Cathode Materials for Lithium-Ion Batteries

[[abstract]]本論文主要討論有兩種具有高能量密度的材料，這些材料有助於未來下一世代的電池系統，其中一項為富鋰且多錳的鎳鈷錳三元系統材料另一項為五氧化二釩系統。富鋰且多錳的鎳鈷錳三元系統正極組成為Li(Li0.08Ni0.34Co0.8Mn0.5)O2是由共沉法製成，經由XRD分析為單斜晶系C 2/m空間群經過電化學反應後相轉變為R -3m之結構，以ICP-OES做化學劑量的確認，電化學反應由循環伏安法以及充放電儀來確定電化學穩定性，電容量為205 mAh/g在電化學視窗為2.2到4.6V，無論是全電池或是鈕扣型電池都具有良好的穩定性在50次充放電後只有5%以下的電容量損失。另一項材料為五氧化二釩，選擇此材料是由於五氧化二釩具有不可逆向轉移的問題，在此使用兩種有機材料尿素以及三聚氰胺插入五氧化二釩結構層中以穩定材料，此材料在室溫中使用一步反應合成尿素/V2O5 奈米線以及 三聚氰胺/V2O5 奈米管，三聚氰胺/V2O5為三斜晶系P-1空間群。在實驗中三聚氰胺成功的穩定了材料，五氧化二釩與三聚氰胺以氫健健結成功的阻止再低電壓的結構相變，電容量為184 mAh/g在電化學視窗為1.9到3.4 V，此電容量非常的接近兩個鋰插層的五氧化二釩，此材料在100次充放電後還保有85%以上的電容量。[[abstract]]This work primarily focuses on two important high energy density materials that have potential to meet the demands of the next generation technologies in satiating the need for energy. One belonging to the family of Ni-Co-Mn with rich lithium and manganese and the other is vanadium pentoxide. A lithium- and manganese-rich Li-Ni-Co-Mn-O cathode material Li(Li0.08Ni0.34Co0.8Mn0.5)O2, a combination of traditional battery components with a unique stoichiometry is prepared via co-precipitation method. XRD studies show the material is a single phase with C 2/m space group that falls in the monoclinic crystal system which upon electrochemical activation, goes through an irreversible phase transformation to R -3m which is stable throughout the electrochemical reactions. ICP-OES confirms the right stoichiometry. Electrochemical analysis through cyclic voltammetry and charge/discharge studies revealed the stability of the material during electrochemical reactions is tremendous. The output capacity achievable was around 205 mAh/g in the voltage range 2.2 to 4.6 V both in coin cells and full cells as well and an excellent cyclability with less than 5 % decay in the capacity after 50 cycles of charge/discharge in the case of full cell. As an alternative to the conventional materials, V2O5 was selected and the main emphasis was on solving the irreversible phase transition problem. Two organic compounds, urea and melamine were introduced into the layers of V2O5 as structure stabilizing agents during the phase transitions. Room temperature one step synthesis route delivered Urea/V2O5 nanowires and melamine/V2O5 nanorods. The melamine/V2O5 revealed a self-assembled single phase hybrid with P-1 space group belonging to the triclinic crystal system. Melamine was successful in acting as a stabilizing agent, while urea failed in serving the purpose. The hydrogen bonds between the V2O5 layers and melamine molecules assisted in preventing the puckering problem during the discharge processes at lower voltage making the phase transition reversible. A substantial specific capacity of 184 mAh/g was possible at the voltage range 1.9 to 3.4 V, very close to the theoretical capacity with two moles of lithium insertion per molecule. It showed a considerable cyclability with the retention of more than 85 % of its initial capacity when the coin cell was run for 100 cycles.[[note]]博