充放電電壓區間與熱處理對銅摻雜氧化錫奈米晶於鋰離子電池應用之影響

The Effects of Cutoff Voltage and Heat Treatment on the Behavior of a Nanocrystalline Cu-Doped Tin Oxide Applied to a Li-Ion Battery

以電化學沈積法在硝酸溶液中，銅摻雜氧化錫（Cu-doped tin oxide）奈米晶粒（5nm）鍍膜已成功被沈積於銅基板上。充放電電壓範圍與熱處理條件對其電化學性質之影響在本文中將進行深入探討。在長時間測試中，在充電過程於高電壓區間發生之Li2O 分解與在低電壓區間（0-0.3V vs. Li/Li+）發生之電解質消耗均會降低銅摻雜氧化錫奈米晶粒之電化學性質。在放電過程中銅摻雜氧化錫轉變為金屬錫與銅所造成的晶粒細化，使得金屬粒子的尺寸大小維持在大約3nm 左右。此一晶粒細化的過程避免了由於錫粒子晶粒成長所造成的電容量下降。與初鍍膜相比，經過400°C 熱處理的薄膜，由於在表面所吸附的OH 鍵與H2O 分子較少，使得在第一次放電過程中產生較少電子導電性差的Li2O，進而提升了其循環性。在1.5V-0.3V 的充放電電壓範圍，由於Li2O 的反應性及Li2O 與活性粒子間的良好附著性，而可以同時得到優異的循環性與高的電容量。 A nanocrystalline Cu-doped tin oxide (5 nm) coating was obtained by electrodeposition in a nitrate solution with Cu as the substrate. The effects of the cutoff voltage range and heat treatment on the electrochemical behaviors of an electrodeposited SnO2 coating were examined. In a long-term test, both the decomposition of Li2O during the charging stage in the high-voltage range and the consumption of the electrolyte in the low-voltage range (0 – 0.3 V vs. Li/Li+) damaged the electrochemical behavior of the Cu-doped tin oxide. The grain refinement during the discharging stage, caused by the transformation from Cu-doped SnO2 to metallic Sn and Cu, kept the grain size of the metallic particles at around 3 nm. This refinement avoided the capacity fading resulting from the grain growth of tin particles. Moreover, the heat treatment at 400o C enhanced the cyclability, due to the elimination of an OH bond and adsorbed H2O molecules, where less Li2O formed during the first discharging stage reduced the electric resistivity compared with the as-deposited coating. In the case of 1.5 V - 0.3 V, both a high capacity and good cycling were obtained due to the capacity contribution from the reaction of Li2O and good adhesion between the active particles and the Li2O matrix.