Copyright © 2022 Foshan MBRT Nanofiberlabs Technology Co., Ltd All rights reserved.Site Map
With the increasing demand for energy and growing concerns for environmental sustainability, the need for high-performance energy storage systems is on the rise. Lithium-ion batteries, known for their high energy density and long cycle life, have been widely applied. However, traditional liquid electrolytes pose safety issues. Solid polymer electrolytes (SPEs), with their good mechanical properties and safety features, are gradually emerging as an alternative. Yet, they also face challenges such as low ionic conductivity and insufficient thermal stability. In recent years, rare earth oxides like gadolinium oxide (Gd₂O₃), with their high dielectric constant and good electrochemical performance, have been used to modify polymer electrolytes.
(1) Material Preparation
Electrospinning technology was employed to fabricate poly(acrylonitrile) (PAN)/poly(ethylene glycol) (PEG) composite nanofiber electrolytes doped with gadolinium oxide (Gd₂O₃). First, Gd₂O₃ nanoparticles were synthesized via the sol–gel method. Gadolinium chloride hexahydrate (GdCl₃·6H₂O) was used as the precursor and reacted with a sodium hydroxide solution to form Gd(OH)₃, which was then dried and calcined at high temperatures to obtain high-purity Gd₂O₃ nanoparticles. Subsequently, PAN, PEG, and lithium bis(trifluoromethanesulfonimide) (LiTFSI) were dissolved in N,N-dimethylformamide (DMF) to form a uniform polymer solution. Different weight ratios (5%, 10%, 15%, and 20%) of Gd₂O₃ nanoparticles were added to the polymer solution and dispersed evenly through magnetic stirring. Finally, the mixed solution was loaded into a syringe, and composite nanofiber membranes were prepared on aluminum foil using an electrospinning machine. During the electrospinning process, an electric field strength of 10.0 kV/cm was applied, with a solution flow rate of 1.0 mL/h and a spinning duration of 5 hours. After preparation, the fiber membranes were dried in a vacuum oven at 60°C to remove residual solvents. It was found that incorporating 15% (by weight) of Gd₂O₃ nanofibers into PAN/PEG resulted in a flexible electrolyte membrane with significantly enhanced performance.
Figure 1. Electrospinning method for preparing PAN/PEG/LiTFSI/Gd₂O₃ polymer electrolytes with different ratios of Gd₂O₃ using an electrospinning device.
(2) Performance Analysis of PAN/PEG with 15% (by weight) Gd₂O₃ Nanofibers
1. Ionic Conductivity
It was discovered that when 15% (by weight) of Gd₂O₃ nanofibers were added to the PAN/PEG matrix, the resulting flexible electrolyte membrane exhibited high ionic conductivity (1.026×10⁻⁴ S cm⁻¹) at room temperature. This remarkable increase in conductivity can be attributed to the uniform distribution of Gd₂O₃ nanoparticles, which not only increased the amorphous regions in the polymer matrix but also provided more pathways for lithium-ion transport, thereby facilitating rapid ion migration.
Figure 2. (A) EIS plot for prepared polymer electrolyte at room temperature; (B) EIS of PAN/PEG/LiTFSI/Gd₂O₃ (15 wt.%) at different temperatures using an electrospinning device; (C) Temperature-dependent ionic conductivity plot [A- PAN/PEG, B- PAN/PEG/LiTFSI, C- PAN/PEG/LiTFSI/5 wt.% Gd₂O₃, D- PAN/PEG/LiTFSI/10 wt.% Gd₂O₃, E- PAN/PEG/LiTFSI/20 wt.% Gd₂O₃, and F- PAN/PEG/LiTFSI/15 wt.% Gd₂O₃]; (D) Equivalent circuit of PAN/PEG/LiTFSI/Gd₂O₃ polymer electrolyte.
2. Lithium-ion Transport
The lithium-ion transference number in the composite electrolyte reached 0.83. This high value indicates that the transport efficiency of lithium ions in the electrolyte is relatively high, which can effectively reduce polarization within the battery and thus enhance the overall performance and cycling stability of the battery.
Figure 3. Lithium-ion transference number [A- PAN/PEG, B- PAN/PEG/LiTFSI, C- PAN/PEG/LiTFSI/5 wt.% Gd₂O₃, D- PAN/PEG/LiTFSI/10 wt.% Gd₂O₃, E- PAN/PEG/LiTFSI/15 wt.% Gd₂O₃, and F- PAN/PEG/LiTFSI/20 wt.% Gd₂O₃] measured using an electrospinning machine.
3. Wide Electrochemical Window
The electrochemical stability window (ESW) is a key indicator for assessing the stability of electrolytes at different voltages. In this study, the ESW of the composite electrolyte with 15% Gd₂O₃ reached 5.5 V. This wide ESW indicates that the electrolyte can remain stable at high voltages, making it suitable for high-energy-density lithium-ion batteries and effectively preventing the decomposition of the electrolyte and side reactions within the battery at high voltages.
Figure 4. Electrochemical stability window of (A) PAN-PEG, (B) PAN-PEG-LiTFSI, (C) PAN/PEG-LiTFSI/5 wt.% Gd₂O₃, (D) PAN/PEG-LiTFSI/10 wt.% Gd₂O₃, (F) PAN/PEG-LiTFSI/15 wt.% Gd₂O₃, (E) PAN/PEG-LiTFSI/20 wt.% Gd₂O₃.
4. Good Thermal Stability
The Gd₂O₃ composite electrolyte demonstrated good thermal stability at 150°C, with no significant thermal shrinkage. This characteristic indicates that the electrolyte can maintain its structural integrity in high-temperature environments, thereby enhancing the safety and reliability of the battery and effectively preventing internal short circuits and thermal runaway in the battery caused by high temperatures.
Figure 5. Thermal shrinkage of (A) PAN, (B) PAN-PEG, (C) PAN-PEG-LiTFSI, (D) PAN/PEG-LiTFSI/5 wt.% Gd₂O₃, (E) PAN/PEG-LiTFSI/10 wt.% Gd₂O₃, (F) PAN/PEG-LiTFSI/15 wt.% Gd₂O₃, (G) PAN/PEG-LiTFSI/20 wt.% Gd₂O₃ measured using an electrospinning device.
In this study, electrospinning and in-situ polymerization were used to create a Gd₂O₃/LiTFSI/PEG/PAN composite electrolyte with a three-dimensional (3D) framework. The addition of Gd₂O₃ particles causes cyclization in order and segmenting of the PAN/PEG matrices in the electrolytes. The PAN/PEG/LiTFSI/Gd₂O₃ electrolyte, with its altered chemical structure, exhibits improved electrolyte absorption (~246%), porosity (~97%), and thermal shrinkage (150°C). Moreover, the electrochemical performance of the PAN/PEG/LiTFSI/different ratio Gd₂O₃ electrolytes was thoroughly assessed. The composite polymer electrolytes with PAN/PEG/LiTFSI/15 wt.% Gd₂O₃ had the highest conductivity at 1.026×10⁻⁴ S·cm⁻¹ at room temperature, an electrochemical window of approximately 5.5 V vs Li/Li⁺, an activation energy value of 0.23, and a Li⁺ transfer number of 0.83. A solid-state electrolyte PAN/PEG/LiTFSI/15% Gd₂O₃ electrolyte membrane demonstrated good electrochemical performance at ambient temperature. Our experimental results show that Gd₂O₃-enhanced PAN/PEG/LiTFSI-based electrolytes have the potential for use in future solid-state lithium batteries.
Electrospinning Nanofibers Article Source:
https://doi.org/10.1007/s10965-024-04243-6
