海南大学海南大学余凤副教授和佛山科学技术陈永教授，CEJ：凝胶聚合物电解质的结构设计提高锂电池界面稳定性

凝胶聚合物电解质的结构设计提高锂电池界面稳定性

在锂金属电池中，电解质作为与锂金属直接接触的成分，它们所产生的电极/电解质界面的性质与电解质的成分密切相关，同时对于锂金属的稳定性有着很大的影响。然而，传统的液态有机电解质电压窗口低，热稳定性差，不利于锂金属电池的应用。近年来，凝胶电解质已成为研究的焦点，其具有相对液态电解质较高的电压窗口，较强的机械性能，同时又拥有比全固态电解质更优异的离子电导率。

锂离子溶剂化结构对于电极/电解质界面结构及组成影响深远。然而，目前大多数研究都关注与新型凝胶电解质的开发，然而对凝胶电解质LE相的研究较少。相比纯液态电极液和固态电解质，复合凝胶电解质中多组分的相互作用会导致锂离子的配位环境相对复杂，这从而会影响到负极电解质界面生成及性能，因此对复合凝胶电解质中的锂离子传输行为和溶剂化结构研究是非常必要的。

近日，海南大学海南大学余凤副教授和佛山科学技术陈永教授合作，在国际知名期刊Chemical Engineering Journal上发表题为“A composite gel polymer electrolyte by incorporating modified POSS endowing inorganic-rich SEI formation and stable cycle life for lithium metal batteries”的文章。

作者通过在改性纤维素中共混PEG 改性的 POSS，制备了具有良好锂离子溶剂化结构的复合凝胶聚合物电解质。改性POSS的引入不仅增强了GPE的结构强度，而且诱导了以SSIPs/CIPs和AGGs为主的Li溶剂化鞘结构的形成。锂离子良好的溶剂化结构有利于生成稳定的富含LiF的SEI来抵抗锂枝晶，提高GPE的抗氧化能力和LMB的循环性能。该工作研究了有机/无机复合凝胶电解质（改性POSS/纤维素基凝胶电解质）体系下的锂离子传输行为及其对锂金属电池负极界面的影响，为有机-无机复合凝胶电解质的研究提供了有价值的思路。

要点一：克服纳米颗粒在有机基体中的积聚现象

Figure 1. (a) Schematic diagram of modification of POSS. (b) FTIR spectra of POSS, PEG and PEG-modified POSS. (c) XRD patterns of POSS and PEG-modified POSS. (d) Nuclear magnetic resonance hydrogen spectra of POSS-PEG-3 in DMSO-d6.

Figure 2. Dispersed characterization of unmodified and modified POSS. i) physical photographs, ii) SEM images, iii) elemental mapping of carbon and iv) elemental mapping of silicon for CP (a), CPP-1 (b), CPP-2 (c) and CPP-3 (d), respectively. (e) Two-dimensional (2D) Raman images of the CP (i), CPP-1 (ii), CPP-2 (iii) and CPP-3 (iv).

要点二：改性POSS对溶剂化结构的调控

Figure 3. MD simulation snapshots of (a) LE and (b) LE with modified POSS addition. The RDF g(r) and coordination numbers n(r) were calculated through MD simulations for two systems: (c) LE and (d) LE with modified POSS. Raman spectra and the proportion of free TFSI−, SSIPs/CIPs and AGGs in the CPP-0 (e), CPP-1 (f), CPP-2 (g) and CPP-3 (h) GPE systems. (i)-(j) Schematic representation of dominated Li+ solvated structures in GPE (CPP-0) and composite GPE (CPP-2) system respectively.

Figure 4. (a) LSV curves of different electrolytes at a scan rate of 1 mV s−1. (b) Theoretical calculation of LUMO and HOMO values for different solvents and solvated structures.

要点三：电池性能及机理分析

Figure 5. Cycling performances of Li||Li symmetric cells assembled with different gel polymer electrolytes. (a) Operating with a current density of 0.05 mA cm⁻², (b) Operating with a current density of 0.1 mA cm⁻².

Figure 6. Compositional and structural analyses of SEI layer. XPS spectra of interfacial constituent elements from the cyclic electrodes (C1s, Li1s, O1s and F1s) of the Li||Li symmetric cells assembled with CPP-0, 1, 2, and 3, respectively.

Figure 7. Schematic representation of anode SEI layer formation mechanism in CPP-0, CPP-2 and CPP-3 samples.

Figure 8. Electrochemical performances of Li|| LiFePO₄ coin cells assemble with different GPE. (a) Rate performances of Li|| LiFePO₄ coin cells and galvanostatic charge/discharge plots of (b) CPP-0-based and (c) CPP-2 based Li|| LiFePO₄ coin cell at different rates. (d) Cycling performances of Li|| LiFePO₄ coin cells at 0.2 C. (e) Cycling performances of Li|| LiFePO₄ coin cells at 0.5C.

https://doi.org/10.1016/j.cej.2024.149499.

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