A Sandwich PVDF/HEC/PVDF Gel Polymer Electrolyte for Lithium Ion Battery

- A new composite HEC-PVDF gel polymer electrolyte with sandwich-like structure is prepared.
- Its mechanical strength is largely improved compared with that of hydroxyethyl cellulose.
- Its ionic conductivity and lithium ion transference number are greatly increased.
- Li//LiFePO4 cell based this gel polymer electrolyte exhibits excellent performance.

A sandwich structure-like PVDF/HEC/PVDF polymer membrane is reported as host for matrix of gel polymer electrolytes for lithium ion batteries. The inner HEC (hydroxyethyl cellulose) layer is compact, and can avoid micro short-circuits. The producibility of the composite membrane is guaranteed due to the simple and efficient electro-spinning process for manufacturing the PVDF (poly(vinylidene fluoride)) layer and low-cost and eco-friendly HEC layer. This structure integrates the advantages of the HEC and PVDF, and it presents high uptake of liquid electrolyte (135.4%), excellent retention of liquid electrolyte, high ionic conductivity (0.88 mS cm−1 at ambient temperature), low activation energy for lithium movement (0.016 eV), and high lithium ion transference number (t+ = 0.57), all properties are superior to those of the pure HEC membrane and commercial polyolefin separator (Celgard 2730). With the PVDF/HEC/PVDF gel polymer electrolyte as the electrolyte and separator, the assembled Li//LiFePO4 cell exhibits a notably high discharge capacity (140 mAh g−1) over 140 cycles. The PVDF and HEC components are non-combustible, which is in sharp contrast with the combustible polymers for the commercial separators. These results show that this kind of sandwiched gel polymer electrolyte is promising for scale-up of lithium ion batteries especially those needing high safety and reliability.

TOC: A composite gel polymer electrolyte based on hydroxyethyl cellulose (HEC) and poly (vinylidene fluoride) (PVDF) with sandwich-like architecture exhibiting high safety, good mechanical property is prepared and characterized.203