Polarity-tuned Gel Polymer Electrolyte Coating of High-voltage LiCoO2 Cathode Materials
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- Polarity-tuned Gel Polymer Electrolyte Coating of High-voltage LiCoO2 Cathode Materials
- Park, Jang-Hoon; Cho, Ju-Hyun; Kim, Jong-Su; Shim, Eun-Gi; Lee, Yun-Sung; Lee, Sang-Young
- Lithium-ion batteries; High-voltage lithium cobalt oxide; Polarity; Gel polymer electrolyte coating; Polyimide; Ethylene-vinyl acetate copolymer
- Issue Date
- 전기화학회지, v.14, no.2, pp.117 - 124
- We demonstrate a new surface modification of high-voltage lithium cobalt oxide (tex:\small\textstyle$LiCoO_2$) cathode active materials for lithium-ion batteries. This approach is based on exploitation of a polarity-tuned gel polymer electrolyte (GPE) coating. Herein, two contrast polymers having different polarity are chosen: polyimide (PI) synthesized from thermally curing 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid (as a polar GPE) and ethylene-vinyl acetate copolymer (EVA) containing 12 wt% vinyl acetate repeating unit (as a less polar GPE). The strong affinity of polyamic acid for tex:\small\textstyle$LiCoO_2$ allows the resulting PI coating layer to present a highly-continuous surface film of nanometer thickness. On the other hand, the less polar EVA coating layer is poorly deposited onto the tex:\small\textstyle$LiCoO_2$, resulting in a locally agglomerated morphology with relatively high thickness. Based on the characterization of GPE coating layers, their structural difference on the electrochemical performance and thermal stability of high-voltage (herein, 4.4 V) tex:\small\textstyle$LiCoO_2$ is thoroughly investigated. In comparison to the EVA coating layer, the PI coating layer is effective in preventing the direct exposure of tex:\small\textstyle$LiCoO_2$ to liquid electrolyte, which thus plays a viable role in improving the high-voltage cell performance and mitigating the interfacial exothermic reaction between the charged tex:\small\textstyle$LiCoO_2$ and liquid electrolytes.
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