Polyolefin-Based Separator with Interfacial Chemistry Regulation for Robust Potassium Metal Batteries

Thiosalicylic-Acid-Mediated Coordination Structure of Nickel Center via Thermodynamic Modulation for Aqueous Ni-Zn Batteries

Uniquely functional nanocomplexes with rich coordination environments are critical in energy storage. However, the construction of structurally versatile nanocomplexes remains challenging. In this study, a nickel-based complex with structural variations is designed via thermodynamic modulation using a dual-ligand synthesis strategy. A nickel-based nanomaterial (NiSA-SSA-160) with a large specific surface area is synthesized around the competing coordination of the host and guest molecules that differ in terms of the chemical properties of the O and S elements. Concurrently, the coordination environment of NiSA-SSA-160 is investigated via X-ray absorption fine structure spectroscopy. The thiol functional groups synergistically induced an electron-rich Ni structure, thus increasing the electron density of the central atom. The electrochemical performance of an assembled NiSA-SSA-160//Zn@CC battery is shown to improve significantly, with a maximum energy density of 0.54 mWh cm-2 and a peak power density of 49.49 mW cm-2. This study provides a new perspective regarding coordination transformations and offers an idea for the design of functionally rich nanomaterials.

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.

Tunable Interfacial Electric Field-Mediated Cobalt-Doped FeSe/Fe3Se4 Heterostructure for High-Efficiency Potassium Storage

The interfacial electric field (IEF) in the heterostructure can accelerate electron transport and ion migration, thereby enhancing the electrochemical performance of potassium-ion batteries (PIBs). Nevertheless, the quantification and modulation of the IEF for high-efficiency PIB anodes currently remains a blank slate. Herein, we achieve for the first time the quantification and tuning of IEF via amorphous carbon-coated undifferentiated cobalt-doped FeSe/Fe3Se4 heterostructure (denoted UN-CoFe4Se5/C) for efficient potassium storage. Co doping can increase the IEF in FeSe/Fe3Se4, thereby improving the electron transport, promoting the potassium adsorption capacity, and lowering the diffusion barrier. As expected, the IEF magnitude in UN-CoFe4Se5/C is experimentally quantified as 62.84 mV, which is 3.65 times larger than that of amorphous carbon-coated FeSe/Fe3Se4 heterostructure (Fe4Se5/C). Benefiting from the strong IEF, UN-CoFe4Se5/C as a PIB anode exhibits superior rate capability (145.8 mAh g-1 at 10.0 A g-1) and long cycle lifespan (capacity retention of 95.1 % over 3000 cycles at 1.0 A g-1). Furthermore, this undifferentiated doping strategy can universally regulate the IEF magnitude in CoSe2/Co9Se8 and FeS2/Fe7S8 heterostructures. This work can provide fundamental insights into the design of advanced PIB electrodes.

Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

Chloro-Functionalized Ether-Based Electrolyte for High-Voltage and Stable Potassium-Ion Batteries

Ether-based electrolyte is beneficial to obtaining good low-temperature performance and high ionic conductivity in potassium ion batteries. However, the dilute ether-based electrolytes usually result in ion-solvent co-intercalation of graphite, poor cycling stability, and hard to withstand high voltage cathodes above 4.0 V. To address the aforementioned issues, an electron-withdrawing group (chloro-substitution) was introduced to regulate the solid-electrolyte interphase (SEI) and enhance the oxidative stability of ether-based electrolytes. The dilute (~0.91 M) chloro-functionalized ether-based electrolyte not only facilitates the formation of homogeneous dual halides-based SEI, but also effectively suppress aluminum corrosion at high voltage. Using this functionalized electrolyte, the K||graphite cell exhibits a stability of 700 cycles, the K||Prussian blue (PB) cell (4.3 V) delivers a stability of 500 cycles, and the PB||graphite full-cell reveals a long stability of 6000 cycles with a high average Coulombic efficiency of 99.98 %. Additionally, the PB||graphite full-cell can operate under a wide temperature range from -5 °C to 45 °C. This work highlights the positive impact of electrolyte functionalization on the electrochemical performance, providing a bright future of ether-based electrolytes application for long-lasting, wide-temperature, and high Coulombic efficiency PIBs and beyond.

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.

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.