Currently liquid electrolyte having good ion-conductivity and high electrochemical stability has been used for the lithium secondary battery. But it has been reported there was a serious problem in the high temperature stability. In this study, the development of PVA-CN cyanoethyl polyvinyl alcohol additive which is used in lithium secondary battery electrolyte was carried out with two steps; the first step was the dissolution of PVA raw materials, and the second step was the synthesis of PVA-CN. The thermal property of the prepared PVA-CN was quantitatively analyzed using TGA. The significantly improved thermal stability of the electrolytes containing PVA-CN additives was also confirmed by monitoring swelling behavior of the membranes at high temperature, i.e. 29% less swelling effect, although they exhibited slightly lower ion conductivity, about 6% lower than commercially available electrolytes. This finding clearly suggests the possibility of preventing the swelling issue at high temperature which is the main cause of dangerous accidents from secondary battery systems.

현재 리튬이차전지에는 이온전도도나 전기화학적 안정성이 좋은 액체 전해액을 사용하고 있으나, 고온 열적안정성에 문제가 노출되고 있다. 본 연구에서는 전해액의 열 안정성을 향상시키기 위해 리튬이차전지 전해액용 cyanoethyl polyvinyl alcohol(PVA-CN) 첨가제를 합성하였으며, 합성은 polyvinyl alcohol(PVA) 원료를 용해하는 공정(Step 1)과 PVA-CN을 합성하는 공정(Step 2)으로 나누어서 진행하였다. 합성된 PVA-CN 첨가제의 열적 안정성을 확인하기 위하여 TGA 측정을 진행하였다. 전기적 특성평가에서 PVA-CN이 첨가된 전해액의 이온전도도가 기존 상용의 전해액보다 약 6% 감소하였다. 하지만, PVA-CN 첨가된 전해액을 활용한 리튬이차전지는 고온에서 swelling 특성이 매우 우수한 결과, 즉 29%의 swelling 감소 효과를 보여주었으며, 리튬이차전지의 가장 큰 사고 원인인 고온 swelling 문제를 해결할 수 있다는 결과를 얻었다.

Keywords: lithium secondary battery, electrolyte additive, high temperature safety, swelling