Boosting the Oxidative Potential of Polyethylene Glycol‐Based Polymer Electrolyte to 4.36 V by Spatially Restricting Hydroxyl Groups for High‐Voltage Flexible Lithium‐Ion Battery Applications

Abstract

Cross‐linked polyethylene glycol‐based resin (c‐PEGR) is constructed by a ring‐opening reaction of polyethylene glycol diglycidyl ether (PEGDE) with epoxy groups and polyether amine (PEA) with amino groups. By confining the hydroxyl groups with inferior oxidative stability to the c‐PEGR backbone, the oxidation potential of the PEG‐based polymer material with reduced reactivity is boosted to 4.36 V. The c‐PEGR based gel electrolyte shows excellent flexibility, lithium‐ion transport, lithium compatibility, and enhanced oxidation stability, and is successfully applied to a 4.35 V lithium cobaltate (LCO)||lithium (Li) battery system. A quasi‐static linear scanning voltammetry (QS‐LSV) method is proposed for the first time to accurately measure the oxidation potential and electrochemical stability window of materials with low conductivities such as polymers, which possesses the advantages of high accuracy and short test time. This work provides new insights and research techniques for selecting polymer electrolytes for high‐voltage flexible lithium‐ion batteries (LIBs).

Are Polymer‐Based Electrolytes Ready for High‐Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

“…Floating test is an alternative method that determines the oxidative stability limit of electrolytes. [108] In the floating test, the cell is charged at a constant current up to a selected potential, and this voltage is maintained. To explore the oxidative limit of the electrolyte, the cell was progressively placed at higher voltages until the breakdown voltage is achieved.…”

“…[107] Accordingly, a higher reactivity of the terminal hydroxyls would be in agreement with the early oxidation of hydroxyls in PEO reported by Seidl et al [105] Another recent study reported higher oxidative stability for a cross-linked polymer electrolyte containing free hydroxyls compared to PEG, which was caused by the restricted mobility and reactivity of the hydroxyls in the cross-linked electrolyte. [108] The diverging results reported in the recent literature or their conflicting interpretation indicate that the evaluation of the absolute stability limit of PEO-based electrolytes is still challenging. In contrast, the relevance of this intrinsic value for battery operation is unclarified.…”

Carbon dots crosslinked gel polymer electrolytes for dendrite‐free and long‐cycle lithium metal batteries

“…For example, Yang et al 31 reported that replacing −OH with −OCH 3 could increase the ESW of the electrolytes from 4.0 to 4.3 V. As shown in Figure 2H, for the PEG‐ or CD‐incorporated composite electrolytes, the corresponding ESWs are 3.9 and 4.3 V, respectively. However, PCCEs remain stable until the voltage increases to 4.8 V. The enlarged ESW shows that the combination of PEG and CDs can effectively decrease the activity of the terminal group of CDs 32,33 and also improve the oxidation‐resistance ability of PEG 34,35 …”

“…However, PCCEs remain stable until the voltage increases to 4.8 V. The enlarged ESW shows that the combination of PEG and CDs can effectively decrease the activity of the terminal group of CDs 32,33 and also improve the oxidation-resistance ability of PEG. 34,35 Figure 2I-L shows photos of these samples. After incorporation of PEG-CDs, the color of the PVDF film changes to yellow, consistent with the color of the PEG-CDs powder.…”

Initiating a high-temperature zinc ion battery through a triazolium-based ionic liquid

“…45 As reported previously, the addition of salt can reduce the "free" solvent in the system and decrease the reactivity of the solvent, thus improving the electrochemical stability. [46][47][48] Herein, the addition of salts resulted in a broader ESW of 6.36 V for T1S-20 and 4.46 V for WS-20 (Fig. 2(b)).…”