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

Unraveling Electrode Surface Chemistry in Determining Interphase Stability and Deposition Homogeneity for Anode-Free Potassium Metal Batteries

Potassium metal batteries with an anode-less/-free configuration could realize competitive energy density, which requires exceptional potassium plating/stripping reversibility via guiding smooth potassium growth and building mechanically stable solid electrolyte interphase (SEI). Electrolyte engineering has been the most widely adopted strategy, but there is less understanding of the electrode effect. We demonstrate that the extent of electrolyte decomposition could also be regulated through electrode surface modification. Elevating the work function of an Al current collector by coating a thin layer of Ni-decorated carbon nanofiber could greatly suppress the copious solvent reduction, leading to the formation of inorganic-rich SEIs. Such SEIs possess a large elastic deformation energy to accommodate the volume change and a high ionic conductivity to boost the reaction kinetics. Moreover, the potassiophilic nickel species offer abundant active sites to induce homogeneous potassium deposition. Benefiting from the synergy of stable interphases and promoted nucleation, the modified Al enables a 4.4 V anode-free cell in a normal-concentration electrolyte without anode precycling.

An Adhesive Adaptation Layer Mitigates the Interfacial Instabilities of Rigid Polymer Electrolyte

Solid polymer electrolytes (SPEs) are widely recognized as promising candidates for enabling solid-state lithium metal batteries (SSLMBs) with improved safety, high energy density, and extended cycling life. The traditional perspective posits that increasing the mechanical modulus of SPEs enhances their capacity to regulate Li0 deposition and suppress dendrite penetration. However, this study reveals a distinct failure mechanism: a rigid SPE with a high storage modulus suffers from delamination-induced cell failure due to its inability to accommodate the volumetric changes of the Li0 anode. To address these limitations, we developed a hierarchical SPE incorporating an adhesive adaptation layer (AAL) positioned between the Li0 anode and the rigid SPE. The AAL combines strong adhesive strength, effectively mitigating delamination, with flowability, allowing it to eliminate interfacial voids and defects. Structural characterization via Cryo-TEM and SEM demonstrates that this hierarchical design facilitates uniform, dense, and whisker-free Li0 deposition, in sharp contrast to the uneven and porous morphology observed with the rigid SPE alone. Furthermore, the enhanced interfacial stability promotes the formation of an inorganic-enriched SEI layer, contributing to long-term cycling stability. As a result, the H-SPE exhibits superior electrochemical performance, achieving 87 % capacity over 960 cycles when paired with high-loading (1.6 mAh/cm2) NMC622 cathode.

A Compact-Solvation Electrolyte Under Low Concentration for High-Energy Density and Stable Potassium-Ion Batteries

The development of potassium-ion batteries (PIBs) faces significant challenges due to the lack of suitable electrolytes to achieve satisfactory energy density and long-term stability. This work reports an innovative compact-solvation electrolyte (CSE) strategy leveraging ionic liquid-induced manipulation of solvation structures under low concentration for high-performance PIBs. The CSE, formulated with a low-salt concentration of 0.8 M, simultaneously exhibits compact solvation structures with abundant F-rich anions, high-ionic conductivity, and low-desolvation energy. These features lead to enhanced K-storage thermodynamics and kinetics through the formation of a robust KF-rich solid electrolyte interphase (SEI) as well as accelerated K+ transport kinetics. Consequently, the graphite electrode in CSE delivers a high-reversible capacity of 252 mAh g-1 with an average Coulombic efficiency of 99.5% after 300 cycles at 50 mA g. Furthermore, the designed CSE enables the Prussian blue||graphite full cell to operate for over 1450 cycles at 50 mA g-1, maintaining an impressive capacity retention of 88%. This work represents a significant advance in the development of safe and compatible electrolytes for advanced PIBs.

Binary Electrolyte Additive-Reinforced Interfacial Molecule Adsorption Layer for Ultra-Stable Zinc Metal Anodes

Aqueous zinc ion batteries (AZIBs) face challenges due to the limited interface stability of Zn anode, which includes uncontrolled hydrogen evolution reaction (HER) and excessive dendrite growth. In this study, a natural binary additive composed of saponin and anisaldehyde is introduced to create a stable interfacial adsorption layer for Zn protection via reshaping the electric double layer (EDL) structure. Saponin with rich hydroxyl and carboxyl groups serves as "anchor points", promoting the adsorption of anisaldehyde through intermolecular hydrogen bonding. Meanwhile, anisaldehyde, with a unique aldehyde group, enhances HER suppression by preferentially facilitating electrocatalytic coupling with H* in the EDL, leading to the formation of a robust inorganic solid electrolyte interphase that prevents dendrite formation, and structural evolution of anisaldehyde during Zn deposition process is verified. As a result, the Zn||Zn symmetric cells present an ultra-long cycling lifespan of 3 400 h at 1 mA cm-2 and 1 700 h at 10 mA cm-2. Even at the current density of 20 mA cm-2, the cells demonstrate reversible operations for 450 h. Furthermore, Zn-ion hybrid capacitors exhibit a remarkable lifespan of 100 000 cycles. This work presents a simple synergetic strategy to enhance anode/electrolyte interfacial stability, highlighting its potential for Zn anode protection in high-performance AZIBs.

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.

Advancements in Chemical Vapor Deposited Carbon Films for Secondary Battery Applications

Carbon films, synthesized via chemical vapor deposition (CVD), have gained significant attention in secondary battery applications, where stability and capacity are required to be improved for next-generation electronic devices and electric vehicles. Beyond the inherent properties of carbon films, such as high electrical conductivity, mechanical strength, chemical stability, and flexibility, the CVD method provides a high degree of freedom in designing the carbon films in battery applications, enabling conformal coating with structure engineering for modification of its electrical and mechanical properties. In this review, the CVD-grown carbon films are highlighted in the secondary battery applications, enabling them to overcome critical issues, such as volume expansion, sluggish kinetics, and unstable interfaces. To deeply understand the CVD-grown carbon films, such as graphene and amorphous carbon, a comprehensive overview of the CVD process is also provided, focusing on growth mechanisms, control of 3D morphology, and doping techniques. In addition, a broad range of applications are introduced for carbon films in battery components, including their use in cathodes, anodes, and current collectors, as well as their potential in advanced battery systems, such as lithium-sulfur and all-solid-state batteries. This review proposes future directions for optimizing carbon films to achieve practical applications in next-generation energy storage devices.

Optimized K+ Deposition Dynamics via Potassiphilic Porous Interconnected Mediators Coordinated by Single-Atom Iron for Dendrite-Free Potassium Metal Batteries

Potassium metal batteries are emerging as a promising high-energy density storage solution, valued for their cost-effectiveness and low electrochemical potential. However, understanding the role of potassiphilic sites in nucleation and growth remains challenging. This study introduces a single-atom iron, coordinated by nitrogen atoms in a 3D hierarchical porous carbon fiber (Fe─N-PCF), which enhances ion and electron transport, improves nucleation and diffusion kinetics, and reduces energy barriers for potassium deposition. Molten potassium infusion experiments confirm the Fe─N-PCF's strong potassiphilic properties, accelerating adsorption kinetics and improving potassium deposition performance. According to the Scharifker-Hills model, traditional carbon fiber substrates without potassiphilic sites cause 3D instantaneous nucleation, leading to dendritic growth. In contrast, the integration of single-atom and hierarchical porosity promotes uniform 3D progressive nucleation, leading to dense metal deposition, as confirmed by dimensionless i2/imax 2 versus t/tmax plots and real-time in situ optical microscopy. Consequently, in situ X-ray diffraction demonstrated stable potassium cycling for over 1900 h, while the Fe─N-PCF@K||PTCDA full cell retained 69.7% of its capacity after 2000 cycles (72 mAh g-1), with a low voltage hysteresis of 0.876 V, confirming its strong potential for high energy density and extended cycle life, paving the way for future advancements in energy storage technology.

A Thermally Robust Biopolymeric Separator Conveys K+ Transport and Interfacial Chemistry for Longevous Potassium Metal Batteries

Potassium metal batteries (KMBs) hold promise for stationary energy storage with certain cost and resource merits. Nevertheless, their practicability is greatly handicapped by dendrite-related anodes, and the target design of specialized separators to boost anode safety is in its nascent stage. Here, we develop a thermally robust biopolymeric separator customized via a solvent-exchange and amino-siloxane decoration strategy to render durable and safe KMBs. Through experimental investigation and theoretical computation, we reveal that the optimized porosity and surface functionalization could manage ion transport and interfacial chemistry, thereby enabling efficient K+ diffusion and a favorable solid electrolyte interphase to achieve prolonged cycling stability (over 3000 h). The thus-assembled full cell retains 80% of its initial capacity after 400 cycles at 0.5 A g-1. The heat-proof property of the designed separator is further demonstrated. Our biopolymeric separator, affording multifunctional features, provides an appealing solution to circumvent instability and safety issues associated with potassium metal batteries.

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.

Alumina - Stabilized SEI and CEI in Potassium Metal Batteries

Aluminum oxide (Al2O3) nanopowder is spin-coated onto both sides of commercial polypropene separator to create artificial solid-electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm2-0.5 mAh/cm2 and 3.0 mA/cm2-0.5 mAh/cm2. Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo-stage focused ion beam (cryo-FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina-modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal - SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.

Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly-Efficient Rechargeable Batteries

Alkali metals (e.g. Li, Na, and K) and multivalent metals (e.g. Zn, Mg, Ca, and Al) have become star anodes for developing high-energy-density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid-state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.

Conformal 3D Li/Li13Sn5 Scaffolds Anodes for High-Areal Energy Density Flexible Lithium Metal Batteries

Achieving a high depth of discharge (DOD) in lithium metal anodes (LMAs) is crucial for developing high areal energy density batteries suitable for wearable electronics. Yet, the persistent growth of dendrites compromises battery performance, and the significant lithium consumption during pre-lithiation obstructs their broad application. Herein, A flexible 3D Li13Sn5 scaffold is designed by allowing molten lithium to infiltrate carbon cloth adorned with SnO2 nanocrystals. This design markedly curbs the troublesome dendrite growth, thanks to the uniform electric field distribution and swift Li+ diffusion dynamics. Additionally, with a minimal SnO2 nanocrystals loading (2 wt.%), only 0.6 wt.% of lithium is consumed during pre-lithiation. Insights from in situ optical microscope observations and COMSOL simulations reveal that lithium remains securely anchored within the scaffold, a result of the rapid mass/charge transfer and uniform electric field distribution. Consequently, this electrode achieves a remarkable DOD of 87.1% at 10 mA cm-2 for 40 mAh cm-2. Notably, when coupled with a polysulfide cathode, the constructed flexible Li/Li13Sn5@CC||Li2S6/SnO2@CC pouch cell delivers a high-areal capacity of 5.04 mAh cm-2 and an impressive areal-energy density of 10.6 mWh cm-2. The findings pave the way toward the development of high-performance LMAs, ideal for long-lasting wearable electronics.