The polyvinyl acetal based polymer membranes have been prepared via a phase inversion method using our own synthetic polyvinyl butyral (PVB) from polyvinyl alcohol (PVA) as the polymer matrix. The proportion of hydroxyl group in PVB is controlled using acid modification initially, and the appropriate polyurethane reaction occurs between the residual hydroxyl group of PVB and the crosslinking agent 4,4'-diphenylmethane diisocyanate (MDI) to approach three-dimensional network structure, which contributes to the chemical stability of PVB based membrane in LiFP6-based liquid electrolyte. The dense polymer membranes show a high liquid uptake of 288% and a high mechanical strength of 16.33 MPa. The membranes adsorb and swell electrolyte to form stable membrane supporting gel polymer electrolytes (GPEs), which delivers excellent performance including high ionic conductivity of 4.09 x 10(-4) Scm(-1) at room temperature, wide electrochemical window of 1.6-5.0 V (vs. Li/Li+) and good compatibility with a LiFePO4 electrode. (C) 2014 Elsevier B.V. All rights reserved