode (sulfur) host. The catholyte K2S6 is used as active sulfur for cell fabrication owing to a high sulfur loading and even distribution of active material. However, introducing the catholyte induces the potassium side reaction by reacting to it. Therefore, carbonized bacterial cellulose is used as an interlayer to reduce the notorious polysulfide shuttle effect. As a result, the fabricated cell delivers a specific capacity of 437, 354, and 193 mAh g-1 at the current density of 0.2, 0.7, and 1.2 C, respectively. During the long cycling, the cell shows excellent electrochemical performance for 200 cycles with a capacity retention of 78 % at 0.7 C. This work paves the way to utilize an eco-friendly and cost-effective approach to fabricate a high-performance KSB.

Empowering the Potassium-Sulfur Battery with Commendable Reaction Kinetics and Capacity Output by Localized High-Concentration Electrolytes.

Potassium-sulfur (K-S) batteries are one of the promising high-energy-density candidates beyond current lithium-ion batteries. Nevertheless, in practice, the utilization of K-S batteries is largely hindered due to the dissolution and shuttle effect of the cathode redox intermediates and the scarcity of an effective anode protection layer in conventional electrolytes. Herein, electrolyte engineering is applied to formulate an ether-based localized high-concentration electrolyte (LHCE) for the first time in a K-S cell with the mitigated parasitic effect of polysulfide dissolution and shuttle and the tuned anode-electrolyte interface property. A nonsolvating and polysulfide-stable fluoroether is sieved as a cosolvent in such an LHCE, which possesses the ultralow polysulfides solubility due to less roaming solvents and thus alleviates the polysulfides shuttle effect. The anion-derived solid electrolyte interphase enriched in inorganic components is constructed due to the strengthened cation-anion interplay in the primary solvation sheath and highlighted with accelerated interfacial kinetics in a K-S cell. It is validated that the proposed LHCE unlocks the theoretical capacity of the K-S cell based on the conversion between S and K2S3. It is further revealed that the lifespan is limited to the anode corrosion with severe cosolvent degradation caused by limited solvating solvent compatibility with metallic K, and the inevitable byproduct accumulation at the S cathode. The K-S cell based on the designed LHCE could achieve a prolonged lifespan with a reversible capacity of 448 mA h/gs after 80 cycles with an elaborate cathode design. This work shines a light on the electrolyte design perspective for full utilization and an in-depth mechanistic understanding of high-energy-density K-S batteries.

Strong d-π Orbital Coupling of Co-C4 Atomic Sites on Graphdiyne Boosts Potassium-Sulfur Battery Electrocatalysis.

Potassium-sulfur (K-S) batteries are severely limited by the sluggish kinetics of the solid-phase conversion of K2S3/K2S2 to K2S, the rate-determining and performance-governing step, which urgently requires a cathode with facilitated sulfur accommodation and improved catalytic efficiency. To this end, we leverage the orbital-coupling approach and herein report a strong d-π coupling catalytic configuration of single-atom Co anchored between two alkynyls of graphdiyne (Co-GDY). The d-π orbital coupling of the Co-C4 moiety fully redistributes electrons two-dimensionally across the GDY, and as a result, drastically accelerates the solid-phase K2S3/K2S2 to K2S conversion and enhances the adsorption of sulfur species. Applied as the cathode, the S/Co-GDY delivered a record-high rate performance of 496.0 mAh g-1 at 5 A g-1 in K-S batteries. In situ and ex situ characterizations coupling density functional theory (DFT) calculations rationalize how the strong d-π orbital coupling of Co-C4 configuration promotes the reversible solid-state transformation kinetics of potassium polysulfide for high-performance K-S batteries.

Optimizing potassium polysulfides for high performance potassium-sulfur batteries.

Potassium-sulfur batteries attract tremendous attention as high-energy and low-cost energy storage system, but achieving high utilization and long-term cycling of sulfur remains challenging. Here we show a strategy of optimizing potassium polysulfides for building high-performance potassium-sulfur batteries. We design the composite of tungsten single atom and tungsten carbide possessing potassium polysulfide migration/conversion bi-functionality by theoretical screening. We create two ligand environments for tungsten in the metal-organic framework, which respectively transmute into tungsten single atom and tungsten carbide nanocrystals during pyrolysis. Tungsten carbide provide catalytic sites for potassium polysulfides conversion, while tungsten single atoms facilitate sulfides migration thereby significantly alleviating the insulating sulfides accumulation and the associated catalytic poisoning. Resultantly, highly efficient potassium-sulfur electrochemistry is achieved under high-rate and long-cycling conditions. The batteries deliver 89.8% sulfur utilization (1504 mAh g-1), superior rate capability (1059 mAh g-1 at 1675 mA g-1) and long lifespan of 200 cycles at 25 °C. These advances enlighten direction for future KSBs development.

Anion-Regulated Sulfur Conversion in High-Content Carbon Layer Confined Sulfur Cathode Maximizes Voltage and Rate Capability of K-S Batteries.

Potassium-sulfur (K-S) batteries have attracted attention in large-scale energy storage systems. Small-molecule/covalent sulfur (SMCS) can help to avoid the shuttle effect of polysulfide ions via solid-solid sulfur conversion. However, the content of SMCS is relatively low (≤40%), and solid-solid reactions cause sluggish kinetics and low discharge potentials. Herein, SMCS is confined in turbo carbon layers with a content of ≈74.1wt% via a C/S co-deposition process. In the K-S battery assembled by using as-fabricated SMCS@C as cathode and KFSI-EC/DEC as an electrolyte, anion-regulated two-plateau solid-state S conversion chemistry and a novel high discharge potential plateau at 2.5-2.0V with a remarkable reversible capacity of 384mAhg-1 at 3Ag-1 after 1000 cycles are found. The SMCS@C||K full cell showed energy and power density of 72.8Whkg-1 and 873.2Wkg-1, respectively, at 3Ag-1. Mechanismstudiesrevealthat theenlarged carbon layer space enables the diffusion of K+-FSI-ion pairs, and the coulombic attraction between them accelerates their diffusion in SMCS@C. In addition, FSI-regulates sulfur conversion in situ inside thecarbon layers along a two-plateau solid-state reaction pathway, which lowers the free energy and weakens the S─S bond of intermediates, leading to faster and more efficient S conversion.

Boosting the "Solid-Liquid-Solid" Conversion Reaction via Bifunctional Carbonate-Based Electrolyte for Ultra-long-life Potassium-Sulfur Batteries.

Potassium-sulfur (K-S) batteries have attracted wide attention owing to their high theoretical energy density and low cost. However, the intractable shuttle effect of K polysulfides results in poor cyclability of K-S batteries, which severely limits their practical application. Herein, a bifunctional concentrated electrolyte (3 mol L-1 potassium bis(trifluoromethanesulfonyl)imide in ethylene carbonate (EC)) with high ionic conductivity and low viscosity is developed to regulate the dissolution behavior of polysulfides and induce uniform K deposition. The organic groups in the cathode electrolyte interphase layer derived from EC can effectively block the polysulfide shuttle and realize a "solid-liquid-solid" reaction mechanism. The KF-riched solid-electrolyte interphase inhibits K dendrite growth during cycling. As a result, the achieved K-S batteries display a high reversible capacity of 654 mAh g-1 at 0.5 A g-1 after 800 cycles and a long lifespan over 2000 cycles at 1 A g-1 .

Boosting the “Solid–Liquid–Solid” Conversion Reaction via Bifunctional Carbonate‐Based Electrolyte for Ultra‐long‐life Potassium–Sulfur Batteries

AbstractPotassium–sulfur (K−S) batteries have attracted wide attention owing to their high theoretical energy density and low cost. However, the intractable shuttle effect of K polysulfides results in poor cyclability of K−S batteries, which severely limits their practical application. Herein, a bifunctional concentrated electrolyte (3 mol L−1 potassium bis(trifluoromethanesulfonyl)imide in ethylene carbonate (EC)) with high ionic conductivity and low viscosity is developed to regulate the dissolution behavior of polysulfides and induce uniform K deposition. The organic groups in the cathode electrolyte interphase layer derived from EC can effectively block the polysulfide shuttle and realize a “solid–liquid–solid” reaction mechanism. The KF‐riched solid‐electrolyte interphase inhibits K dendrite growth during cycling. As a result, the achieved K−S batteries display a high reversible capacity of 654 mAh g−1 at 0.5 A g−1 after 800 cycles and a long lifespan over 2000 cycles at 1 A g−1.

A self-supporting graphitic carbon nanocage network confining high-loading sulfur for high performance potassium-sulfur batteries

Potassium-sulfur (K-S) battery is a promising candidate for high-energy and low-cost energy storage system. However, the development of K-S battery is challenged by the sluggish kinetics, low utilization of sulfur and serious shuttle effect. Herein, a novel self-supporting carbon/sulfur composite cathode (S@GCNs) was developed by infusing sulfur into an interconnected graphitic carbon nanocage (GCNs) network. Typically, the small GCNs (<10 nm) provide a large amount of space for sulfur storage, the sulfur content could reach more than 80 wt%. In addition, the interconnected GCNs network with high conductivity provide fast transport pathways for electrons/ions, and the strong confinement of GCNs on sulfur will buffer the volume expansion of sulfur and alleviate shuttle effect. The unique microstructure of S@GCNs boosts the rate capability and cycle stability of K-S battery, the initial capacity was 452.7 mAh/g, which remained 270.6 mAh/g and 205.9 mAh/g after 10 and 20 cycles, the capacity can reach 97.7 mA h g−1 even at 2000 mA g−1. Characterizations of the phase and structural evolution of S@GCNs revealed the reversible conversion mechanism of sulfur: S0↔ K2Sx (x = 5, 6)↔ K2Sx (x = 4)↔ K2S3.

Carbonized bacterial cellulose as free-standing cathode host and protective interlayer for high-performance potassium-sulfur batteries with enhanced kinetics and stable operation

Due to the limited capacity of Lithium (Li)-ion batteries and the scarce reserves of Li, potassium-sulfur battery (KSB) seems to be the most appealing candidate for next-generation advanced energy storage systems owing to the abundance of sulfur as well as potassium in addition to the high capacity offered by sulfur cathodes. However, the development of KSB is in the nascent stage, primarily because of the highly unstable and reactive potassium anode, which needs special consideration for its protection. To overcome this, for the first time to the best of our knowledge, we introduce the free-standing carbonized bacterial cellulose (CBC) not only as an anode-protective interlayer but also as a cathode host. Further, the K2S6 catholyte is used as an active material, enabling the even distribution of active sulfur and high sulfur loading. Benefitting from the superior physicochemical properties of CBC and the introduction of it as a protective interlayer, the KSB, as developed, can be cycled for continuous 500 cycles even at high current rates such as 2 and 5C, respectively. The cell with CBC as a cathode host and an interlayer retained 73% and 62% of initial capacity after 300 and 500 cycles at 1 and 2C, respectively. Potassium striping and plating test show that the CBC interlayer effectively enables uniform nucleation and growth, reducing dendrite formation. The first-principles calculations are also performed to substantiate these advancements in electrochemical performances. This study may pave the way for the practical realization of KSB with stable operation and long cycle life.

Reducing Overpotential of Solid-State Sulfide Conversion in Potassium-Sulfur Batteries.

Improving kinetics of solid-state sulfide conversion in sulfur cathodes can enhance sulfur utilization and promote Coulombic efficiency of secondary metal-sulfur batteries. However, fundamental mechanisitic understanding of the solid-state conversion in metal-sulfur batteries remains to be achieved. Here, taking potassium-sulfur batteries as a model system, we for the first time report the reducing overpotential of solid-state K2S3 to K2S conversion via the meta-stable S2-3 intermediates on a range of transition metal single-atom catalytic sulfur hosts. The resultant catalytic sulfur host containing Cu single atoms demonstrate high discharge capacities of 1,595 and 1226 mAh g-1 at specific current densitieis of 335 and 1675 mA g-1, respectively, with stable Coulombic efficiency of ~100% during cycling. Combined spectroscopic characterizations and density functional theory computations reveal that the Cu single atom catalyst exhibits a relatively weak Cu-S bonding during sulfur redox conversion, resulting in low overpotential of solid-state K2S3-K2S conversion and high sulfur utilization. The elucidation of reaction mechanism of solid-state sulfide conversion can direct the exploration of highly efficient metal-sulfur batteries.

Achieving Fast and Reversible Sulfur Redox by Proper Interaction of Electrolyte in Potassium Batteries

Potassium–sulfur batteries have potential for low-cost and high-energy density energy storage. However, it is a challenge to find suitable electrolytes affording liquid environment for intermediate sulfur species to convert at high voltages. In this study, a series of ether/potassium salt systems were systematically studied to investigate the electrochemical stability and function of the electrolytes in sulfur electrochemistry by using in situ ultraviolet–visible and Fourier-transform infrared spectroscopies. Interactions of soluble polysulfides with the electrolyte were critical to the electrochemical performance. Under optimized conditions, the bis(trifluoromethanesulfonyl)imide anion demonstrated moderate interaction and reversible solvation/desolvation of polysulfides. Polar carboxyl groups in poly(acrylic acid) were effective for binding polysulfide in electrodes, enabling reversible sulfur conversions at high working voltages and improved initial Coulombic efficiency. This enhanced battery performance was achieved even using a conventional carbon host with a high sulfur loading of ∼69 wt %, i.e., ∼49 wt % in the cathode.

Carbonized Bacterial Cellulose-Derived Binder-Free, Flexible, and Free-Standing Cathode Host for High-Performance Stable Potassium–Sulfur Batteries

In search of improved advanced energy storage systems to meet our fast-growing energy demands for large-scale applications, potassium–sulfur batteries (KSBs) provide an essential alternative due to their high specific capacity apart from the low cost and abundance of potassium and sulfur. However, the insulating nature of sulfur, volume changes, and shuttle effect impede the development of these batteries. Further, the binder, carbon additives, and current collector used in the assembly of cells in a conventional approach decrease the energy density of cells. To overcome these challenges, we propose a binder-free and free-standing carbonized bacterial cellulose (CBC) as a cathode host that not only provides a conducting pathway but also has a porous network that is resilient to volume change. To ensure the uniform loading of sulfur, CBC was dipped into the sulfur/carbon disulfide solution, followed by melt diffusion at 160 °C to prepare a sulfur-infused CBC (S-CBC) cathode. This S-CBC cathode with an interconnected fiber network delivers a significantly high reversible capacity of 1311 mA h g–1 at a current density of 50 mA g–1. While connected for long-term cycling, the potassium sulfur cell delivers an initial reversible capacity of 475 mA h g–1 at 100 mA g–1. Once the cell is stabilized after 80 cycles, it maintains a capacity of 123 mA h g–1 with a capacity retention of 86% after 500 cycles. This enhanced electrochemical performance of flexible and free-standing S-CBC cathode is further analyzed using first-principles calculations. Moreover, the efficacy of the S-CBC cathode is also tested under high sulfur loading (1.6 and 2.4 mg cm–2, respectively) for the practical development of KSBs.

Advances and challenges in tuning the reversibility & cyclability of room temperature sodium–sulfur and potassium–sulfur batteries with catalytic materials

The high theoretical energy density of room temperature sodium-sulfur and potassium-sulfur batteries (Na–S; 1274 Wh/kg, K–S; 914 Wh/kg; based on the mass of sulfur) due to the multi-electron transfer associated with the unique conversion chemistry of S and the natural abundance of Na, K, and S raw materials make them ideal candidates for large-scale energy storage applications beyond Li batteries. However, achieving good reversibility, cyclability, and active material utilization in Na–S and K–S batteries demands alleviation of the complex polysulfide dissolution and the shuttle phenomena during cycling. Rational employment of catalytic materials is beneficial to address these issues by facilitating effective polysulfide transformation and thereby accelerating the sluggish reaction kinetics. This review focuses on the roles and evolution of catalytic materials in polysulfide adsorption, catalytic conversion, and redox mediation in facilitating high-performing Na–S and K–S batteries. Specifically, the advances in tuning the reversibility and cyclability of Na-S and K–S batteries strategically with catalytic material-incorporated S-host cathodes, separators, and interlayers and the interaction of various catalytic materials with the polysulfide species are discussed in the light of advanced characterization techniques. Lastly, the challenges and the plausible strategies for future research are elucidated.

Covalently Confined Sulfur Composite with Carbonized Bacterial Cellulose as an Efficient Cathode Matrix for High-Performance Potassium–Sulfur Batteries

Covalently Confined Sulfur Composite with Carbonized Bacterial Cellulose as an Efficient Cathode Matrix for High-Performance Potassium–Sulfur Batteries

Porosity Engineering towards Nitrogen-Rich Carbon Host Enables Ultrahigh Capacity Sulfur Cathode for Room Temperature Potassium-Sulfur Batteries.

Potassium-sulfur batteries (KSBs) are regarded as a promising large-scale energy storage technology, owing to the high theoretical specific capacity and intrinsically low cost. However, the commercialization of KSBs is hampered by the low sulfur utilization and notorious shuttle effect. Herein, we employ a porosity engineering strategy to design nitrogen-rich carbon foam as an efficient sulfur host. The tremendous micropores magnify the chemical interaction between sulfur species and the polar nitrogen functionalities decorated carbon surface, which significantly improve the sulfur utilization and conversion. Meanwhile, the abundant mesopores provide ample spaces, accommodating the large volume changes of sulfur upon reversible potassation. Resultantly, the constructed sulfur cathode delivers an ultrahigh initial reversible capacity of 1470 mAh g-1 (87.76% of theoretical capacity) and a superior rate capacity of 560 mAh g-1 at 2 C. Reaching the K2S phase in potassiation is the essential reason for obtaining the ultrahigh capacity. Nonetheless, systematic kinetics analyses demonstrate that the K2S involved depotassiation deteriorates the charge kinetics. The density functional theory (DFT) calculation revealed that the nitrogen-rich micropore surface facilitated the sulfur reduction for K2S but created a higher energy barrier for the K2S decomposition, which explained the discrepancy in kinetics modification effect produced by the porosity engineering.

Progress and Prospects of Emerging Potassium–Sulfur Batteries

AbstractThe potassium–sulfur battery (K–S battery) as an innovative battery technology is a promising candidate for large‐scale applications, due to its high energy density and the low cost of both K and S. The development of the K–S technology is, however, inhibited by its low reversible capacity and the safety issues related to the K metal anode. Here, the review starts by discussing the mechanism of the redox reactions for the K–S batteries and emphasizes the challenges for this battery system based on its current research status. Furthermore, the current improvement strategies for the K–S system in terms of the sulfur cathode, electrolyte, separator, and K metal anode are summarized. Finally, future perspectives on the development of the K–S system are proposed.

High‐Energy and Long‐Lifespan Potassium–Sulfur Batteries Enabled by Concentrated Electrolyte

AbstractPotassium–sulfur (K–S) batteries are emerging as low‐cost and high‐capacity energy‐storage technology. However, conventional K–S batteries suffer from two critical issues that have not yet been successfully resolved: the dissolution of potassium polysulfides (KPS) into the liquid electrolyte and the formation of K dendrites on the K metal anode, which lead to inadequate cycling efficiencies with a low reversible capacity. Herein, a high‐capacity and long cycle‐life K–S battery consisting of a highly concentrated electrolyte (HCE) (4.34 mol kg−1 potassium bis(fluorosulfonyl)imide in a 1,2‐Dimethoxyethane) and a sulfurized polyacrylonitrile (SPAN) cathode is presented The application of a HCE efficiently suppresses the dendritic growth of K, as evidenced by operando optical imaging and phase field modeling, owing to the reduced K‐ion depletion on the electrode surface and a uniform Faradaic current density over the K metal anode surface. Additionally, because S is covalently bonded to the C backbone of PAN in the SPAN structure, the SPAN cathode inhibits the dissolution of KPS. These features generate synergy that the proposed K–S battery can provide a practical areal capacity of 2.5 mAh cm−2 and unprecedented lifetimes with high Coulombic efficiencies over 700 cycles.

Binder-Free and High-Loading Cathode Realized by Hierarchical Structure for Potassium-Sulfur Batteries.

Potassium-sulfur batteries have attracted significant research attention owing to the naturally abundant resources of potassium and sulfur, and have promising applications in large-scale energy storage systems. However, the sluggish reaction kinetics of K+ , low reaction activity of sulfur species, shuttling effect of polysulfides, and large volume change impede the development of these batteries. Moreover, the conventional electrode fabrication method with binders and current collectors renders it difficult to improve the areal sulfur loading and energy density. In this study, a binder-free and freestanding sulfur cathode is prepared by phase inversion and sulfurization of polyacrylonitrile. This sulfur cathode, with a hierarchically porous network, enables a high reversible capacity of 1345 mAh g-1 and a stable cycling performance with a capacity decay of 0.15% per cycle. Importantly, areal capacities of 3.1 and 4.2 mAh cm-2 are achieved even at high sulfur loadings of 3 and 7mg cm-2 , owing to the favorable electron/ion transport in the cathode. The facile preparation method and excellent electrochemical properties reported herein can pave the way for developing high-performance K-S batteries.

Catalytic Oxidation of K2S via Atomic Co and Pyridinic N Synergy in Potassium–Sulfur Batteries

Potassium-sulfur batteries hold practical promise for next-generation batteries because of their high theoretical gravimetric energy density and low cost. However, significant impediments are the sluggish K2S oxidation kinetics and a lack of atomic-level understanding of K2S oxidation. Here, for the first time, we report the catalytic oxidation of K2S on a sulfur host with Co single atoms immobilized on nitrogen-doped carbon. On the basis of combined spectroscopic characterizations, electrochemical evaluation, and theoretical computations, we show a synergistic effect of dynamic Co-S and N-K interactions to catalyze K2S oxidation. The resultant potassium-sulfur battery exhibited high capacities of 773 and 535 mAh g-1 under high current densities of 1 and 2 C, respectively. These findings provide atomic-scale insights for the rational design of highly efficient sulfur hosts.

An in-situ catalytic-insoluble strategy enabled by sulfurized polyacrylonitrile-based composite cathode for potassium–sulfur batteries

Owing to the insoluble organosulfur mechanism and stable cycling life, sulfurized polyacrylonitrile (SPAN) developed as a promising cathode material for high-energy potassium–sulfur batteries (KSBs). However, it is yet a major challenge to achieve fast catalytic kinetics and high reversible capacity in SPAN-based cathodes. Here, one-step electrospun SPAN nanofibers embedded with Fe[Formula: see text]Nb[Formula: see text]O metal oxide nanoparticles (FeNb@SPAN) have been successfully developed to construct sulfur electrodes with high electrochemical activity, high sulfur utilization, and high cycling stability. The as-prepared freestanding FeNb@SPAN composite cathode, which featuring interwoven nanofibers with Fe[Formula: see text]Nb[Formula: see text]O nanoparticles homogeneously implanted, possesses high storage space for volume expansion and suppresses polysulfide dissolution during potassiation/depotassiation. Benefiting from its unique structure and composition in electrode design, the FeNb@SPAN cathode is endowed with outstanding energy storage performances with a high initial specific capacity of 776 mAh [Formula: see text] g[Formula: see text] under 50 mA [Formula: see text] g[Formula: see text] and an excellent cycling capability of 201 mAh [Formula: see text] g[Formula: see text] after 80 charge/discharge processes. This work heralds a feasible strategy toward SPAN-based sulfur host materials in the structural design of next-generation high-performance cathode materials for KSBs and other metal–sulfur batteries.