Key Takeaways & Executive Findings
- •• Amino functionalization narrows the Ti-MOF pore size to ~0.8 nm, enabling size-sieving to completely block polysulfide shuttling. • Electrostatic adsorption by positively charged amino groups redistributes and reutilizes blocked polysulfides, enhancing active material utilization. • Lewis acid-base interaction between amino and lithium ions creates transfer channels, ensuring unimpeded Li+ migration. • The modified separator achieves an ultralow capacity decay of 0.045% per cycle over 1000 cycles at 1.0C, demonstrating superior long-term stability.
Abstract
Shuttle effect of polysulfides overshadows the superiorities of lithium–sulfur batteries. Size–sieving effect could address this thorny trouble rely on size differ in polysulfides and lithium ions. However, clogged polysulfides pose some challenges for cathode and are rarely recycled during charging/discharging. Herein, an amino functionalized titanium-organic framework is designed for modifying lithium–sulfur batteries separator to address the aforementioned challenges. Wherein, the introduction of amino narrows titanium–organic framework pore size, enabling functional separator to selectively modulate lithium ions and polysulfides migration using size-sieving effect, thereby completely suppressing polysulfides shuttle. Furthermore, the blocked polysulfides will be adsorbed on the separator surface by positively charged amino leveraging electrostatic adsorption, ensuring polysulfides to redistribute and reuse, and boosting active materials utilization. Significantly, the migration of lithium ions is not hindered since there are lithium ions transfer channels formed via Lewis acid–base interaction with the help of amino. Combined with these virtues, the lithium–sulfur batteries with amino functionalized titanium-organic framework modified separator enjoy an ultralow attenuation rate of 0.045% per cycle over 1000 cycles at 1.0C. Electrostatic adsorption and Lewis acid–base interaction cover deficiencies existing in the inhibition of polysulfides shuttle by size-sieving effect, providing fresh insight into the advancement of lithium-sulfur batteries.
1. Introduction
The energy crisis is driving us to look for novel, clean energy storage devices [1–3]. Rechargeable lithium–sulfur (Li–S) batteries have held considerable promise as next–generation high–energy–storage batteries owing to the superiorities of sulfur cathode [4, 5]. Cooperated with Li, sulfur can deliver ultra–high theoretical energy densities (2800 Wh kg−1) and superior theoretical capacity (1675 mAh g−1) [6, 7]. Regrettably, the development of Li–S batteries is plagued by a series of issues caused the “shuttle effect” of polysulfides, such as continuous depletion of sulfur and self–discharging [8, 9]. Also, polysulfides that traverse the macropores of polypropylene (PP) separator would adhere to lithium metal surface, resulting in corrosion and passivation [10, 11]. This ultimately leaves rapid capacity fading and a shorter cycle lifespan of Li–S batteries [12, 13]. Therefore, it is imperative to suppress polysulfides migration for perfectly delivering the merits of Li–S batteries.
Although commercial separator that features wealthy pore architecture ensures Li+ migration during charging/discharging, the larger pore size is impossible to block the shuttle of polysulfides [14, 15]. Considering the difference in size of solvated polysulfides and Li+, exploiting functionalized coating to regulate selectively ion migrations in separators, that is, employing size–sieving effect, is a straightforward and effective approach to inhibit the shuttling of polysulfides. Delightfully, the size-sieving effect is highly effective in inhibiting polysulfides shuttle without hampering Li+ transport. Whereas, it should be stressed that the ion–selective channel of separator modified layer is supposed to be around 0.8 nm, which has been verified in our previous work [16, 17]. Therefore, selecting the appropriate materials to modify separator is a critical step.
Metal–organic framework (MOF), as uniquely porous materials characterized by well–defined and adjustable pore sizes and tunable surface chemistry, enable selectively separate various ions and molecules [18, 19]. Such as 2D zeolitic imidazolate framework films are used for highly permeable selective H2 separation [20], and functionalized UiO–66–(X)2 membrane could high–selectively separate monovalent and divalent cations [21]. Additionally, a novel MOF–gel film, as a permselective separator, is employed to restrain adverse reactions of soluble intermediates, which achieves a much longer cycle life of rechargeable organic batteries [22]. Undeniably, this brilliant selective separation ability of MOF also exerts an unsurpassed role in controlling the selective migration of ions in Li–S batteries. The affluent sub-nanometer pore size inhibits polysulfides shuttle firstly using size–sieving effect if MOF is employed as separator modified layer, and even pore structure is also favorable for
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Xiaoya Kang, Tianqi He, Hao Dang, Xiangye Li, Yumeng Wang, Fuliang Zhu, Fen Ran (2025). Designing Amino Functionalized Titanium-Organic Framework on Separators Toward Sieving and Redistribution of Polysulfides in Lithium-Sulfur Batteries. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01733-0
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Frequently Asked Questions
What is the main challenge in lithium-sulfur batteries addressed by this research?
The main challenge is the 'shuttle effect' of polysulfides, which causes capacity fading and short cycle life. The research introduces an amino-functionalized titanium-organic framework (Ti-MOF) on the separator to inhibit polysulfide shuttling via size-sieving and electrostatic adsorption.
How does the amino functionalization improve the separator performance?
Amino functionalization narrows the MOF pore size to about 0.8 nm, enabling size-sieving to block polysulfides while allowing Li+ transport. Additionally, positively charged amino groups electrostatically adsorb blocked polysulfides, promoting their redistribution and reuse, and Lewis acid-base interaction facilitates Li+ transfer.
What is the significance of the 0.8 nm pore size?
The 0.8 nm pore size is critical because it is smaller than solvated polysulfides but larger than Li+, allowing selective sieving: polysulfides are blocked while Li+ can pass through, effectively suppressing the shuttle effect without hindering ion transport.
What performance improvement was achieved with the modified separator?
The lithium-sulfur batteries with the amino-functionalized Ti-MOF modified separator exhibited an ultralow capacity decay rate of 0.045% per cycle over 1000 cycles at 1.0C, indicating excellent long-term cycling stability.
What are the key mechanisms behind the improved battery performance?
The key mechanisms are size-sieving effect (pore size exclusion), electrostatic adsorption (positively charged amino groups attract polysulfides), and Lewis acid-base interaction (amino groups interact with Li+ to form transfer channels). These work synergistically to suppress polysulfide shuttling and enhance active material utilization.
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