Palácio Gustavo, Pulcinelli Sandra H, Santilli Celso V
Chemistry Institute of the São Paulo State University, UNESP 14800-060 Araraquara São Paulo Brazil
RSC Adv. 2022 Feb 14;12(9):5225-5235. doi: 10.1039/d1ra09138g. eCollection 2022 Feb 10.
Correlations among the structure, thermal properties, and ionic conductivity of solid polymer electrolytes (SPEs) were studied using a ureasil-polyethylene oxide (U-PEO) organic-inorganic hybrid prepared according to a simple sol-gel route, employing a low molecular weight PEO macromer ( = 1900 g mol). The behavior of an amorphous sample loaded with lithium triflate (LiTFSI) at an optimum ratio between ether oxygen and lithium (EO/Li = 15) was compared with that of a semicrystalline sample prepared without salt loading. The temperature range investigated by differential scanning calorimetry (DSC), Raman spectroscopy, small angle X-ray scattering (SAXS), and complex impedance spectroscopy covered both the glass transition and the melting temperature of the U-PEO. The gauche to trans conformational transformation of the (O-C-C-O)Li sequence showed similarity between the temperature evolution of the semi-crystalline U-PEO and amorphous U-PEO:Li samples, providing an indication of the local structural memory of crystalline state in the amorphous SPE. The linear thermal expansion of the average correlation distance between the siloxane crosslink nodes and the long-distance period of the lamellar semi-crystalline edifice were determined by SAXS. Comparison of the expansion curves suggested that although the siloxane nodes were excluded from the PEO crystalline edifice, the sharp expansion of the amorphous region between the lamellae during melting permitted modulation of the free volume of the hybrid network. In addition, the temperature-induced Li-EO decomplexation observed by Raman spectroscopy explained the change of the average activation energy of the conduction process revealed by the different Arrhenius regimes. These results evidence the key role of the ionic conductivity decoupling from the segmental motion of chain pair channels on the improvement of ion mobility through the free volume between chains. This concept may inspire materials chemistry researchers to design optimized structures of polymer electrolytes with minimized structural memory of crystaline building blocks and improved ionic conductivity.
采用简单溶胶 - 凝胶法制备的脲硅 - 聚环氧乙烷（U - PEO）有机 - 无机杂化材料，使用低分子量PEO大分子单体（ = 1900 g/mol），研究了固体聚合物电解质（SPEs）的结构、热性能和离子电导率之间的相关性。将以最佳醚氧与锂比例（EO/Li = 15）负载三氟甲磺酸锂（LiTFSI）的非晶态样品的行为与未负载盐制备的半晶态样品的行为进行了比较。通过差示扫描量热法（DSC）、拉曼光谱、小角X射线散射（SAXS）和复阻抗谱研究的温度范围涵盖了U - PEO的玻璃化转变温度和熔点。（O - C - C - O）Li序列从gauche到trans的构象转变表明半晶态U - PEO和非晶态U - PEO:Li样品的温度演变具有相似性，这表明非晶态SPE中存在晶态的局部结构记忆。通过SAXS测定了硅氧烷交联节点之间平均相关距离的线性热膨胀以及层状半晶态结构的长周期。膨胀曲线的比较表明，尽管硅氧烷节点被排除在PEO晶态结构之外，但在熔化过程中层片之间非晶区的急剧膨胀允许对杂化网络的自由体积进行调制。此外，拉曼光谱观察到的温度诱导的Li - EO解络合解释了不同阿伦尼乌斯区域揭示的传导过程平均活化能的变化。这些结果证明了离子电导率与链对通道的链段运动解耦在通过链间自由体积提高离子迁移率方面的关键作用。这一概念可能会激发材料化学研究人员设计具有最小化晶态结构单元结构记忆和提高离子电导率的优化聚合物电解质结构。
