Building electrode skins for ultra-stable potassium metal batteries

Synergy Between Weak Solvent and Solid Electrolyte Interphase Enables High-Rate and Temperature-Resilient Potassium Ion Batteries

The rate and wide-temperature performance of graphite-based potassium-ion batteries (PIBs) are limited by slow reaction kinetics at the interphases and the solid electrolyte interphase (SEI) stability. Herein, we strategically designed weak solvating electrolytes (WSEs) to construct an efficient solvated K+ desolvation with K2SO3-rich SEI and achieve fast reaction kinetics at the electrode interface through the synergy between the SEI and the WSE. As a result of the beneficial fast reaction kinetics and stability of the electrode interface, the graphite anode shows high levels of rate performance and cycling stability, with a capacity of 249.6 mAh g-1 at 500 mA g-1 and 96.6% capacity retention after 1600 cycles. Moreover, assembled potassiated graphite (KC8)||Prussian blue nanoparticles (K-PBNPs) cells in our designed electrolyte show high-rate performance (63.1 mAh g-1 at 1500 mA g-1) and over wide operating temperature range (>99% Coulombic efficiency for over 1000 cycles and 200 cycles at -20°C and 80°C, respectively). Impressively, the pouch cell shows long-term stability for 2400 cycles at 500 mAg-1. This work bridges a longstanding gap, elucidating the synergy between the SEI components and WSEs, leading to fast-charging and temperature-resilient PIBs.

Graphitic carbon with increased interlayer spacing derived from low-temperature CO2 rapid conversion for high-performance potassium storage

Graphitic carbon has been emerged as one of the most promising anode materials for potassium-ion batteries (PIBs) due to its moderate theoretical specific capacity, high electrical conductivity, and outstanding chemical stability. However, the structure of graphitic carbon usually experiences irreversible damage during the charge and discharge process, primarily due to the large radius of potassium ion. In contrast to the traditional preparation methods, we develop a low-carbon approach to obtain graphitic carbon with larger lattice spacing via a rapid chemical conversion between CO2 and NaAlH4 at ∼62 °C. We confirm that the CO2/NaAlH4 ratio plays a crucial role in increasing the degree of graphitization and promoting the formation of a flaky morphology of carbon materials. When applied as an anode material for potassium storage, the prepared graphitic carbon exhibits outstanding cycling stability and rate performance. It maintains a reversible capacity of 210 mAh g-1 after 1000 cycles at a current density of 0.1 A g-1, with a capacity retention rate of 95.9 %. This efficient method of preparing graphitic carbon provides valuable inspiration for the development of advanced energy storage materials.

Toward Zero-Excess Alkali Metal Batteries: Bridging Experimental and Computational Insights

This review introduces alkali metal (Li, Na, and K) anode-less and anode-free batteries and conveys a synopsis of the current challenges regarding anode-electrolyte interfaces. The review focuses on a critical analysis of the fundamental understanding of the (eletro)chemical and (electro)physical processes occurring at the anode, including metal nucleation and dendrite growth, the properties of liquid and solid electrolytes, and their roles in the metal stripping/deposition process and the formation of solid-electrolyte interphase, and the properties of separators and their role in inhibiting dendrite growth. Solutions to tackle the challenges for anode-less and anode-free batteries are discussed extensively in the aspects of the modifications of the anode substrate, novel electrolyte solutions and SEI structures, interface design, and novel separators/solid-state electrolytes to enable stable battery performances. To highlight the importance of bridging experimental and computational insights, experimental progress derived from a range of advanced characterization techniques is analyzed in combination with the advancement in multi-scale theory and computational modeling. Finally, outlooks are provided from both experimental and computational points of view for the exciting field of zero-excess alkali metal batteries.

Surface Work Function-Induced High-Entropy Solid Electrolyte Interphase Formation for Highly Stable Potassium Metal Anodes

The failure of the solid electrolyte interphase (SEI) layer is a key issue limiting the practical application of potassium metal batteries. Herein, a novel high-entropy SEI layer rich in inorganic components is designed and constructed via in situ electrochemical conversion of the Sn3O4/Sn2S3 interfacial layer on a porous scaffold. Theoretical studies and experimental techniques reveal that the Sn3O4/Sn2S3 heterostructure, with its low work function and weak Sn─O/S bond, significantly enhances reactivity with the electrolyte, thereby facilitating the in situ formation of the high-entropy SEI layer. The in situ generated high-entropy SEI exhibits low surface roughness, low surface potential, fast potassium ion transport characteristics, and excellent mechanical properties (Young's modulus of 20.08 GPa). Leveraging these advantageous properties of the high-entropy SEI, the resulting potassium metal anode achieves an excellent rate performance up to 10 mA cm-2 in symmetric cells and demonstrates outstanding cycling stability for 2500 h at 0.5 mA cm-2. When paired with a perylene-3,4,9,10-tetracarboxylic dianhydride cathode, the potassium metal full battery retains 81.6% of its capacity over 1650 cycles at 10 C. This work underscores a straightforward and effective approach for the establishment of a stable interphase on metallic potassium anodes.

Covalent Anchoring of Mechanical Polymer for Highly Stable Zinc Metal Batteries

Artificial interfacial protective coatings (IPCs) on Zn anodes provide a viable solution for suppressing dendritic growth by spatially confining and homogenizing the Zn2+ flux. However, repeated Zn deformation during electroplating/stripping cycles can lead to the rupture or exfoliation of IPCs, as well as the formation of detrimental interfacial gaps. Herein, a highly durable IPC is developed on a Zn substrate using a mechanically robust fluorinated polyimide nanofilm (FPI). This unique FPI interphase forms strong covalent bonds with Zn through electronegative fluorine atoms, facilitating Zn plating/stripping while maintaining interfacial adhesion. The superior resilience, modulus, and low creep of the FPI film resist the impact stresses from electroplated Zn, ensuring structural integrity. With this FPI coating, the FPI-Cu||Zn half cells demonstrate high reversibility in Zn2+ electroplating/stripping over 4000 h, maintaining Coulombic efficiency above 99.33%. When coupled with a MnO2 cathode, the MnO2||FPI-Zn full cells exhibit a long lifespan, surpassing 5000 cycles, with a high specific capacity retention of 75.21%. This study highlights the importance of achieving a balance between the customized compatibility and mechanical properties of IPCs to modulate zinc interfacial chemistries.

Synergistic Electrode and Electrolyte Polarities Lead to Outstanding Organic Potassium-based Batteries

Organic materials are promising as battery electrodes due to their flexible design, low cost, and sustainability. Although high electrolyte concentrations are known to suppress organic cathode dissolution, the organic cathode solubility depends on the interplay between the electrode and electrolyte polarities, which remains unexplored. Here, we elucidate the delicate interplay of electrode and electrolyte polarities to achieve stable cycling of organic cathode. Notably, we demonstrate that the solubility of low-polar organic cathodes initially increases and subsequently decreases in electrolytes with increasing polarity. In contrast, high-polar organic cathodes display increasing solubility in electrolytes with increasing polarity. When the polarities of the organic cathodes and the electrolyte are tuned, the batteries show high-capacity retention and Coulombic efficiency. For example, polyaniline||potassiated graphite (KC8) pouch cells deliver 2500 cycles with an average Coulombic efficiency of 99.85 %. These new insights into low- and high-polar organic cathode behavior in electrolytes lay a theoretical foundation for designing new organic battery electrodes and optimizing their electrolyte formulation.

Recent advances in potassium metal batteries: electrodes, interfaces and electrolytes

The exceptional theoretical capacity of potassium metal anodes (687 mA h g-1), along with their low electrochemical potential, makes potassium metal batteries (PMBs) highly attractive for achieving high energy density. This review first provides an overview of potassium metal anodes, including their origin, current development status, and distinctive advantages compared to other metal anodes. Then, it discusses the composition and characteristics of emerging breakthrough PMBs, such as K-S, K-O2, K-CO2 batteries, and anode-free metal batteries. Subsequently, we delve into the pivotal challenges and theoretical research pertaining to PMBs, such as potassium metal nucleation/stripping, dendritic growth in PMBs, and unstable interfaces. Furthermore, we comprehensively examine the latest strategies in electrode design (including alloy, host, and current collector design), interface engineering (such as artificial solid electrolyte interphase layers, barrier layer design, and separator modification), and electrolyte optimization concerning nucleation, cycling stability, coulombic efficiency, and the development of PMBs. Finally, we introduce key characterization techniques, including in situ liquid phase secondary ion mass spectrometry, titration gas chromatography, neutron-based characterization, and computational simulation. This review will propel advancements in electrodes, separators, and electrolytes for innovative PMBs and other similar alkali metal batteries.

A bismuth oxide-modified copper host achieving bubble-free and stable potassium metal batteries

Due to the minimal electrochemical oxidation-reduction potential, the potassium (K) metal anode has emerged as a focal in K-ion batteries. However, the reactivity of the K metal anode leads to significant side reactions, particularly gas evolution. Mitigating gas generation from K metal anodes has been a persistent challenge in the field. In this study, we propose a dual protective layer design through pre-treatment of the K metal anode, employing a Bi2O3 modification layer alongside a stable solid electrolyte interface (SEI) formed during the initial charge-discharge cycle, which significantly suppresses gas evolution. Furthermore, we observe that the Bi2O3 modification layer enhances K nucleation due to its strong potassiophilicity when incorporated into the substrate material. The resultant SEI, consisting of dual inorganic layers of Bi-F and K-F formed through the Bi2O3 modification, effectively mitigates side reactions and gas generation while inhibiting dendrite growth. Utilizing a Cu@BO@K host, we achieve a nucleation overpotential as low as 40 mV, with a stability of 1900 h in a Cu@BO@K‖Cu@BO@K cell and a high average Coulombic efficiency of 99.2% in a Cu@BO@K‖Cu cell at 0.5 mA cm-2/0.5 mA h cm-2. Additionally, Cu@BO@K‖PTCDA also presents a high reversible capacity of 114 mA g-1 at 100 mA g-1 after 200 cycles. We believe that this work presents a viable pathway for mitigating side reactions in K metal anodes.

Interfacial Engineering Constructing TFSI- Ion-Sieve Protective Umbrella Guiding Li-Ion Selective Transport and Solid SEI Growth

A novel strategy is proposed by constructing TFSI- ion-sieve interlayer to guide Li-ion selective transport and solid SEI growth. The uniform MgF2 seeds on the fiber surface reacts rapidly with Li+ in electrolyte to form Mg and LiF dual functional sites for the first charging process. Benefiting from the high affinity of LiF, the TFSI- ions is enriched near the anode forming an ion-sieve interlayer, which acts as a protective umbrella and guides priority penetration of Li+ due to the coordination reaction with Li+ and thus homogenize the Li+ flux. While the Mg sites induce Li nucleation with its strong lithiophilicity and facilitate uniform Li plating on fiber surface. Furthermore, as raw material of LiF, the TFSI- enrichment on anode surface is contribute to increasing LiF content in SEI, achieving the stability enhancement and densification of SEI. Of greater importance, the excess Li+ can spread to the adjacent Mg sites for nucleation by means of ultralow Li+ migration barrier on LiF and Mg. The combination of the ion-sieve homogenization of Li+ flux in electrolyte and the uniformity of Li+ transport in LiF/Mg solid medium achieves the purpose of uniform Li metal plating/stripping.

Balancing Potassiophilicity and Catalytic Activity of Artificial Interface Layer for Dendrite-Free Sodium/Potassium Metal Batteries

Potassium metal batteries (PMBs), with high energy density and low cost, are considered a promising option for grid-scale energy storage systems. However, challenges such as the uneven nucleation of K and instability of the solid electrolyte interphase (SEI) layer result in dendrite growth and poor cyclic performance, limiting practical application. To address them, constructing an artificial interface layer with rich defects can enhance the potassium affinity and promote the uniform nucleation of potassium, yet this can also catalyze electrolyte to decompose, leading to unstable SEI formation and poor cycle stability. Herein, a carbon layer with a locally ordered structure (SC-1600) is constructed as the artificial interface to achieve a balance between K affinity and catalytic activity. This optimized design allows for the uniform nucleation of potassium metal and the formation of a dense SEI layer. SC-1600@K symmetric cell can operate for 2000 h at 0.5 mA cm-2 with a capacity of 0.5 mAh cm-2, and the developed full cell shows a high capacity retention of 78% after 1500 cycles at 1 A g-1. Besides, SC-1600@Na effectively extend the life of sodium metal batteries. This work provides a new insight for the construction of efficient K metal artificial interface layer.

Ultrahigh Pyridinic/Pyrrolic N Enabling N/S Co-Doped Holey Graphene with Accelerated Kinetics for Alkali-Ion Batteries

Carbonaceous materials hold great promise for K-ion batteries due to their low cost, adjustable interlayer spacing, and high electronic conductivity. Nevertheless, the narrow interlayer spacing significantly restricts their potassium storage ability. Herein, hierarchical N, S co-doped exfoliated holey graphene (NSEHG) with ultrahigh pyridinic/pyrrolic N (90.6 at.%) and large interlayer spacing (0.423 nm) is prepared through micro-explosion assisted thermal exfoliation of graphene oxide (GO). The underlying mechanism of the micro-explosive exfoliation of GO is revealed. The NSEHG electrode delivers a remarkable reversible capacity (621 mAh g-1 at 0.05 A g-1), outstanding rate capability (155 mAh g-1 at 10 A g-1), and robust cyclic stability (0.005% decay per cycle after 4400 cycles at 5 A g-1), exceeding most of the previously reported graphene anodes in K-ion batteries. In addition, the NSEHG electrode exhibits encouraging performances as anodes for Li-/Na-ion batteries. Furthermore, the assembled activated carbon||NSEHG potassium-ion hybrid capacitor can deliver an impressive energy density of 141 Wh kg-1 and stable cycling performance with 96.1% capacitance retention after 4000 cycles at 1 A g-1. This work can offer helpful fundamental insights into design and scalable fabrication of high-performance graphene anodes for alkali metal ion batteries.

Ultrahigh Potassium Storage Capacity of Ca2Si Monolayer with Orderly Multilayered Growth Mechanism

As the rising renewable energy demands and lithium scarcity, developing high-capacity anode materials to improve the energy density of potassium-based batteries (PBBs) is increasingly crucial. In this work, a unique orderly multilayered growth (OMLG) mechanism on a 2D-Ca2Si monolayer is theoretically demonstrated for potassium storage by first-principles calculations. The global-energy-minimum Ca2Si monolayer is a semiconductor with isotropic mechanical properties and remarkable electrochemical properties, such as a low potassium ion migration energy barrier of 0.07 eV and a low open circuit voltage ranging from 0.224 to 0.003 V. Most notably, 2D-Ca2Si demonstrates an ultrahigh theoretical specific capacity of 5459 mAh g-1 and a total specific capacity of 610 mAh g-1, reaching up to 89% of the capacity of a potassium metal anode. Remarkably, the OMLG mechanism facilitates stable, dendrite-free deposition of hcp-K metal layers on the 2D-Ca2Si surface, where the ultrahigh and gradually converging lattice match as the layers increase is the key to achieving theoretically near-infinite growth. The study theoretically demonstrates the Ca2Si monolayer a highly promising anode material, and offers a novel potassium storage strategy for designing 2D anode materials with high specific capacity, rapid potassium-ion migration, and good safety.

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.

Plasma Coupled Electrolyte Additive Strategy for Construction of High-Performance Solid Electrolyte Interphase on Li Metal Anodes

High-performance lithium metal anodes are crucial for the development of advanced Li metal batteries. Herein, this work reports a novel plasma coupled electrolyte additive strategy to prepare high-quality composite solid electrolyte interphase (SEI) on Li metal to achieve enhanced performance and stability. With the guidance of calculations, this work selects diethyl dibromomalonate (DB) as an additive to optimize the solvation structure of electrolytes to modify the SEI. Meanwhile, this work groundbreakingly develops DB plasma technology coupled with DB electrolyte additive to construct a combinatorial SEI: inner plasma-induced SEI layer composed of LiBr and Li2CO3 plus additive-reduced SEI containing LiBr/Li2CO3/organic lithium compounds as an outer compatible layer. The optimized hybrid SEI has strong affinity toward Li+ and good mechanical properties, thereby inducing horizontal dispersion and uniform deposition of Li+ and keep structure stable. Accordingly, the symmetrical cells exhibit enhanced cycling stability for 1200 h at an overpotential of 23.8 mV with average coulombic efficiency (99.51%). Additionally, the full cells with LiNi0.8Co0.1Mn0.1O2 cathode deliver a capacity retention of 81.7% after 300 cycles at 0.5 C, and the pouch cell achieves a volumetric specific energy of ≈664 Wh L‒1. This work provides new enlightenment on plasma technology for fabrication of advanced metal anodes for energy storage.

Sustainable Electrolytes: Design Principles and Recent Advances

Today, rechargeable batteries are omnipresent and essential for our existence. In order to improve the electrochemical performance of electric fields, the introduction of electrolytes with fluorine (F)-based inorganic elemental compositions is a direction of exploration. However, most fluorocarbons have a high global warming potential and ozone depletion potential, which do not meet the sustainability requirements of the battery industry. Therefore, developing sustainable electrolytes is a viable option for future battery development. Although researchers have made much progress in electrolyte optimization, little attention has been paid to developing low-toxic and safe electrolytes. This review aims to elucidate the design principles and recent advances in this direction for solvents and salts. It concludes with a summary and outlook on future research directions for the molecular design of green electrolytes for practical high-voltage rechargeable batteries.

Restructuring Electrolyte Solvation by a Partially and Weakly Solvating Cosolvent toward High-Performance Potassium-Ion Batteries

Ether-based electrolytes are among the most important electrolytes for potassium-ion batteries (PIBs) due to their low polarization voltage and notable compatibility with potassium metal. However, their development is hindered by the strong binding between K+ and ether solvents, leading to [K+-solvent] cointercalation on graphite anodes. Herein, we propose a partially and weakly solvating electrolyte (PWSE) wherein the local solvation environment of the conventional 1,2-dimethoxyethane (DME)-based electrolyte is efficiently reconfigured by a partially and weakly solvating diethoxy methane (DEM) cosolvent. For the PWSE in particular, DEM partially participates in the solvation shell and weakens the chelation between K+ and DME, facilitating desolvation and suppressing cointercalation behavior. Notably, the solvation structure of the DME-based electrolyte is transformed into a more cation-anion-cluster-dominated structure, consequently promoting thin and stable solid-electrolyte interphase (SEI) generation. Benefiting from optimized solvation and SEI generation, the PWSE enables a graphite electrode with reversible K+ (de)intercalation (for over 1000 cycles) and K with reversible plating/stripping (the K||Cu cell with an average Coulombic efficiency of 98.72% over 400 cycles) and dendrite-free properties (the K||K cell operates over 1800 h). We demonstrate that rational PWSE design provides an approach to tailoring electrolytes toward stable PIBs.

Large-Scale Integration of the Ion-Reinforced Phytic Acid Layer Stabilizing Magnesium Metal Anode

Rechargeable magnesium batteries (RMBs) have garnered significant attention for their potential in large-scale energy storage applications. However, the commercial development of RMBs has been severely hampered by the rapid failure of large-sized Mg metal anodes, especially under fast and deep cycling conditions. Herein, a concept proof involving a large-scale ion-reinforced phytic acid (PA) layer (100 cm × 7.5 cm) with an excellent water-oxygen tolerance, high Mg2+ conductivity, and favorable electrochemical stability is proposed to enable rapid and uniform plating/stripping of Mg metal anode. Guided by even distributions of Mg2+ flux and electric field, the as-prepared large-sized PA-Al@Mg electrode (5.8 cm × 4.5 cm) exhibits no perforation and uniform Mg plating/stripping after cycling. Consequently, an ultralong lifespan (2400 h at 3 mA cm-2 with 1 mAh cm-2) and high current tolerance (300 h at 9 mA cm-2 with 1 mAh cm-2) of the symmetric cell using the PA-Al@Mg anode could be achieved. Notably, the PA-Al@Mg//Mo6S8 full cell demonstrates exceptional stability, operating for 8000 cycles at 5 C with a capacity retention of 99.8%, surpassing that of bare Mg (3000 cycles, 74.7%). Moreover, a large-sized PA-Al@Mg anode successfully contributes to the stable pouch cell (200 and 750 cycles at 0.1 and 1 C), further confirming its significant potential for practical utilization. This work provides valuable theoretical insights and technological support for the practical implementation of RMBs.

Synergistic Effect of CO2 in Accelerating the Galvanic Corrosion of Lithium/Sodium Anodes in Alkali Metal-Carbon Dioxide Batteries

Rechargeable alkali metal-CO2 batteries, which combine high theoretical energy density and environmentally friendly CO2 fixation ability, have attracted worldwide attention. Unfortunately, their electrochemical performances are usually inferior for practical applications. Aiming to reveal the underlying causes, a combinatorial usage of advanced nondestructive and postmortem characterization tools is used to intensively study the failure mechanisms of Li/Na-CO2 batteries. It is found that a porous interphase layer is formed between the separator and the Li/Na anode during the overvoltage rising and battery performance decaying process. A series of control experiments are designed to identify the underlying mechanisms dictating the observed morphological evolution of Li/Na anodes, and it is found that the CO2 synergist facilitates Li/Na chemical corrosion, the process of which is further promoted by the unwanted galvanic corrosion and the electrochemical cycling conditions. A detailed compositional analysis reveals that the as-formed interphase layers under different conditions are similar in species, with the main differences being their inconsistent quantity. Theoretical calculation results not only suggest an inherent intermolecular affinity between the CO2 and the electrolyte solvent but also provide the most thermodynamically favored CO2 reaction pathways. Based on these results, important implications for the further development of rechargeable alkali metal-CO2 batteries are discussed. The current discoveries not only fundamentally enrich our knowledge of the failure mechanisms of rechargeable alkali metal-CO2 batteries but also provide mechanistic directions for protecting metal anodes to build high-reversible alkali metal-CO2 batteries.

Bio-inspired carbon electrodes for metal-ion batteries

Carbon has been widely used as an electrode material in commercial metal-ion batteries (MIBs) because of its desirable electrical, mechanical, and physical properties. Still, traditional carbon electrodes suffer from limited mechanical stability and electrochemical performance in MIBs. Drawing inspiration from biological species, the carbon allotropes, such as fullerenes, carbon nanotubes, and graphene, can be engineered into mechanically robust, highly conductive frameworks with enhanced ion storage and transport capabilities for MIBs. Here, we present an assortment of bio-inspired carbon electrodes that have enhanced the cycling stability, capacity retention, and overall performance of MIBs. In addition, mimicking the structure and functionality of biological systems has led to the development of flexible MIBs whose performance does not degrade even when stretched, bent, or twisted. Finite element analysis (FEA) is a useful guide in identifying such bio-inspired carbon frameworks because it can simulate and analyze potential failure scenarios, such as stress build-up or structural collapse in MIBs. This review highlights through several examples that there is much scope for improving carbon-based electrode materials through bio-inspired designs for practical high-performance MIBs.

Dendrite-Free and High-Rate Potassium Metal Batteries Sustained by an Inorganic-Rich SEI

Potassium metal battery is an appealing candidate for future energy storage. However, its application is plagued by the notorious dendrite proliferation at the anode side, which entails the formation of vulnerable solid electrolyte interphase (SEI) and non-uniform potassium deposition on the current collector. Here, this work reports a dual-modification design of aluminum current collector to render dendrite-free potassium anodes with favorable reversibility. This work achieves to modulate the electronic structure of the designed current collector and accordingly attain an SEI architecture with robust inorganic-rich constituents, which is evidenced by detailed cryo-EM inspection and X-ray depth profiling. The thus-produced SEI manages to expedite ionic conductivity and guide homogeneous potassium deposition. Compared to the potassium metal cells assembled using typical aluminum current collector, cells based on the designed current collector realize improved rate capability (maintaining 400 h under 50 mA cm-2 ) and low-temperature durability (stable operation at -50 °C). Moreover, scalable production of the current collector allows for the sustainable construction of high-safety potassium metal batteries, with the potential for reducing the manufacturing cost.

Hydroxyl-Decorated Carbon Cloth with High Potassium Affinity Enables Stable Potassium Metal Anodes

Highly anticipated potassium metal batteries possess abundant potassium reserves and high theoretical capacity but currently suffer from poor cycling stability as a result of dendritic growth and volume expansion. Here, carbon cloths modified with different functional groups treated with ethylene glycol, ethanolamine, and ethylenediamine are designed as 3D hosts, exhibiting different wettability to molten potassium. Among them, the hydroxyl-decorated carbon cloth with a high affinity for potassium can achieve molten potassium perfusion (K@EG-CC) within 3 s. By efficiently inducing the uniform deposition of metal potassium, buffing its volume expansion, and lowering local current density, the developed K@EG-CC anode alleviates the dendrite growth issue. The K@EG-CC||K@EG-CC symmetric battery can be cycled stably for 2100 h and has only a small voltage hysteresis of ≈93 mV at 0.5 mA cm-2 . Moreover, the high-voltage plateau, high energy density, and long cycle life of K metal full batteries can be realized with a low-cost KFeSO4 F@carbon nanotube cathode. This study provides a simple strategy to promote the commercial applications of potassium metal batteries.

Molecular modulation strategies for two-dimensional transition metal dichalcogenide-based high-performance electrodes for metal-ion batteries

In the past few decades, great efforts have been made to develop advanced transition metal dichalcogenide (TMD) materials as metal-ion battery electrodes. However, due to existing conversion reactions, they still suffer from structural aggregation and restacking, unsatisfactory cycling reversibility, and limited ion storage dynamics during electrochemical cycling. To address these issues, extensive research has focused on molecular modulation strategies to optimize the physical and chemical properties of TMDs, including phase engineering, defect engineering, interlayer spacing expansion, heteroatom doping, alloy engineering, and bond modulation. A timely summary of these strategies can help deepen the understanding of their basic mechanisms and serve as a reference for future research. This review provides a comprehensive summary of recent advances in molecular modulation strategies for TMDs. A series of challenges and opportunities in the research field are also outlined. The basic mechanisms of different modulation strategies and their specific influences on the electrochemical performance of TMDs are highlighted.

MXene-Derived Na+ -Pillared Vanadate Cathodes for Dendrite-Free Potassium Metal Batteries

Cation-intercalated vanadates, which have considerable promise as the cathode for high-performance potassium metal batteries (PMBs), suffer from structural collapse upon K+ insertion and desertion. Exotic cations in the vanadate cathode may ease the collapse, yet their effect on the intrinsic cation remains speculative. Herein, a stable and dendrite-free PMB, composed of a Na+ and K+ co-intercalated vanadate (NKVO) cathode and a liquid NaK alloy anode, is presented. A series of NKVO with tuneable Na/K ratios are facilely prepared using MXene precursors, in which Na+ is testified to be immobilized upon cycling, functioning as a structural pillar. Due to stronger ionic bonding and lower Fermi level of Na+ compared to K+ , moderate Na+ intercalation could reduce K+ binding to the solvation sheath and favor K+ diffusion kinetics. As a result, the MXene-derived Na+ -pillared NKVO exhibits markedly improved specific capacities, rate performance, and cycle stability than the Na+ -free counterpart. Moreover, thermally-treated carbon paper, which imitates the microscopic structure of Chinese Xuan paper, allows high surface tension liquid NaK alloy to adhere readily, enabling dendrite-free metal anodes. By clarifying the role of foreign intercalating cations, this study may lead to a more rational design of stable and high-performance electrode materials.

Intercalation pseudocapacitance mechanism realizes high-performance cathode for aqueous potassium ion batteries

Aqueous potassium-ion batteries have garnered significant interest due to their eco-friendly characteristics and affordability. However, The suboptimal lifetime and restricted energy density of electrode materials present considerable obstacles to the advancement of aqueous potassium ion batteries. In this paper, we report a Ce doped MnO2 material (Ce-MnO2). Ce-MnO2 with large lattice spacing and abundant oxygen defects successfully triggered the intercalation pseudocapacitance behavior in aqueous potassium ion batteries. The intercalation pseudocapacitance mechanism gives MnO2 good capacity and enhanced stability. The Ce-MnO2 demonstrates a high discharge capacity of 120 mAh g-1 at 1 A g-1 with a low concentration electrolyte. It also has a capacity retention rate of 82.5% at 2000 cycles at 5 A g-1. The application of the intercalation pseudocapacitance mechanism offers a new approach to addressing the challenges associated with aqueous potassium-ion batteries.

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

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

Multi-Channel Engineering of 3D Printed Zincophilic Anodes for Ultrahigh-Capacity and Dendrite-Free Quasi-Solid-State Zinc-Ion Microbatteries

Zinc-ion microbatteries (ZIMBs) are regarded as one of most promising miniaturized energy storage candidates owing to their high safety, compatible device size, superior energy density, and cost efficiency. Nevertheless, the zinc dendrite growth during charging/discharging and the inflexible device manufacturing approach seriously restrict practical applications of ZIMBs. Herein, we report a unique material extrusion 3D printing approach with reinforced zincophilic anodes for ultrahigh-capacity and dendrite-free quasi-solid-state ZIMBs. A 3D printed N-doped hollow carbon nanotube (3DP-NHC) multichannel host is rationally designed for desirable dendrite-free zinc anodes. Favorable structural metrics of 3DP-NHC hosts with abundant porous channels and high zincophilic active sites enhance the ion diffusion rate and facilitate uniform zinc deposition behavior. Rapid zinc-ion migration is predicted through molecular dynamics, and zinc dendrite growth is significantly suppressed with homogeneous zinc-ion deposition, as observed by in situ optical microscopy. 3D printed symmetric zinc cells exhibit an ultralow polarization potential, a glorious rate performance, and a stable charging/discharging process. Accordingly, 3D printed quasi-solid-state ZIMBs achieve an outstanding device capacity of 11.9 mA h cm-2 at 0.3 mA cm-2 and superior cycling stability. These results reveal a feasible approach to effectively restrain zinc dendrite growth and achieve high performance for state-of-the-art miniaturized energy storage devices.

Entropy-Tuned Layered Oxide Cathodes for Potassium-Ion Batteries

The manganese-based layered oxides as a promising cathode material for potassium ion batteries (PIBs) have attracted considerable interest owing to their simple synthesis, high specific capacity, and low cost. However, due to the irreversible phase transition and the Jahn-Teller distortion of the Mn3+ , its application in potassium ion batteries is limited, leading to slow potassium ion kinetics and severe capacity attenuation. Here, entropy-tuning by changing the content of cathode material composition is proposed to address the above challenges. Compared to low and high entropy variants of K0.45 Mnx Co(1- x )/4 Mg(1- x )/4 Cu(1- x )/4 Ti(1- x )/4 O2 , where x = 0.8, 0.6, and 0.4, the medium entropy K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 shows more balanced electrochemical properties in the PIBs. Benefiting from entropy-tuned suppression of the Jahn-Teller distortion of the Mn3+ , the K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 can achieve a high K+ ion transport rate and alleviated volume variation while retaining high specific capacity. Accordingly, the medium entropy K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 cathode in the full cell exhibits a high capacity of 100 mAh g-1 at 50 mA g-1 , delivers superior rate capability (65.8 mAh g-1 at 500 mA g-1 ) and cycling stability (67.8 mAh g-1 after 350 cycles at 100 mA g-1 ). The entropy-tuning strategy is expected to open new avenues in designing PIB cathode materials and beyond.

Li, Na, K, Mg, Zn, Al, and Ca Anode Interface Chemistries Developed by Solid-State Electrolytes

Solid-state batteries (SSBs) have received significant attention due to their high energy density, reversible cycle life, and safe operations relative to commercial Li-ion batteries using flammable liquid electrolytes. This review presents the fundamentals, structures, thermodynamics, chemistries, and electrochemical kinetics of desirable solid electrolyte interphase (SEI) required to meet the practical requirements of reversible anodes. Theoretical and experimental insights for metal nucleation, deposition, and stripping for the reversible cycling of metal anodes are provided. Ion transport mechanisms and state-of-the-art solid-state electrolytes (SEs) are discussed for realizing high-performance cells. The interface challenges and strategies are also concerned with the integration of SEs, anodes, and cathodes for large-scale SSBs in terms of physical/chemical contacts, space-charge layer, interdiffusion, lattice-mismatch, dendritic growth, chemical reactivity of SEI, current collectors, and thermal instability. The recent innovations for anode interface chemistries developed by SEs are highlighted with monovalent (lithium (Li+ ), sodium (Na+ ), potassium (K+ )) and multivalent (magnesium (Mg2+ ), zinc (Zn2+ ), aluminum (Al3+ ), calcium (Ca2+ )) cation carriers (i.e., lithium-metal, lithium-sulfur, sodium-metal, potassium-ion, magnesium-ion, zinc-metal, aluminum-ion, and calcium-ion batteries) compared to those of liquid counterparts.

Beaded CoSe2-C Nanofibers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as highly promising energy storage devices due to their high theoretical specific capacity and high energy density. Nevertheless, the commercial application of Li-S batteries is still restricted by poor electrochemical performance. Herein, beaded nanofibers (BNFs) consisting of carbon and CoSe2 nanoparticles (CoSe2/C BNFs) were prepared by electrospinning combined with carbonization and selenization. Benefitting from the synergistic effect of physical adsorption and chemical catalysis, the CoSe2/C BNFs can effectively inhibit the shuttle effect of lithium polysulfides and improve the rate performance and cycle stability of Li-S batteries. The three-dimensional conductive network provides a fast electron and ion transport pathway as well as sufficient space for alleviating the volume change. CoSe2 can not only effectively adsorb the lithium polysulfides but also accelerate their conversion reaction. The CoSe2/C BNFs-S cathode has a high reversible discharge specific capacity of 919.2 mAh g-1 at 0.1 C and presents excellent cycle stability with a low-capacity decay rate of 0.05% per cycle for 600 cycles at 1 C. The combination of the beaded carbon nanofibers and polar metal selenides sheds light on designing high-performance sulfur-based cathodes.

Fatigue-Free and Skin-like Supramolecular Ion-Conductive Elastomeric Interphases for Stable Lithium Metal Batteries

The heterogeneity and continuous cracking of the static solid electrolyte interphase (SEI) are one of the most critical barriers that largely limit the cycle life of lithium (Li) metal batteries. Herein, we report a fatigue-free dynamic supramolecular ion-conductive elastomeric interphase (DSIEI) for a highly efficient and dendrite-free lithium metal anode. The soft phase poly(propylene glycol) backbone with loosely Li+-O coordinating interaction was responsible for fast ion transport. Simultaneously, the supramolecular quadruple hydrogen bonds (H-bonds) in the hard phases endow the elastomeric interphase with mechanical enhancement, while gradient H-bonds can dissipate strain energy via the sequential bonding cleavage. Such a design affords superior mechanical robustness, high ionic conductivity, gradient energy dissipation, and high Li+ transference number. Besides, anion enrichment in DSIEI assists in situ construction of a lithium fluoride-rich inner layer upon cycling. The resultant biomimetic bilayer structure enables the symmetric cells with superior cyclability of over 600 h at a high current density of 10 mA cm-2. Moreover, the DSIEI allows stable operation of the full cells under constrained conditions of limited lithium excess, a high-loading LiNi0.8Co0.1Mn0.1O2 cathode, and a low negative/positive capacity (N/P) ratio. This work presents a powerful strategy for deigning artificial SEI and achieving high-energy-density Li metal batteries.

Trimming the Degrees of Freedom via a K+ Flux Rectifier for Safe and Long-Life Potassium-Ion Batteries

High degrees of freedom (DOF) for K+ movement in the electrolytes is desirable, because the resulting high ionic conductivity helps improve potassium-ion batteries, yet requiring support from highly free and flammable organic solvent molecules, seriously affecting battery safety. Here, we develop a K+ flux rectifier to trim K ion's DOF to 1 and improve electrochemical properties. Although the ionic conductivity is compromised in the K+ flux rectifier, the overall electrochemical performance of PIBs was improved. An oxidation stability improvement from 4.0 to 5.9 V was realized, and the formation of dendrites and the dissolution of organic cathodes were inhibited. Consequently, the K||K cells continuously cycled over 3,700 h; K||Cu cells operated stably over 800 cycles with the Coulombic efficiency exceeding 99%; and K||graphite cells exhibited high-capacity retention over 74.7% after 1,500 cycles. Moreover, the 3,4,9,10-perylenetetracarboxylic diimide organic cathodes operated for more than 2,100 cycles and reached year-scale-cycling time. We fabricated a 2.18 Ah pouch cell with no significant capacity fading observed after 100 cycles.