多相半结晶PVDF / PEO / LiClO 4固体聚合物电解质的主要取决于链节弛豫的离子电导率,Electrochimica Acta

固体聚合物电解质（SPE）膜包含聚偏二氟乙烯（PVDF）/聚环氧乙烷（PEO）共混物（75/25 wt / wt％）作为主体聚合物基质，高氯酸锂（LiClO 4）作为离子掺杂剂对于不同的盐浓度（即5、10、15、20、25和30 wt％），以及PVDF / PEO共混物的重量比也有所变化（即75 / 25、50 / 50、25 / 75和10 / 90 wt / wt％）和浓度为25 wt％的LiClO 4通过在70°C下进行溶液浇铸来制备。通过X射线衍射（XRD）和傅立叶变换红外（FTIR）光谱获得的结果表明，PVDF的α和β相晶体以及PEO晶体的尺寸和含量发生了巨大变化。这些SPE材料的结晶度随盐浓度和聚合物共混物组成的变化而变化。在27°C下从20 Hz到1 MHz的频率范围内使用介电弛豫谱（DRS）来研究SPE膜的复阻抗，介电常数，介电损耗角正切，交流电导率和电模量谱。通过新颖的“主曲线表示”程序分别并同时分析了所有这些光谱，以揭示各种介电极化过程（即电极，界面，分子（偶极）和离子）的贡献及其随增加而表现出的弛豫在这些异质离子导电材料中，其频率为大约1阶，并且与相邻过程基本重叠。这些材料的损耗角正切光谱显示出明显的介电弛豫峰，其归因于阳离子配位的聚合物链段动力学。所有这些材料的高频交流电导率数据均遵循幂定律，而阻抗数据的奈奎斯特图则显示了盐浓度≥20wt％的电解质的可区分的体积和电极极化频率区域。在弛豫时间和直流离子电导率之间观察到的反相关关系表明，离子的传输主要与聚合物链段运动相关，这有助于离子-偶极子络合物中有利的导电位点之间的跳跃。当盐浓度≤15 wt％时，SPE膜相对较硬，并且具有较高的结晶度，并且与具有盐浓度的较软和较低结晶度的膜相比，它们具有明显的介电，直流离子电导率和弛豫性能≥20wt％。这些SPE膜具有良好的电化学性能和接近统一的总离子转移数。在这两套SPE膜中，最大直流离子电导率为2.01×10 75PVDF / 25PEO–30 wt％LiClO 4膜在27°C下为-5 S / cm，来自不同盐浓度的薄膜 为25PVDF / 75PEO–25 wt％LiClO 4膜为5.61×10 -6 S / cm聚合物共混物基质的一组不同组成。这些SPE膜在环境温度下具有相当高的离子电导率值，以及它们有希望的电化学性能，也证实了它们是适合开发固态可充电锂离子电池的新型离子导体。

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The solid polymer electrolyte (SPE) films comprise poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO) blend (75/25 wt/wt%) as host polymer matrix with lithium perchlorate (LiClO4) as ionic dopant for different salt concentrations (i.e., 5, 10, 15, 20, 25, and 30 wt%), and also varying compositional weight ratio PVDF/PEO blends (i.e., 75/25, 50/50, 25/75, and 10/90 wt/wt%) with 25 wt% concentration of LiClO4 were prepared by solution casting at 70 °C. The results obtained from X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that there is an enormous alteration in the α- and β-phase crystals of the PVDF and the size and content of the PEO crystallites, and also the degree of crystallinity of these SPE materials with the variation of salt concentration and the polymer blend composition. Dielectric relaxation spectroscopy (DRS) was employed over the frequency range from 20 Hz to 1 MHz, at 27 °C for the study of the complex impedance, dielectric permittivity, dielectric loss tangent, ac electrical conductivity, and electric modulus spectra of the SPE films. All these spectra were analyzed separately and simultaneously by a novel ‘master curve representation’ procedure to unveil the contribution of various dielectric polarization processes (i.e., electrode, interfacial, molecular (dipolar), and the ionic) and their relaxations which are exhibited with increasing order of frequency and have substantial overlapping with the adjacent processes in these heterogeneous ion conducting materials. The loss tangent spectra of these materials manifest prominent dielectric relaxation peak which attributes to the cation coordinated polymer chain segmental dynamics. The high frequencies ac electrical conductivity data of all these materials obey the power law, whereas the Nyquist plots of impedance data exhibit reasonably distinguishable bulk and electrode polarization frequency regions for the electrolytes having salt concentration ≥20 wt%. The inverse correlation observed between the relaxation time and the dc ionic conductivity establishes that the transportation of ions is predominantly coupled to the polymer chain segmental motion which assists the hopping between favourable conduction sites in the ion-dipole complexes. The SPE films are comparatively stiffer and have a slightly higher degree of crystallinity when the salt concentration is ≤ 15 wt% and they exhibit distinct dielectric, dc ionic conductivity, and relaxation behaviour as compared to that of the softer and lower crystallinity films having salt concentration ≥20 wt%. These SPE films possess good electrochemical performance and close-to-unity total ion transference number. Among these two sets of the SPE films, the maximum dc ionic conductivity was noted 2.01 × 10−5 S/cm at 27 °C for the 75PVDF/25PEO–30 wt% LiClO4 film from the set of different salt concentrations, and 5.61 × 10−6 S/cm for 25PVDF/75PEO–25 wt% LiClO4 film from the set of varying compositions of the polymer blend matrix. The considerable ionic conductivity values of these SPE films at ambient temperature and also their promising electrochemical performance corroborate them as novel ion conductors suitable for the development of solid-state rechargeable lithium-ion batteries.