Effect of pore structure in polymer membrane from various preparation techniques on cyclic stability of 4.9 V LiNi0.5Mn1.5O4 at elevated temperature

Abstract

Pore structure of the membrane which was determined by the preparation techniques played a key role in its thermal stability and electrochemical properties. Two of the most common fabrication techniques, phase inversion and electrospinning, were used to obtain the porous polymer membrane employing poly (methyl methacrylate-butyl acrylate-acrylonitrile-styrene) (P(MMA-BA-AN-St)) as the polymer matrix. Scanning electron microscopy suggested that the morphology of polymer membranes was different: a loose and porous structure was obtained by phase inversion method, while a compact and interconnected structure with stacked and interlaced fiber filaments was prepared through electrospinning technique. Two different membranes exhibited a little discrepancy in the physical property and electrochemical performance under room temperature. However, under the elevated temperature, the pore structure of membrane prepared by phase inversion method was unstable and the mechanical strength was sharply decreased, while the electrospinning membrane maintained the original pore structure and better mechanical strength. Subsequently, the discharge capacity of the Li/LiNi0.5Mn1.5O4 cell using the electrospinning membrane kept 82% of its initial capacity after 80 cycles at 60 °C, while the phase inversion membrane only retained 10% of capacity under the same condition. Thus, the matched polymer membrane from electrospinning technique was suggested to effectively improve the cyclic stability of 4.9 V LiNi0.5Mn1.5O4 cathode under elevated temperature. This fundamental research revealed that the pore structure of the polymer membrane played a decisive role in the cycle performance of the high-energy density Li-ion battery, suggesting that the more attention should be paid particularly to the preparation technique of the membrane, in addition to designing novel polymer materials.