A Dielectric MXene-Induced Self-Built Electric Field in Polymer Electrolyte Triggering Fast Lithium-Ion Transport and High-Voltage Cycling Stability.

Quasi-solid polymer electrolyte (QPE) lithium (Li)-metal battery holds significant promise in the application of high-energy-density batteries, yet it suffers from low ionic conductivity and poor oxidation stability. Herein, a novel self-built electric field (SBEF) strategy is proposed to enhance Li+ transportation and accelerate the degradation dynamics of carbon-fluorine bond cleavage in LiTFSI by optimizing the termination of MXene. Among them, the SBEF induced by dielectric Nb4C3F2 MXene effectively constructs highly conductive LiF-enriched SEI and CEI stable interfaces, moreover, enhances the electrochemical performance of the QPE. The related Li-ion transfer mechanism and dual-reinforced stable interface are thoroughly investigated using ab initio molecular dynamics, COMSOL, XPS depth profiling, and ToF-SIMS. This comprehensive approach results in a high conductivity of 1.34 mS cm-1, leading to a small polarization of approximately 25 mV for Li//Li symmetric cell after 6000 h. Furthermore, it enables a prolonged cycle life at a high voltage of up to 4.6 V. Overall, this work not only broadens the application of MXene for QPE but also inspires the great potential of the self-built electric field in QPE-based high-voltage batteries.

Separator Engineering Based on Cl-Terminated MXene Ink: Enhancing Li+ Diffusion Kinetics with a Highly Stable Double-Halide Solid Electrolyte Interphase.

Separator engineering is a promising route to designing advanced lithium (Li) metal anodes for high-performance Li metal batteries (LMBs). Conventional separators are incapable of regulating the Li+ diffusion across the solid electrolyte interphase (SEI), leading to severe dendritic deposition. To address this issue, a polypropylene (PP) separator modified by spray coating the Cl-terminated titanium carbonitride MXene ink is designed (PP@Ti3CNCl2). The lithiophilic MXene provides excellent electrolyte wettability and low Li+ diffusion barriers, finally enhancing the Li+ diffusion kinetics of excessively stable SEI. The X-ray photoelectron spectroscopy depth profiling as well as cryo-transmission electron microscopy reveals that a gradient SEI hierarchy with evenly distributed LiF and LiCl is spontaneously formed during the electrochemical process. As a consequence, PP@Ti3CNCl2 delivers a high Coulombic efficiency (99.15%) coupled with a prolonged lifespan of over 5500 h in half cells and 3100 cycles at 2 C in full cells. This work offers an effective strategy for constructing dendrite-free and Li+ permeable interfaces toward high-energy-density LMBs.

Enabling Scalable Polymer Electrolyte with Dual-Reinforced Stable Interface for 4.5 V Lithium-Metal Batteries.

Hitherto, it remains a great challenge to stabilize electrolyte-electrode interfaces and impede lithium dendrite proliferation in lithium-metal batteries with high-capacity nickel-rich LiNx Coy Mn1- x-y O2 (NCM) layer cathodes. Herein, a special molecular-level-designed polymer electrolyte is prepared by the copolymerization of hexafluorobutyl acrylate and methylene bisacrylamide to construct dual-reinforced stable interfaces. Verified by X-ray photoelectron spectroscopy depth profiling, there are favorable solid electrolyte interphase (SEI) layers on Li metal anodes and robust cathode electrolyte interphase (CEI) on Ni-rich cathodes. The SEI enriched in lithiophilic N-(C)3 guides the homogenous distribution of Li+ and facilitates the transport of Li+ through LiF and Li3 N, promoting uniform Li+ plating and stripping. Moreover, the CEI with antioxidative amide groups can suppress the parasitic reactions between cathode and electrolyte and the structural degradation of cathode. Meanwhile, a unique two-stage rheology-tuning UV polymerization strategy is utilized, which is quite suited for continuous electrolyte fabrication with environmental friendliness. The fabricated polymer electrolyte exhibits a high ionic conductivity of 1.01 mS cm-1 at room temperature. 4.5 V NCM622//Li batteries achieve prolonged operation with a retention rate of 85.0% after 500 cycles at 0.5 C. This work provides new insights into molecular design and processibility design for polymer-based high-voltage batteries.

Realizing Scalable Nano-SiO2-Aerogel-Reinforced Composite Polymer Electrolytes with High Ionic Conductivity via Rheology-Tuning UV Polymerization.

Polymer electrolytes for lithium metal batteries have aroused widespread interest because of their flexibility and excellent processability. However, the low ambient ionic conductivity and conventional fabrication process hinder their large-scale application. Herein, a novel polyethylene-oxide-based composite polymer electrolyte is designed and fabricated by introducing nano-SiO2 aerogel as an inorganic filler. The Lewis acid-base interaction between SiO2 and anions from Li salts facilitates the dissociation of Li+. Moreover, the SiO2 interacts with ether oxygen (EO) groups, which weakens the interaction between Li+ and EO groups. This synergistic effect produces more free Li+ in the electrolyte. Additionally, the facile rheology-tuning UV polymerization method achieves continuous coating and has potential for scalable fabrication. The composite polymer electrolyte exhibits high ambient ionic conductivity (0.68 mS cm-1) and mechanical properties (e.g., the elastic modulus of 150 MPa). Stable lithium plating/stripping for 1400 h in Li//Li symmetrical cells at 0.1 mA cm-2 is achieved. Furthermore, LiFePO4//Li full cells deliver superior discharge capacity (153 mAh g-1 at 0.5 C) and cycling stability (with a retention rate of 92.3% at 0.5 C after 250 cycles) at ambient temperature. This work provides a promising strategy for polymer-based lithium metal batteries.

Enabling Scalable Polymer Electrolyte with Synergetic Ion Conductive Channels via a Two Stage Rheology Tuning UV Polymerization Strategy.

Lithium metal batteries with polyethylene oxide (PEO) electrolytes are considered as one of the ideal candidates for next generation power sources. However, the low ambient operation capability and conventional solvent-based fabrication process of PEO limit their large-scale application. In this work, a comb-like quasi-solid polymer electrolyte (QPE) reinforced with polyethylene glycol terephthalate nonwoven is fabricated. Combining the density functional theory calculation analysis and polymer structure design, optimized and synergized ion conductive channels are established by copolymerization of tetrahydrofurfuryl acrylate and introduction of plasticizer tetramethyl urea. Additionally, a unique two-stage solventless UV polymerization strategy is utilized for rheology tuning and electrolyte fabrication. Compared with the conventional one-step UV process, this strategy is ideally suited for the roll-to-roll continuous coating fabrication process with environmental friendliness. The fabricated QPE exhibits high ionic conductivity of 0.40 mS cm-1 and Li+ transference number (t = 0.77) at room temperature. LiFePO4 //Li batteries are assembled to evaluate battery performance, which deliver excellent discharge capacity (144.9 mAh g-1 at 0.5 C) and cycling stability (with the retention rate 94.5% at 0.5 C after 200 cycles) at room temperature. The results demonstrate that it has high potential for solid-state lithium metal batteries.