Jakob Heier

MXenes are promising candidates for electrochemical energy storage and conversion due to their high surface area, conductivity, and tunable surface chemistry. Among them, double transition metal MXenes exhibit the dual functionality of two transition metals (DTM), resulting in more synergistic effects. These DTMs are typically exfoliated with concentrated HF for prolonged periods, which hinders their effective use. Here, we report HF-free low-temperature molten salt synthesis of recently discovered Mo2Nb2C3Tx MXene. Exfoliated MXene was found to exhibit significantly increased interlayer spacing and larger flake size compared to MXene synthesized through traditional HF etching. The electrochemical performance of these exfoliated MXenes was assessed in acidic, basic, and neutral electrolytes. It was observed that MXene electrodes showed superior performance when tested in H2SO4 electrolyte, achieving a specific capacitance of 436 F·g−1. Notably, the symmetric cell fabricated in H2SO4 electrolyte demonstrated a unique pseudocapacitive storage behavior, where electrochemical double-layer capacitance (EDLC) dominated, resulting in a gravimetric capacitance of 200 F·g−1. This work highlights the promise of HF-free, scalable synthesis of MXenes, which significantly accelerates production times while retaining or enhancing electrochemical performance, making it a viable option for large-scale energy storage applications.

Progress in sulfur cathodes and separator interlayers has substantially curtailed polysulfide shuttling and sluggish kinetics in Li-S batteries. However, the instability of lithium metal anodes remains a major barrier to commercialization. Replacing lithium with mature lithiated graphite is attractive, but ether-based electrolytes used in Li-S cells induce Li⁺/solvent co-intercalation and rapid failure of graphite electrodes. Building optimized interlayers and sulfur cathodes, this study focuses on making graphite fully compatible with ether electrolytes (DOL/DME). By systematically adjusting the lithium-salt concentration and LiNO3 additive, we found a finely tuned compositional regime in which the graphite electrode is free from solvent co-intercalation without markedly impairing cathode kinetics. This enabled the integration of an H-TiO₂/S cathode, a thin freestanding PVDF/MS interlayer, and a lithiated graphite anode into a full cell, which delivered 1066 mAh⋅gsulfur⁻¹ at 0.1 C (N/P = 0.87). The resulting prototype demonstrates that Li-S chemistry can operate without a lithium-metal anode, offering a practical route toward safer and more commercially viable Li-S batteries.

Lithium–sulfur (Li–S) batteries suffer from rapid capacity fading due to the polysulfide (LiPS) shuttle, sluggish redox kinetics, and the formation of insulating discharge products. Here, we report a dual-engineering strategy that integrates a hydrogen-treated hollow TiO₂ (H–TiO₂) sulfur host with conductive poly­(vinylidene fluoride) (PVDF)-based MXene–TMO interlayers. Hydrogen treatment introduces Ti³⁺/oxygen vacancies and forms a hollow framework, imparting enhanced conductivity to TiO₂ while providing abundant active sites for sulfur immobilization and redox catalysis. Complementarily, the best-performing MXene–TMO interlayer, PVDF/MXene–SnO₂ (PV–MS), couples the high conductivity of MXene with the polar, catalytic activity of SnO₂, enabling efficient LiPS adsorption and accelerated conversion. This synergy yields substantial performance improvements: LiPS charge-transfer resistance decreases by 93% (4.5 to 0.31 Ω), cycling stability is significantly enhanced (capacity retention >81% compared with 64% for the reference cell), Li⁺ diffusion rates nearly double, and fast kinetic reactions are maintained even at high scan rates without diffusion limitations. Additionally, the rate capability remains robust at high current densities. Density functional theory (DFT) calculations further confirm this synergistic behavior, showing that the adsorption free energy of Li₂S₆ follows the trend |ΔG _ads|H–TiO₂ > |ΔG _ads|TiO₂ > |ΔG _ads|_graphene, indicating the strongest LiPS binding and the highest catalytic reactivity on H–TiO₂ surfaces. Both DFT and XPS analyses reveal a distinct dual-site binding mechanism in H–TiO₂, where Ti–S and Ti–O–Li interactions cooperatively enhance polysulfide anchoring, promote faster redox conversion, and improve sulfur utilization. To the best of our knowledge, this is the first demonstration of a dual-engineered Li–S cathode system in which defect-mediated sulfur hosts and catalytic interlayers operate synergistically. The resulting mechanismcontrolled sulfur release at the cathode, shuttle suppression at the interlayer, and rapid electron/ion transport across the interface, establishes a powerful design guideline for achieving long-lived and high-rate Li–S batteries.

In the pursuit of durable lithium–sulfur (Li–S) batteries, considerable research has been devoted to extending cycle life by developing advanced cathode materials. However, there exists a common overcharging problem which leads to the disfunction of Li–S batteries but has been largely overlooked. This study systematically investigates the overcharging failure and its underlying mechanisms. Experimental results reveal that failure comes from a soft internal short circuit (ISCs) caused by excessive lithium dendrite growth, primarily driven by the sulfur cathode rather than the lithium anode. Electrochemical processes during overcharging are examined, revealing the generation of a specific by‐product. By analyzing the structural properties of the sulfur cathode such as topography and pore connectivity, and through combined experiments and theoretical simulations, the complex mechanisms through which the cathode influences lithium dendrite growth are elucidated. Finally, an effective "interlayer" strategy is proposed to mitigate the overcharging failure. This work sheds light on the overcharging mechanisms and emphasizes the critical importance of cathode design in improving the safety and reliability of Li–S batteries.

Lithium‐sulfur (Li–S) batteries offer exceptional theoretical energy density, yet their practical realization remains limited by polysulfide shuttling and sluggish redox kinetics. Conventional interlayers typically mitigate only one of these bottlenecks, either improving conductivity or providing polysulfide adsorption, which proves insufficient under realistic conditions. Here, we introduce a multifunctional interlayer composed of electrospun polyvinylidene fluoride (PVDF) nanofibers embedded with MXene/transition metal oxide (TMO) hybrids and compacted via hot pressing. This design uniquely integrates MXene’s conductivity, TMO’s strong polar–polar adsorption and catalytic activity, and PVDF’s structural flexibility, producing a single architecture capable of suppressing shuttle effects, accelerating LiPS conversion, and stabilizing the electrode‐interlayer interface. Electrochemical evaluation demonstrates high discharge capacities of 1032 mAh g ⁻¹ for PVDF‐calcined MXene (P‐CM) interlayer and 931 mAh g ⁻¹ for PVDF‐MXene/SnO ₂ (P‐MS) interlayer at medium sulfur loading (2–3 mg cm ⁻² ), with outstanding long‐term retention of 800 mAh g ⁻¹ after 100 cycles and ultralow fading rates of 0.23% and 0.18% per cycle. Strikingly, at high sulfur loadings (5–6 mg cm ⁻² ), both interlayers sustained similarly low decay rates (0.18% per cycle), highlighting their robustness under practical conditions. Electrochemical impedance spectroscopy revealed a > 94% reduction in polysulfide shuttle resistance, directly confirming the efficient immobilization and conversion of soluble lithium polysulfides (LiPSs). Moreover, Li   ⁺ diffusion coefficients were boosted to 9.89 × 10 ⁻⁸ mg cm ² s ⁻¹ , nearly two orders of magnitude higher than previously reported values, while postmortem X‐ray photoelectron spectrometer (XPS) identified Sn–S, Sn–O, and S–Ti–C bonding as evidence of strong chemical interactions. This work presents the first electrospun PVDF‐based interlayer integrating MXene/TMO hybrids, establishing a multifunctional strategy that concurrently resolves shuttling and redox kinetics limitations. The ability to maintain high stability at practical sulfur loadings, coupled with scalable electrospinning and hot‐pressing fabrication, underscores its potential for enabling next‐generation Li–S batteries.

Poor cycling stability in lithium–sulfur (Li–S) batteries necessitates advanced electrode/electrolyte design and innovative interlayer architectures. Heterogeneous catalysis has emerged as a promising approach, leveraging the adsorption and catalytic performance on lithium polysulfides (LiPSs) to inhibit LiPSs shuttling and improve redox kinetics. In this study, we report an ultrathin and laminar SnO₂@MXene heterostructure interlayer (SnO₂@MX), where SnO₂ quantum dots (QDs) are uniformly distributed across the MXene layer. The combined structure of SnO₂ QDs and MXene, along with the creation of numerous active boundary sites with coordination electron environments, plays a critical role in manipulating the catalytic kinetics of sulfur species. The Li–S cell with the SnO₂@MX-modified separator not only demonstrates superior electrochemical performance compared to cells with a bare separator but also induces homogeneous Li deposition during cycling. As a result, an areal capacity of 7.6 mAh cm⁻² under a sulfur loading of 7.5 mg cm⁻² and a high stability over 500 cycles are achieved. Our work demonstrates a feasible strategy of utilizing a laminar separator interlayer for advanced Li–S batteries awaiting commercialization and may shed light on the understanding of heterostructure catalysis with enhanced reaction kinetics.

MXene inks are promising alternatives for conventional conductive inks in printing electronics. However, the formulation of MXene inks is challenging due to the physicochemical properties of the few solvents in which MXenes can be dispersed. Furthermore, conventional MXene dispersions form high‐viscosity gels at low concentrations, making their ink formulation even more difficult. Here, a novel co‐solvent‐based approach is reported for dispersing MXenes in polar organic solvents that have excellent physicochemical properties as a carrier solvent for ink formulation but are not suitable for dispersing MXenes. Water is used as a dispersing agent and the second component of the co‐solvent system. The surfactant‐like role of water in dispersing MXenes in such solvents is also confirmed using molecular dynamics simulations. Using this strategy, the sol‐gel transition is significantly upshifted, enabling the formulation of highly concentrated inks with single‐ or few‐layered large‐flake MXenes. Numerous types of electronic components such as interconnects, resistors, transparent flexible conductive electrodes, and micro‐supercapacitors are fabricated using high‐throughput coating and printing techniques such as gravure printing, showcasing the immense potential of MXene inks for room‐temperature printing of electronics.