| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 101 === In this study, we used PEDGE, DGEBA and D2000 by cross-linking to synthesis the copolymer –poly(ethylene oxide)-co-poly(propylene oxide) (P(EO-co-PO)). Immersing the polymer film into the organic electrolyte for 24 hours, then we got the gel polymer electrolyte (GPE). Took this GPE film to assemble batteries and test its performance. Compare the difference between GPE and the organic liquid electrolyte battery (LE) , find out the advantages of GPE.
Compare to LE, the proposed GPE has higher ionic conductivity (3.8210-3 S cm-1 at 30 °C) and a wider electrochemical voltage range (5V). Besides, P(EO-co-PO) copolymer equipped better Lithium ion dissociation ability and higher transfer number (0.7). This high GPE transference number decreases electrode polarization caused by anion accumulation and suppresses the concentration gradient to facilitate lithium ion transport. That made the electrolyte-electrode surface of GPE more stable than LE with lower resistance. Therefore, the performance can be better at higher C-rate charge-discharge test and long-term stability.
For battery performance test, we use LiFePO4-cathode and Graphite-anode to assemble the full-cell and compare the difference between GPE and LE. At lower C-rates, the discharge capacity is similar and the value is about 125mAh g-1. When discharge rate is higher than 10 C-rate, the performance decrease dramatically in LE full-cell, while GPE full-cell maintain the capacity even at 17C-rate. For long-term test, we conducted charge-discharge measurement at 1C-rate for 450 cycles. After 450 cycles the capacity retention maintained at ca. 77%. It’s better than the LE full-cell which kept only ca. 44%.
Due to the bad performance at higher C-rates by using Graphite-anode, in this study, we also developed hydrothermal method to synthesis TiO2 nanotube. TiO2 is nontoxic, high chemical stability and low price. Moreover, the nanotube structure can help to catch the electrolyte into the tube, increase the electrolyte-electrode contact surface and decrease the distance of lithium ion diffusion. And then decrease the diffusion resistance, that resulted in a discharge capacity 70 mAh g-1 at 60C-rate.
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