Poly(ethylene oxide)-co-Poly(propylene oxide)-Based Gel Electrolyte with High Ionic Conductivity and Mechanical Integrity for Lithium-Ion Batteries

摘要

Using gel polymer electrolytes (GPEs) for lithium-ion batteries usually encounters the drawback of poor mechanical integrity of the GPEs. This study demonstrates the outstanding performance of a GPE consisting of a commercial membrane (Celgard) incorporated with a poly(ethylene oxide)-co-poly(propylene oxide) copolymer (P(EO-co-PO)) swelled by a liquid electrolyte (LE) of 1 M IiPF6 in carbonate solvents. The proposed GPE stably holds LE with an amount that is three times that of the Celgard-P(EO-co-PO) composite. This GPE has a higher ionic conductivity (2.8 × 10~(-3) and 5.1 × 10~(-4) S cm~(-1) at 30 and —20 °C, respectively) and a wider electrochemical voltage range (5.1 V) than the LE-swelled Celgard because of the strong ion-solvation power of P(EO-co-PO). The active ion-solvation role of P(EO-co-PO) also suppresses the formation of the solid—electrolyte interphase layer. When assembling the GPE in a Li/LiFePO4 battery, the P(EO-co-PO) network hinders anionic transport, producing a high Li~+ transference number of 0.5 and decreased the polarization overpotential. The Li/GPE/LiFePO4 battery delivers a discharge capacity of 156-135 mAh g~(-1) between 0.1 and I C-rates, which is approximately 5% higher than that of the Li/LE/LiFePO4 battery. The IR drop of the Li/GPE/LiFePO4 battery was 44% smaller than that of the Li/LE/LiFePO4. The Li/GPE/LiFePO4 battery is more stable, with only a 1.2% capacity decay for ISO galvanostatic charge—discharge cycles. The advantages of the proposed GPE are its high stability, conductivity, Li~+ transference number, and mechanical integrity, which allow for the assembly of GPE-based batteries readily scalable to industrial levels.