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標題: Preparation of α-Fe2O3 on stainless steel as anodes for Li-ion thin film battery by electrochemical method
作者: 董仲霖
Don, Zhong-Lin
關鍵字: Electrolytic deposition;電化學沉積;α-Fe2O3;thin film lithium ion batteries;氧化鐵;薄膜鋰離子電池
出版社: 材料科學與工程學系所
Electrolytic α-Fe2O3 thin film on 304 stainless steel was carried out in aqueous solution for anodes in thin film lithium ion batteries. Through polarization tests, Cathodic reaction in aqueous solution were verified into 3 regions, including:
(1). O2 + 4H+ + 4e- → 2H2O (0.12V to -0.4V)
(2). 2H+ + 2e- → H2 (-0.4V to 0.88V)
(3). 2H+ + 2e- → H2 and/or Fe(OH)2+ + H2O + 2e- → FeOOH + H2 (-0.88V to -2.0V)
The porous as-deposited film was α-FeOOH, and condensed into uniform α-Fe2O3 at 250oC revealing thickness 10μm and particle size 10 nm. Cyclic voltammetry (CV) measurements showed oxidation peaks at 1.0 and 1.8 V, and reduction peaks at 1.2 and 0.63 V (Li/Li+). The first voltage of the discharge plateau was lowered and with increasing current density, accompanied with the coarsening of nano-sized particles and the reduced capacity. The coarsening effects were also found with increasing cycle number. It was suggested that the diffusion flux of Li+ in and out from α-Fe2O3 dominated the electrochemical reaction rate. The coarsening of α-Fe2O3 particles elongated the diffusion length of Li+, resulting in the capacity decay.

(1). O2 + 4H+ + 4e- → 2H2O (0.12 to -0.4 V)
(2). 2H+ + 2e- → H2 (-0.4 to 0.88 V)
(3). 2H+ + 2e- → H2 and/or Fe(OH)2+ + H2O + 2e- → FeOOH + H2 (-0.88 to -2.0 V)
初鍍膜成分為α-FeOOH且表面含有微孔洞,在250oC 熱處理後縮合形成厚度為10μm,晶粒約10nm的α-Fe2O3 均勻薄膜。半電池經循環伏安(CV)測試,氧化電位為1.0與1.8V,還原電位為1.2與0.63V(Li/Li+)。隨著衝放電電流密度的提高,放電平台相對降低且伴隨著晶粒粗化及電容量的下降,隨著衝放電次數增加也有晶粒粗化現象產生。顯然鋰離子在α-Fe2O3的嵌入與嵌出之擴散速率決定了反應速率,α-Fe2O3晶粒的粗化現象讓鋰離子的擴散路徑增長,導致電容量衰退。
Appears in Collections:材料科學與工程學系

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