溶液法製備奈米多成份層狀陰極材料之結晶構造解析與電化學特性研究

Crystal Structure Analysis and Electrochemical Characterization of Nanosized Multicomponent Layered Cathode Materials Prepared via Soft Chemical Routes

林裕凱(Yu-Kai Lin)

指導教授 ： 呂宗昕

國立臺灣大學/工學院/化學工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.02395

摘要

本研究成孕H微乳膠法合成出奈米級高容量層狀LiNi1/3Co1/3Mn1/3O2陰極材料粉體。經800oC煆燒三小時可得晶相良好且具奈米尺度(約45 nm)的粉體。Rietveld精算及X-ray吸收光譜(XAS)的結果顯示以微乳膠法所合成之LiNi1/3Co1/3Mn1/3O2粉體具有良好的陽離子序化程度。將LiNi1/3Co1/3Mn1/3O2於2.5 V至4.5 V操作電壓區間進行室溫及高溫(55oC)充放電，其放電電容容量分別為187.2 mAh/g及195.5 mAh/g。此外以微乳膠法所合成之LiNi1/3Co1/3Mn1/3O2也具有相當少的不可逆電容量(< 6 %)以及優良的電容量維持度。由於以微乳膠法所合成之LiNi1/3Co1/3Mn1/3O2具有奈米尺度，其動力表現亦較具微米尺度的固相法LiNi1/3Co1/3Mn1/3O2粉體優良。當操作電壓上限為4.6 V時，LiNi1/3Co1/3Mn1/3O2電容量衰退情形較低操作電壓上限嚴重，此與晶格中鈷離子的氧化還原反應有關，而LiNi1/3Co1/3Mn1/3O2於4.59 V的電荷轉移阻力也較其他電位時大，其可能導致鈷離子於高電位之電荷補償不完全。

由於當操作電壓區間為2.5 V至4.6 V時，LiNi1/3Co1/3Mn1/3O2中鈷離子的氧化還原並不完全，故以溶膠凝膠法合成層狀結構LiNi1/3Co1/3Mn1/3-yAlyO2以探討鈷離子進行完整氧化還原反應時陰極材料之電化學特性。XANES圖譜顯示隨鋁添加量的增加，LiNi1/3Co1/3Mn1/3-yAlyO2中鈷的價數並不會改變，而鎳的價數卻會由2+逐漸變為3+。故LiNi1/3Co1/3Mn1/3-yAlyO2中可遷出的鋰離子會因鋁的添加而減少，但鋰離子遷出率會改善。雖然鈷離子的氧化還原於LiNi1/3Co1/3Mn1/3-yAlyO2中較為完整，但當鋁的掺雜量超過一特定範圍時，其電化學活性也會因此降低，對電荷轉移以及鈷離子的氧化還原造成負面影響，導致結構的不穩定、電容量的嚴重衰退和平均電壓的下降。

關鍵字

奈米 ； 鋰鎳鈷錳氧化物 ； 陰極材料 ； 層狀結構 ； 鋰離子電池

並列摘要

Layered structure LiNi1/3Co1/3Mn1/3O2 was successfully synthesized via the reverse microemulsion (RμE) route. Well crystallized and nanosized (about 45 nm) powders were obtained after calcining at 800oC for 3 h. The results of Rietveld refinement and XAS shows the yield products had high degree of cationic ordering. At the voltage range of 2.5 V to 4.5 V, LiNi1/3Co1/3Mn1/3O2 can deliver 187.2 mAh/g at room temperature and 195.5 mAh/g at 55oC, respectively. The prepared powers had low irreversible capacity (< 6 %) and good capacity retention. Nanosized LiNi1/3Co1/3Mn1/3O2 exhibited better kinetic performance than solid-state derived powders, which was micron order size. Once the upper cut-off voltage was 4.6 V, the capacity faded rapidly compared to other upper voltage limitations, which would be related to the redox reaction of cobalt ions. The charge transfer resistance at 4.59 V was larger than other potential stages, which may result in incomplete charge compensation for cobalt ions.

Layered structure LiNi1/3Co1/3Mn1/3-yAlyO2 (0 ≦ y ≦ 1/3) was synthesized via the sol-gel method. Their electrochemical behaviors, while cobalt ions involved in the redox reaction completely, were investigated. XANES confirms that the valence of Co was 3+ and that of Ni was between 2+ to 3+ in LiNi1/3Co1/3Mn1/3-yAlyO2. The amounts of lithium ions that can be deintercalated were limited with aluminum concentration. However the extracting fraction of lithium ions was improved with aluminum content. The electrochemical inactivity of aluminum ions exhibited obviously until y over a specific range. That influenced the kinetic performance and the charge
compensation of cobalt ions so that leaded to unstable structure, rapid capacity fading, and low average voltage compared to undoped LiNi1/3Co1/3Mn1/3O2.

並列關鍵字

Lithium-ion batteries ； Nanosized ； Cathode materials ； Layered structure ； LiNi1/3Co1/3Mn1/3O2

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