An Anode-Free Potassium-Metal Battery Enabled by a Directly Grown Graphene-Modulated Aluminum Current Collector

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.

Unraveling the Nucleation and Growth Mechanism of Potassium Metal on 3D Skeletons for Dendrite-Free Potassium Metal Batteries

Designing three-dimensional (3D) porous carbonaceous skeletons for K metal is one of the most promising strategies to inhibit dendrite growth and enhance the cycle life of potassium metal batteries. However, the nucleation and growth mechanism of K metal on 3D skeletons remains ambiguous, and the rational design of suitable K hosts still presents a significant challenge. In this study, the relationships between the binding energy of skeletons toward K and the nucleation and growth of K are systematically studied. It is found that a high binding energy can effectively decrease the nucleation barrier, reduce nucleation volume, and prevent dendrite growth, which is applied to guide the design of 3D current collectors. Density functional theory calculations show that P-doped carbon (P-carbon) exhibits the highest binding energy toward K compared to other elements (e.g., N, O). As a result, the K@P-PMCFs (P-binding porous multichannel carbon nanofibers) symmetric cell demonstrates an excellent cycle stability of 2100 h with an overpotential of 85 mV in carbonate electrolytes. Similarly, the perylene-3,4,9,10-tetracarboxylic dianhydride || K@P-PMCFs cell achieves ultralong cycle stability (85% capacity retention after 1000 cycles). This work provides a valuable reference for the rational design of 3D current collectors.

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.

Ultrastable Dendrite-Free Potassium Metal Batteries Enabled by Weakly-Solvated Electrolyte

Potassium (K) metal is considered one of the most promising anodes for potassium metal batteries (PMBs) because of its abundant and low-cost advantages but suffers from serious dendritic growth and parasitic reactions, resulting in poor cyclability, low Coulombic efficiency (CE), and safety concerns. In this work, we report a localized high-concentration electrolyte (LHCE) consisting of potassium bis(fluorosulfonyl)imide (KFSI) in a cosolvent of 1,2-dimethoxyethane (DME) and 1,1,2,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to solve the problems of PMBs. TTE as a diluent not only endows LHCE with advantages of low viscosity, good wettability, and improved conductivity but also solves the dendrite problem pertaining to K metal anodes. Using the formulation of LHCE, a CE of 98% during 800 cycles in the K||Cu cell and extremely stable cycling of over 2000 h in the K||K symmetric cell are achieved at a current density of 0.1 mA cm-2. In addition, the LHCE shows good compatibility with a Prussian Blue cathode, allowing almost 99% CE for the K||KFeIIFeIII(CN)6 full cell during 100 cycles. This promising electrolyte design realizes high-safety and energy-dense PMBs.

Low-temperature anode-free potassium metal batteries

In contrast to conventional batteries, anode-free configurations can extend cell-level energy densities closer to the theoretical limit. However, realizing alkali metal plating/stripping on a bare current collector with high reversibility is challenging, especially at low temperature, as an unstable solid-electrolyte interphase and uncontrolled dendrite growth occur more easily. Here, a low-temperature anode-free potassium (K) metal non-aqueous battery is reported. By introducing Si-O-based additives, namely polydimethylsiloxane, in a weak-solvation low-concentration electrolyte of 0.4 M potassium hexafluorophosphate in 1,2-dimethoxyethane, the in situ formed potassiophilic interface enables uniform K deposition, and offers K||Cu cells with an average K plating/stripping Coulombic efficiency of 99.80% at -40 °C. Consequently, anode-free Cu||prepotassiated 3,4,9,10-perylene-tetracarboxylicacid-dianhydride full batteries achieve stable cycling with a high specific energy of 152 Wh kg-1 based on the total mass of the negative and positive electrodes at 0.2 C (26 mA g-1) charge/discharge and -40 °C.

Spatially Confined Silver Nanoparticles in Mercapto Metal-Organic Frameworks to Compartmentalize Li Deposition Toward Anode-Free Lithium Metal Batteries

As the promising next-generation energy storage solution, lithium metal battery (LMB) has gained great attention but still suffers from troubles associated with the highly active metallic lithium. Herein, it is aimed to develop an anode-free LMB engaging no Li disk or foil by modifying the Cu current collector with mercapto metal-organic frameworks (MOFs) impregnating Ag nanoparticles (NPs). While the polar mercapto groups facilitate and guide Li+ transport, the highly lithiophilic Ag NPs help to enhance the electric conductivity and lower the energy barrier of Li nucleation. Furthermore, the MOF pores allow compartmentalizing bulk Li into a 3D matrix Li storage so that not only the local current density is reduced, but also is the plating/stripping reversibility greatly enhanced. As a result, full cells pairing the prelithiated Ag@Zr-DMBD/Cu anodes with LiFePO4 cathodes demonstrate a high initial specific capacity of 159.8 mAh g-1 , first-cycle Coulombic efficiency of 96.6%, and long-term cycling stability over 1000 cycles with 99.3% capacity retention at 1 C. This study underlines the multi-aspect functionalization of MOFs to impart lithiophilicity, polarity, and porosity to achieve reversible Li plating/stripping and paves the way for realizing high-performance anode-free LMBs through exquisite modification of the Cu current collector.

Electrospun carbon-based nanomaterials for next-generation potassium batteries

Rechargeable potassium (K) batteries that are of low cost, with high energy densities and long cycle lives have attracted tremendous interest in affordable and large-scale energy storage. However, the large size of the K-ion leads to sluggish reaction kinetics and causes a large volume variation during the ion insertion/extraction processes, thus hindering the utilization of active electrode materials, triggering a serious structural collapse, and deteriorating the cycling performance. Therefore, the exploration of suitable materials/hosts that can reversibly and sustainably accommodate K-ions and host K metals are urgently needed. Electrospun carbon-based materials have been extensively studied as electrode/host materials for rechargeable K batteries owing to their designable structures, tunable composition, hierarchical pores, high conductivity, large surface areas, and good flexibility. Here, we present the recent developments in electrospun CNF-based nanomaterials for various K batteries (e.g., K-ion batteries, K metal batteries, K-chalcogen batteries), including their fabrication methods, structural modulation, and electrochemical performance. This Feature Article is expected to offer guidelines for the rational design of novel electrospun electrodes for the next-generation K batteries.

Bifunctional Alloy/Solid-Electrolyte Interphase Layer for Enhanced Potassium Metal Batteries Via Prepassivation

Potassium (K) metal batteries have attracted great attention owing to their low price, widespread distribution, and comparable energy density. However, the arbitrary dendrite growth and side reactions of K metal are attributed to high environmental sensitivity, which is the Achilles' heel of its commercial development. Interface engineering between the current collector and K metal can tailor the surface properties for K-ion flux accommodation, dendrite growth inhibition, parasitic reaction suppression, etc. We have designed bifunctional layers via prepassivation, which can be recognized as an O/F-rich Sn-K alloy and a preformed solid-electrolyte interphase (SEI) layer. This Sn-K alloy with high substrate-related binding energy and Fermi level demonstrates strong potassiophilicity to homogeneously guide K metal deposition. Simultaneously, the preformed SEI layer can effectually eliminate side reactions initially, which is beneficial for the spatially and temporally KF-rich SEI layer on K metal. K metal deposition and protection can be implemented by the bifunctional layers, delivering great performance with a low nucleation overpotential of 0.066 V, a high average Coulombic efficiency of 99.1%, and durable stability of more than 900 h (1 mA cm-2, 1 mAh cm-2). Furthermore, the high-voltage platform, energy, and power densities of K metal batteries can be realized with a conventional Prussian blue analogue cathode. This work provides a paradigm to passivate fragile interfaces for alkali metal anodes.

Direct-Chemical Vapor Deposition-Enabled Graphene for Emerging Energy Storage: Versatility, Essentiality, and Possibility

The direct chemical vapor deposition (CVD) technique has stimulated an enormous scientific and industrial interest to enable the conformal growth of graphene over multifarious substrates, which readily bypasses tedious transfer procedure and empowers innovative materials paradigm. Compared to the prevailing graphene materials (i.e., reduced graphene oxide and liquid-phase exfoliated graphene), the direct-CVD-enabled graphene harnesses appealing structural advantages and physicochemical properties, accordingly playing a pivotal role in the realm of electrochemical energy storage. Despite conspicuous progress achieved in this frontier, a comprehensive overview is still lacking by far and the synthesis-structure-property-application nexus of direct-CVD-enabled graphene remains elusive. In this topical review, rather than simply compiling the state-of-the-art advancements, the versatile roles of direct-CVD-enabled graphene are itemized as (i) modificator, (ii) cultivator, (iii) defender, and (iv) decider. Furthermore, essential effects on the performance optimization are elucidated, with an emphasis on fundamental properties and underlying mechanisms. At the end, perspectives with respect to the material production and device fabrication are sketched, aiming to navigate the future development of direct-CVD-enabled graphene en-route toward pragmatic energy applications and beyond.