서지주요정보
Li 이온 2차전지용 $LiMnO_2$ 양극의 구조 및 열적 안정성 개선을 위한 Ni, Al치환 $(LiMn_{1-x-y}Ni_xAl_yO_2)$ 에 대한 연구 = Ni and Al substitution for the structural and thermal stability of $LiMnO_2$ prepared by Sol-Gel method
서명 / 저자 Li 이온 2차전지용 $LiMnO_2$ 양극의 구조 및 열적 안정성 개선을 위한 Ni, Al치환 $(LiMn_{1-x-y}Ni_xAl_yO_2)$ 에 대한 연구 = Ni and Al substitution for the structural and thermal stability of $LiMnO_2$ prepared by Sol-Gel method / 김유민.
저자명 김유민 ; Kim, You-Min
발행사항 [대전 : 한국과학기술원, 2002].
Online Access 원문보기 원문인쇄

소장정보

등록번호

8012904

소장위치/청구기호

학술문화관(문화관) 보존서고

MMS 02013

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초록정보

Recently, orthorhombic structured $LiMnO_2$ has been studied as a potential cathode material of Li ion secondary battery. It has high theoretical capacity (285mAh/g), low cost and environmental affinity. In spite of these merits, the big obstacle to its commercialization is the phase transition, i.e. structural instability, from orthorhombic $LiMnO_2$ (Pmnm, zig-zag layered structure) to $LiMn_2O_4$ (Fd3m, spinel structure). Because $Mn^{3+}$ ions induce Jahn-Teller distortion, the orthorhombic $LiMnO_2$ with zigzag layered structure is a thermodynamically unstable phase. Furthermore, during electrochemical $Li^+$ insertion/desertion cycling, phase transition to spinel occurs due to the migration of cations; manganese ions and lithium ions migrate into the octahedral sites and tetrahedral sites in lithium layers, repectively. Orthorhombic $LiMnO_2$ has a small initial discharge capacity below 50mAh/g and needs much time to reach maximum capacity. Therefore, in order to commercialize the $LiMnO_2$ as a cathode material, phase transition must be prevented. For that purpose, $LiMnO_2$ should have a perfect-layered structure instead of the meta-stable zigzag layered structure by lowering the concentration of $Mn^{3+}$ ion in $LiMnO_2$. In this work, to reduce the concentration of $Mn^{3+}$ ions, 50at% of divalent nickel $(Ni^{2+})$ ions are substituted by using a sol-gel method, which can produce uniform and homogeneous powders. It is considered that the $LiMn_{0.5}Ni_{0.5}O_2$ powder has perfect layer structure of R-3m symmetry because all manganese ions are tetravalent. $(Mn^{4+})$ The $LiNi_{0.5}$ $Mn_{0.5}O_2$ has a discharge capacity of 100mAh/g and stable cyclic performance up to 50 cycles. By X-ray reflection diffraction (XRD) and Cyclic voltammetry (CV) analyses, it is confirmed that $LiNi_{0.5}Mn_{0.5}O_2$ shows no phase transition during electrochemical cycling. However, 50at% substitution of nickel deteriorates the thermal stability of lithium manganese oxide. Differential scanning calorimeter (DSC) analysis shows that the exothermic temperature corresponding to the oxygen evolution is lowered from 247℃ $(LiMnO_2)$ to 232℃ $(LiNi_{0.5}Mn_{0.5}O_2)$. In general, lithium nickel oxide has much less thermal stability than other cathode materials such as $LiCoO_2$ and $LiMn_2O_4$. To enhance the thermal stability, other elements, such as Al and Ti, which have the strong bonding energy with oxygen have been doped. In $LiNi_{0.5}Mn_{0.5}O_2$ small amount of Al is doped. It is found that 5at% of Al is the optimum composition. There are no second phase and capacity-fading phenomenon. Over 5at% Al, the discharge capacity faded with the formation of second phase. The first discharge capacity of $LiMn_{0.5}Ni_{0.45}Al_{0.05}O_2$ is 100mAh/g. The cyclic performance is similar to that of $LiMn_{0.5}Ni_{0.5}O_2$. finally, the thermal stability of $LiMn_{0.5}Ni+{0.45}Al_{0.05}O_2$ has increased; the exothermic temperature increases from 232 $(LiNi_{0.5}Mn_{0.5}O_2)$ to 248℃.

서지기타정보

서지기타정보
청구기호 {MMS 02013
형태사항 [v], 70 p. : 삽도 ; 26 cm
언어 한국어
일반주기 저자명의 영문표기 : You-Min Kim
지도교수의 한글표기 : 이재영
지도교수의 영문표기 : Jai-Young Lee
학위논문 학위논문(석사) - 한국과학기술원 : 재료공학과,
서지주기 참고문헌 : p. 67-70
주제 리튬 이온 이차 전지
리튬 망간 옥사이드
상전이
열적 안정성
Lithium Ion Secondary Battery
Lithium Manganese Oxide
Phase Transition
Thermal Stability
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