A high performance composite separator with robust environmental stability for dendrite-free lithium metal batteries

Innovative Separator Engineering: Hydrogen Bond-Driven Layer-By-Layer Assembly for Enhanced Stability and Efficiency in Lithium Metal Batteries

Lithium metal batteries (LMBs) face critical challenges due to uncontrolled lithium dendrite growth and inhomogeneous Li+ flux, largely attributed to conventional separators' poor interfacial compatibility. To address this, we propose a hydrogen bond-driven layer-by-layer (LbL) assembly strategy for engineering functional separators using poly(vinyl alcohol) (PVA) and tannic acid (TA). The optimized PP/(TA/PVA)15 separator leverages the synergistic interplay between PVA's hydroxyl groups and TA's carbonyl moieties, forming a robust hydrogen-bonded network that simultaneously enhances lithiophilicity, regulates Li+ flux uniformity, and immobilizes anions. The interfacial design achieves exceptional electrochemical performance: Li//Li symmetric cells maintain stable operation for 800 h at 0.5 mA cm-2/0.5 mAh cm-2, while Li//LiFePO4 half cells retain 73.8% capacity after 1000 cycles at 5C (decay rate: 0.026% per cycle). The separator further exhibits high ionic conductivity (0.94 mS cm-1) and Li+ transference number (0.63), outperforming conventional polyolefin counterparts. By integrating simplicity, scalability, and eco-friendliness, this work pioneers a universal interface chemistry paradigm for next-generation LMBs, offering transformative insights into separator engineering through molecular-level hydrogen-bonding control.

Regulated solvation structure and solid electrolyte interfaces via imidazolium ionic gel electrolytes with high Li-ion transference number for Li-metal batteries

Solid lithium metal batteries (LMBs) are faced with problems such as the solvation structure of lithium ion and the instability of solid electrolyte interface (SEI), which lead to poor cycling stability and anode interface damage. Here, the introduced 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMIM][FSI]) ionic liquid (IL) interacts strongly with Lithium salt to form a new ionic gel electrolyte (IGE) based on the poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), which facilitates the excellent Li-ion transference number up to 0.506 and improves the mechanical properties. The reconstruction of Li-ion solvation environment by [EMIM][FSI] and PVDF-HFP functional groups, as well as the formation of SEI protective layer rich in LiF and Li3N, make the IGE with excellent electrochemical properties and interfacial stability. As a result, the Li||Li symmetric batteries demonstrate outstanding cycle stability, while the LiFePO4||Li batteries exhibit a superior capacity of 154.04 mAh/g at 0.2 C, maintaining a capacity retention rate as high as 94.5 % even after 200 cycles. The results not only demonstrate a new approach to improve Li-ion transference number in IGEs, but also open a potential avenue to achieve LMBs with high performance.

Organic-Inorganic Dual-Network Composite Separators for Lithium Metal Batteries

The suboptimal ionic conductivity of commercial polyolefin separators exacerbates uncontrolled lithium dendrite formation, deteriorating lithium metal battery performance and posing safety hazards. To address this challenge, a novel organic-inorganic composite separator designed is prepared to enhance ion transport and effectively suppress dendrite growth. This separator features a thermally stable, highly porous poly(m-phenylene isophthalamide) (PMIA) electrospun membrane, coated with ultralong hydroxyapatite (HAP) nanowires that promote "ion flow redistribution." The synergistic effects of the nitrogen atoms in PMIA and the hydroxyl groups in HAP hinder anion transport while facilitating efficient Li+ conduction. Meanwhile, the optimized unilateral pore structure ensures uniform ion transport. These results show that the 19 µm-thick HAP/PMIA composite separator achieves remarkable ionic conductivity (0.68 mS cm-1) and a high lithium-ion transference number (0.51). Lithium symmetric cells using HAP/PMIA separators exhibit a lifespan exceeding 1000 h with low polarization, significantly outperforming commercial polypropylene separators. Furthermore, this separator enables LiFePO4||Li cells to achieve an enhanced retention of 97.3% after 200 cycles at 1 C and demonstrates impressive rate capability with a discharge capacity of 72.7 mAh g-1 at 15 C.

Functional Separator with Poly(Acrylic Acid)-Enabled Li2CO3-Free Garnet Coating for Long-Cycling Lithium Metal Batteries

Lithium metal batteries (LMBs) possess a theoretical energy density far surpassing that of commercial lithium-ion batteries (LIBs), positioning them as one of the most promising next-generation energy storage systems. Modifying separators with composite coatings comprising oxide solid-state electrolyte (SSE) particles and polymers can improve the cycling stability and safety of LMBs. However, exposure to air forms Li2CO3 on oxide SSE particles, diminishing their ion flux regulation at the electrode/electrolyte interface. Utilizing the reaction of Li2CO3 with polyacrylic acid (PAA) to form lithium polyacrylate (LiPAA), an ultra-thin composite coating on polyethylene (PE) separator with Li2CO3-free Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles and LiPAA binder is fabricated in one step. The exposed Li2CO3-free LLZTO surface increases the ionic conductivity and lithium ion (Li+) transference number of the functional separator, resulting in small resistance and uniform Li deposition of the Li metal anode. Consequently, the Li//LiCoO2 cell with the functional separator exhibits a significantly improved life of 980 cycles with 80.9% capacity retention under lean-electrolyte conditions. Both the Li//LiCoO2 coin cell and pouch cell using thin Li foil anode demonstrate good cycling stability and high mechanical robustness. This study provides a green and scalable approach for fabricating advanced separators for LMBs.

Multiple uniform lithium-ion transport channels in Li6.4La3Zr1.4Ta0.6O12/Ce(OH)3 modified polypropylene composite separator for high-performance lithium metal batteries

Lithium (Li) metal anodes (LMAs) are regarded as leading technology for advanced-generation batteries due to their high theoretical capacity and favorable redox potential. However, the practical integration of LMAs into high-energy rechargeable batteries is hindered by the challenge of Li dendrite growth. In this work, nanoparticles of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) loaded with Ce(OH)3 (LLZTCO) were designed and synthesized by a hydrothermal method. A functional composite separator was crafted by coating one side of a polypropylene (PP) separator with a composite electrolyte comprised of polyvinylidene fluoride (PVDF) and LLZTCO. The synergistic interactions between PVDF and LLZTCO provide numerous rapid lithium-ion (Li+) channels, facilitating the efficient redistribution of disparate Li+ flux originating from the insulated PP separator. The composite separator demonstrated an ionic conductivity (σ) of 3.68 × 10-3 S cm-1, substantial Li+ transference number (t+) of 0.73, and a high electrochemical window of 4.8 V at 25℃. Furthermore, the Li/LLZTCO@PP/Li symmetric cells demonstrated stable cycling for over 2000 h without significant dendrite formation. The Li/LiFePO4 (LFP) cells assembled with LLZTCO@PP separators exhibited a capacity retention of 91.6 % after 400 cycles at 1C. This study offers a practical approach to fabricating composite separators with enhanced safety and superior electrochemical performance.

Pre-oxidized and composite strategy greatly boosts performance of polyacrylonitrile/LLZO nanofibers for lithium-metal batteries

The active cyano-group in polyacrylonitrile has severe passivation of lithium anode under larger current density, which restricts the wide application of polyacrylonitrile(PAN) in lithium metal batteries. Herein, in order to address the excessive passivation of lithium metal by PAN, inspired by the pre-oxidation of carbon fibers, PAN was pre-oxidized at 230 °C, which transformed part of the cyano group into a more chemically stable cyclized structure. The electrochemical and mechanical properties of the composite solid electrolyte were effectively improved by introducing the fast ionic conductor Li6.25La3Zr2Al0.25O12 into PAN by electrospinning. The oxidized PAN-based composite solid electrolyte presents high ionic conductivity (3.05 × 10-3 S·cm-1) and high lithium transference number of 0.79 at 25 °C, further contributing to a high electrochemical window (5.3 V). The solid-state batteries assembled by Li||10 wt%-LLZAO@230-oxy-PAN||NCM523 behave superb electrochemical performance, delivering a high initial discharge capacity of 157 mAh g-1 at 0.2 C. After 100 cycles, the capacity retention was 93.3 %, indicating the electrolyte displays great electrochemical stability. This work provides new insights into the structural design of polymer-based high-voltage batteries.