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Improvement of the Elevated Temperature Cycling of LiMn2O4 spinel for Li Ion Batteries

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Title
Improvement of the Elevated Temperature Cycling of LiMn2O4 spinel for Li Ion Batteries
Author
Woo, Seung Hee
Advisor
Lee, Kyu Tae
Issue Date
2013-02
Publisher
Graduate School of UNIST
Abstract
Lithium manganese oxide spinel materials have been extensively studied as a cathode material for lithium ion batteries because it is inexpensive, safe, and eco-friendly. One critical shortcoming for this material is, however, the poor cycle stability that is mainly associated with manganese dissolution during extended cycling, especially at elevated temperature (> 50 oC). To relieve the capacity fading of LiMn2O4/graphite cells caused by manganese dissolution, we develop the functional binder and separator having ion exchangeability between dissolved Mn ions and Na ions of functional materials. First of all, three ion-exchangeable binders including carboxymethyl cellulose sodium salt (CMC), poly(sodium 4-styrenesulfonate) (PSS), and alginic acid sodium salt (AGA) are compared with the conventional binder of polyvinylidene fluoride (PVdF). From the galvanostatic experiments of LiMn2O4/graphite full cells at high temperature (60 oC), the ion-exchangeable binders for graphite anode show a noticeable improvement in the capacity retention. This is attributed to that the dissolved Mn ions are trapped in the ion exchangeable binders due to ion exchange between manganese ions in electrolytes and sodium ions of binders. In other words, the ion-exchangeable binders prevent the reduction of dissolved Mn ions at the surface of graphite anode, resulting in the improvement of cycle performance. This is supported by the analysis using inductively coupled plasma mass spectrometry (ICP-MS) for Mn-dissolved electrolytes and X-ray diffraction (XRD) for lithiated graphite anode. Also, the effect of ion exchange is further examined using an ion exchangeable separator. The surface-modified separator shows the improved cycle retention of LiMn2O4/graphite full cell at 60 oC due to ion exchange between manganese ions in electrolytes and sodium ions of separators.
Description
Battery Science & Technology
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