关键词: 锂离子电池, 凝胶聚合物电解质, 非溶剂诱导相转化法, 聚氨酯, 醋酸纤维素

Abstract:

Electrolyte still has to be improved to satisfy the increasingly rigid demands of lithium ion batteries that have higher energy densities. Thermoplastic polyurethane (TPU) has two phase structures of soft segments and hard segments, which can guarantee the electrochemical and physical performances of electrolyte for lithium ion battery. It is now creatively applied to the gel polymer electrolyte matrix of lithium ion batteries. In this paper, a novel polymer membrane based on thermoplastic polyurethane/cellulose acetate (TPU/CA) was prepared by non-solvent induced phase separation (NIPS) method. Further, the TPU/CA blending gel polymer electrolyte (GPE) was prepared by absorbing liquid electrolyte. The effects of CA contents on the physical and electrochemical properties of the polymer membranes were studied. The structures, morphologies and performances of the membranes with different ratios of CA to TPU were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), differential scanning calorimetry (DSC), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The results show that the addition of CA to the blended polymer resulted in lower crystallinity of TPU and higher liquid uptake capability of electrolyte. The TPU/CA membrane possessed a large pore structure, but maintained sufficient mechanical strength. The decomposition temperature of TPU/CA samples with the weight loss of 5% was above 300℃, indicating good thermal stability of each sample. Among the TPU/CA blend electrolytes, the TPU/CA = 7/3 based electrolyte presented an ionic conductivity of 1.04 mS·cm^-1 with electrochemical stability above 5.1 V (vs. Li/Li⁺) at room temperature. The lithium ion battery with the TPU/CA = 7/3 GPE also exhibited a higher charge-discharge capacity of 150.9 mAh·g^-1 at 0.2 C, and a capacity retention rate of 95.7% at 0.5 C was confirmed after 100 cycles. All of these results demonstrate that this new TPU/CA blended gel polymer electrolyte is a promising candidate for lithium ion batteries.

Key words: lithium ion batteries, gel polymer electrolytes, non-solvent induced phase separation, thermoplastic polyurethane, cellulose acetate