전기방사 기술을 이용한 리튬-이온 배터리용 전극 제조 및 전기화학적 특성

Abstract

리튬-이온 배터리는 높은 에너지밀도, 낮은 자가방전, 그리고 긴 수명을 가지므로 작게는 소형 전자장비부터 크게는 스마트 그리드의 동력원으로 쓰일 수 있는 차세대 저장장치이다. 하지만 현재 개발 되어있는 리튬-이온 배터리는 상당수가 코발트를 사용하는데 코발트가 고가이기 때문에 생산단가를 줄이기 위해서 대체 물질에 대한 연구가 활발히 진행 중이다. 또한 스마트 그리드의 에너지 원으로 쓰기 위해서는 높은 에너지 밀도에 못지않게 높은 출력밀도도 요구한다. 출력밀도는 리튬 이온의 시간당 이동량과 관계가 있으며, 전극과 전해질 사이의 비표면적이 넓을수록 출력밀도가 높아진다. 비표면적을 높이기 위해 본 연구에서는 전기방사 기술 (electrospinning)을 사용하였으며, 리튬과 코발트에 니켈을 추가하여 리튬-니켈-코발트 옥사이드 나노 웹을 만들었다. 나노 웹 제작은 니켈-코발트 옥사이드 나노 웹에 리튬염을 첨가하여 리튬-니켈-코발트 옥사이드 전극을 만드는 방법과 리튬-니켈-코발트 전구체를 이용하여 리튬-니켈-코발트 옥사이드 전극을 만드는 방법을 사용하였다. 제작된 전극의 분석을 위해 전자 주사 현미경 (FE-SEM)을 사용하였으며, 제작된 전극이 각각 평균 150 nm와 350 nm의 직경을 가지는 것을 확인하였다. 또한 열 중량 분석 (TGA)을 통해 리튬-니켈-코발트 옥사이드 나노 웹을 합성하는 온도를 설정하였으며, X-ray 회절 분석 (XRD)를 통해 만들어진 물질의 성분이 두 조건 모두 LiNi0.7Co0.3O2가 합성된 것을 확인하였다. 그리고 대시간 전위 변화를 통해 0.2 C-rate의 방전조건에서 니켈-코발트 옥사이드에 리튬염을 도핑한 리튬-니켈-코발트 옥사이드 나노 웹으로 만든 전극은 102.3 mAh/g, 리튬-니켈-코발트 전구체를 이용하여 만든 리튬-니켈-코발트 옥사이드 나노 웹으로 만든 전극은 133.4 mAh/g의 비축전용량을 나타내는 것을 확인하였으며, 이 결과로 니켈-코발트 옥사이드에 리튬염을 도핑하여 제작한 리튬-니켈-코발트 옥사이드 나노 웹 전극보다 리튬-니켈-코발트 전구체를 이용하여 제작한 리튬-니켈-코발트 옥사이드 나노 웹 전극이 더 우수한 성능이 가지는 것을 확인하였다.|Lithium-ion battery is a next-generation energy storage which can be applied in various fields from compact electronic devices to power source of smart-grid because of its high energy density, low self-discharge and long life cycles. However, most of currently developed lithium-ion battery includes a relatively expensive material, like a cobalt, thus many attempts have been made to develop alternative materials to decrease the unit cost of production. To be utilized in a power source of smart-grid, lithium-ion battery requires not only high energy density but also high power density. Power density is related with the amount of lithium-ion movement per hour and the surface area of the battery electrode. In this research, an electrospinning technique was used to fabricate lithium-nickel-cobalt oxide nano-web with high specific surface area. Two methods were tried to fabricate lithium-nickel-cobalt nano-web electrode. In the case of first method, lithium salt was added into the electrospun nickel-cobalt oxide nano-web (dLNCO). For the second method, lithium, nickel, cobalt precursors were mixed together into a solution and it was electrospun to form lithium-nickel-cobalt nano-web (LNCO). The morphology of the dLNCO and LNCO nano-webs was investigated by scanning electron microscope (FE-SEM), and each nano-web showed 150 nm and 350 nm of average diameter, respectively. Thermogravimetric analysis (TGA) was performed to determine an adequate temperature for the synthesis of lithium-nickel-cobalt oxide nano-web. X-ray diffraction (XRD) analysis confirmed that the both nano-webs were LiNi0.7Co0.3O2. Chronopotentiometry (CD) was performed to measure the specific capacity of the dLNCO and LNCO electrodes, which exhibited 102.3 and 133.4 mAh/g at 0.2 C-rate, respectively. As a result, the lithium-nickel-cobalt oxide nano-web electrode (LNCO) fabricated using a lithium-nickel-cobalt precursor showed higher performance than the electrode (dLNCO) prepared by doping a lithium salt on nickel-cobalt oxide nano-web.; Lithium-ion battery is a next-generation energy storage which can be applied in various fields from compact electronic devices to power source of smart-grid because of its high energy density, low self-discharge and long life cycles. However, most of currently developed lithium-ion battery includes a relatively expensive material, like a cobalt, thus many attempts have been made to develop alternative materials to decrease the unit cost of production. To be utilized in a power source of smart-grid, lithium-ion battery requires not only high energy density but also high power density. Power density is related with the amount of lithium-ion movement per hour and the surface area of the battery electrode. In this research, an electrospinning technique was used to fabricate lithium-nickel-cobalt oxide nano-web with high specific surface area. Two methods were tried to fabricate lithium-nickel-cobalt nano-web electrode. In the case of first method, lithium salt was added into the electrospun nickel-cobalt oxide nano-web (dLNCO). For the second method, lithium, nickel, cobalt precursors were mixed together into a solution and it was electrospun to form lithium-nickel-cobalt nano-web (LNCO). The morphology of the dLNCO and LNCO nano-webs was investigated by scanning electron microscope (FE-SEM), and each nano-web showed 150 nm and 350 nm of average diameter, respectively. Thermogravimetric analysis (TGA) was performed to determine an adequate temperature for the synthesis of lithium-nickel-cobalt oxide nano-web. X-ray diffraction (XRD) analysis confirmed that the both nano-webs were LiNi0.7Co0.3O2. Chronopotentiometry (CD) was performed to measure the specific capacity of the dLNCO and LNCO electrodes, which exhibited 102.3 and 133.4 mAh/g at 0.2 C-rate, respectively. As a result, the lithium-nickel-cobalt oxide nano-web electrode (LNCO) fabricated using a lithium-nickel-cobalt precursor showed higher performance than the electrode (dLNCO) prepared by doping a lithium salt on nickel-cobalt oxide nano-web.