전구체의 물성에 따른 리튬 2차전지용 Li(Ni0.5Co0.2Mn0.3)O2의 전기화학적 특성 변화
Influence of Precursor on the Electrochemical Properties of Li(Ni0.5Co0.2Mn0.3)O2 Cathode for the Lithium Secondary Battery
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초록
리튬2차전지용 양극소재인 Li(Ni0.5Co0.2Mn0.3)O2를 공침법을 이용해 Ni0.5Co0.2Mn0.3(OH)2 전구체로부터 합성하였고, 공침조건을 조절하여 전구체의 1차 입자 형상을 Flake형상과 Needle형상으로 제어하였다. 동일한 공정으로 리튬과 혼합하고 열처리하여, 입도, 탭밀도, 화학적 성분 등이 동일한 분체물성의 양극 소재를 합성하였다. 전구체의 1차입자 형상에 따른 Li(Ni0.5Co0.2Mn0.3)O2의 전기화학적 특성을 평가하고, 이 특성의 변화를 SEM, XRD, EELS로 이용하여 분석하여 연관성을 고찰하였다. Needle형상 전구체로 합성한 Li(Ni0.5Co0.2Mn0.3)O2 양극의 1차입자는 Flake형상 전구체로 합성한 경우보다 작고, EELS결과로는 입자표면의 Li농도가 내부보다 상대적으로 높았다. 전기화학적인 수명과 출력특성에서 Needle형상 전구체로 합성한 양극이 Flake형상 전구체의 경우보다 우수한 특성을 보였는데, 임피던스 측정으로부터 낮은 전하이동저항에 연관되어 있을 것으로 생각된다.
Abstract
The one of the cathode material, Li(Ni0.5Co0.2Mn0.3)O2, was synthesized by the precursor, Ni0.5Co0.2Mn0.3(OH)2, from the co-precipitation method and the morphologies of the primary particle of precursors were flake and needle-shape by controlling the precipitation parameters. Identical powder properties, such as particle size, tap density, chemical composition, were obtained by same process of lithiation and heat-treatment. The relation between electrochemical performances of Li(Ni0.5Co0.2Mn0.3)O2 and the primary particle morphology of precursors was analyzed by SEM, XRD and EELS. In the Li(Ni0.5Co0.2Mn0.3)O2 cathode from the needleshape precursor, the primary particle size was smaller than that from flake-shape precursor and high Li concentration at grain edge comparing grain center. The cycle and rate performances of the cathode from needle-shape precursor shows superior to those from flake-shape precursor, which might be attributed to low charge-transfer resistance by impedance measurement.
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