Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes
Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes
复制标题
通过嵌段聚合物混合电解质中富含均聚物的途径增强电导率
DOI：
10.1021/acs.macromol.9b01879
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发表时间：
2019
期刊：
影响因子：
5.5
通讯作者：
Epps, Thomas H.
中科院分区：
文献类型：
--
作者：
Morris, Melody A.;Sung, Seung Hyun;Ketkar, Priyanka M.;Dura, Joseph A.;Nieuwendaal, Ryan C.;Epps, Thomas H.
离子电导率和锂离子电池稳定性的优化可以通过独立地调节嵌段聚合物（BP）电解质的离子传输和机械鲁棒性来实现。然而，BP电解质的离子电导率固有地受到离子导电嵌段与机械坚固嵌段的共价连接等因素的限制。本文中，BP电解质聚苯乙烯-嵌段-聚（低聚氧乙烯基甲基丙烯酸酯）[PS-b-POEM]与不同分子量的POEM均聚物共混。引入更高分子量的均聚物添加剂（α > 1状态）促进了BP自组装内的“干刷状”均聚物分布，并导致在更移动的富含均聚物的区域中更高的锂盐浓度，相对于“湿刷状”（α < 1状态）和未共混的复合材料，其中α是共聚物中POEM均聚物和POEM嵌段之间的分子量比。中子和X射线反射计（分别为NR和XRR）提供了关于锂盐和聚合物分布的额外细节。从XRR，α > 1的共混物显示出增加的界面宽度相比，其BP（未共混）或α < 1的对应物，因为更中心的分布的均聚物。这一结果，与NR数据，表明即使在整个POEM域的盐浓度配对，意味着有一个更高的盐浓度在均聚物POEM丰富的地区在干刷共混物比在湿刷共混物。此外，使用7 Li固态核磁共振谱，我们发现了对应于锂迁移率（TLi迁移率）转变的温度，该温度是共混物类型的函数。在所有情况下，TLi迁移率均高于T39 °C。有趣的是，在α > 1的复合材料中，共混的BP的离子电导率最高，即使这些复合材料具有比α < 1的复合材料更高的Tg，这表明在α > 1的组装体中形成的富含均聚物的导电路径比在α < 1的共混物中更大的锂离子迁移率对电导率具有更大的影响。
The optimization of ionic conductivity and lithium-ion battery stability can be achieved by independently tuning the ion transport and mechanical robustness of block polymer (BP) electrolytes. However, the ionic conductivity of BP electrolytes is inherently limited by the covalent attachment of the ionically conductive block to the mechanically robust block, among other factors. Herein, the BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights. The incorporation of a higher molecular weight homopolymer additive (α > 1 state) promoted a “dry brush-like” homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the “wet brush-like” (α < 1 state) and unblended composites, where α is the molecular weight ratio between the POEM homopolymer and the POEM block in the copolymer. Neutron and X-ray reflectometry (NR and XRR, respectively) provided additional details on the lithium salt and polymer distributions. From XRR, the α > 1 blends showed increased interfacial widths in comparison to their BP (unblended) or α < 1 counterparts because of the more central distribution of the homopolymer. This result, paired with NR data that suggested even salt concentrations across the POEM domains, implied that there was a higher salt concentration in the homopolymer POEM-rich regions in the dry brush blend than in the wet brush blend. Furthermore, using7Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (TLi mobility) that was a function of blend type.TLi mobilitywas found to be 39 °C aboveTgin all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the α > 1 composites, even though these composites had higherTgs than the α < 1 composites, demonstrating that homopolymer-rich conducting pathways formed in the α > 1 assemblies had a larger influence on conductivity than the greater lithium ion mobility in the α < 1 blends.