![]() Porosity is a significant feature of a separator. Last, due to their low melting points, the polyolefin separators suffer thermal shrinkage at elevated temperatures 10, 11. First, due to their intrinsic hydrophobicity and low surface energy, they provide low wettability and durability in liquid electrolytes which contain polar solvents. Although the polyolefin separators are effective for portable electronic devices, they suffer two major disadvantages. Their properties such as crystallinity, porosity, thickness, electrolyte adsorption, chemical, mechanical and thermal stability etc., however, could be changed at long or extreme operating conditions such as severe temperatures. The multi-layer separator such as PP-PE-PP trilayer laminates has been patented as a high heat-resistant separator which provides adequate thermal and chemical stability and mechanical strength 2, 9, 10, 11. Most separators available in the market are porous polyolefin materials composed of polyethylene (PE) 4, 5 and polypropylene (PP) membranes with thickness less than 25 μm 6, 7, 8 due to their high stability and low cost. Particularly, their porous structure plays a vital role to determine battery performance. On the other hand, separators, made up of polymer membranes, separating cathode and anode electrodes, acting as an electrolyte reservoir and assisting the transport of ions 2, 3, can also strongly affects the cell performance. Most of the studies working on Li-ion batteries that aiming at the applications in the utility storage or transportations focuses on developing low-cost electrode materials with high capacity, long cycle life and best safety 1. In the recent era, the demand even increased intensively due to their wide applications in the industrial usage of electrical vehicle and power storage systems. Lithium-ion batteries (LIBs) is a key module in portable consumer electronics. Therefore, designing a new separator material with a more compact crystalline structure or surface modification to reduce the Li insertion during the battery operation is desirable. The calculations revealed that the insertion of Li-ion and EC molecule into PP or PE are thermodynamically favourable process which might explain the anomalous significant lattice expansion during the low current density charging. ![]() Density functional theory calculations were used to investigate the mechanism responsible for the irregular results. High-resolution scanning electron microscopy is employed to witness the pore changes of the trilayered membrane. The capacity fading and the resistance value of the cell measured at 0.025 C (5th retention, 92%) is unexpectedly larger than that at 1.0 C (5th retention, 97.3%) from the electrochemical impedance spectroscopic data. Significant lattice changes of both PP and PE were found during the low current density charging. ![]() The abnormal lattice expansion of commercial polypropylene (PP)/polyethylene (PE)/polypropylene (PP) separator in lithium-ion battery under different charging current densities was observed by in-situ X-ray diffraction. ![]()
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