리튬이차전지용 양극, 음극, 고분자 전해질 소재 설계 및 특성에 관한 연구

Abstract

Si/graphite composite materials embedded with polymer microsphere as an elastic inactive phase were prepared by high-energy mechanical milling and investigated as a high capacity anode material for lithium rechargeable battery. Improved capacity retention was achieved with the composite. In situ measurement of the electrode thickness revealed that the swelling of the electrode became smaller with the increase of polymer microsphere content. It is believed that polymer microsphere played a buffering role of accommodating the mechanical strains induced by silicon expansion during lithiation, resulting in the suppression of the volume expansion of the electrode, which improved the cycle performance of the electrode.

Room temperature cross-linkable gel polymer electrolytes (GPE) were prepared by in situ cationic polymerization of tri(ethylene glycol) divinyl ether (TEGDVE) with LIBF4 that yields protonic acid and Lewis acid as an acidic initiating system by the reaction with water as an impurity in the liquid electrolyte. FT-IR analysis revealed that TEGDVE in the liquid electrolyte was successfully polymerized into gel polymer electrolyte. The resulting gel polymer electrolyte showed promising electrochemical properties including ionic conductivity, wide range in working potential and stable cycle performance as a lithium ion conducting medium.

The role of protection layer coated on cathode was described in terms of chemical and electrochemical stabilities. LiCoO2 electrode was protected by LiNi0.5Mn1.5O4 over-layer through a Gravure coating. Electrochemically inactive LiNi0.5Mn1.5O4 over-layer played an important role in stabilizing LiCoO2 surface to have less cobalt metal dissolution during high voltage and temperature electrochemical reactions, and the possible stabilization mechanism was suggested with some evidences from physicochemical analyses.