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

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 noncombustible, 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. (C) 2017 Elsevier Ltd. All rights reserved.