利用溶膠-凝膠法製作氧化鋁披覆於摻雜鎂之鋰鎳鈷錳氧材料以改善其高溫循環壽命

Abstract

在鋰離子電池發展中，鋰鎳鈷錳氧化物(LiNi0.5Co0.2Mn0.3O2)是近幾年來相當受矚目的正極材料。主要的原因是因為其能有效彌補傳統鋰鈷材料(LiCoO2)放電電容量較低的問題，同時也改善高鎳系材料(LiNiO2)熱穩定性不足的缺陷。然而，鋰鎳鈷錳氧化物因其仍富含較高的鎳含量，使得氧化物中三價的鎳容易還原成二價而與氧結合造成較高的不可逆電容量並使循環壽命降低。因此，希望藉由表面改質的方式，能夠有效改善上述提及的問題。此篇研究利用溶膠-凝膠法的表面改質方法，測試在不同金屬氧化物前驅物、不同披覆劑量、溶劑改變與低溫燒結條件以尋求非傳統形貌的金屬氧化物披覆，進而下提升其高溫循環壽命。而本篇研究所改質出的鋁氧化物披覆於参雜鎂之鋰鎳鈷錳氧化物在鋰離子半電池壽命高溫測試(55oC)，經過將近300圈的充放電後仍有113.6mAh/g的電容量(殘存電容量為73.1%)。 我們利用XRD、SEM、TEM、EDX、DSC 與AC impedance等分析輔助討論粉體表面改質與電化學電性測試的結果，希望能發展出一簡單、便宜並能有效改善循環壽命的改質方法。

In the development of lithium-ion batteries, LiNi0.5Co0.3Mn0.2O2 has been paid more attention for cathode materials. The high discharging capacity and thermal stability which compensate for the insufficient capacity of LiCoO2 and the drawback of Ni-rich cathode, respectively, are the leading reason. However, owing to the higher Ni content of LiNi0.5Co0.3Mn0.2O2, unstable Ni3+ ions were prior to reduce to Ni2+ on the cathode surface in the form of NiO and leads to higher irreversible capacity and poor cycle life. Therefore, we make efforts to solve these problems mentioned above by surface modification. This study, by sol-gel method of surface modification, was aimed to search for non-tradition metal oxide coating to improve cyclability at high temperature by testing different metal oxide precursors, coating amounts, solvents, and lower annealing condition. In this study, the lithium-ion half battery testing cyclability at 55oC for AlOx coating on Mg-doped LiNi0.5Co0.3Mn0.2O2 was kept to 300 cycles, with capacity of 113.6mAh/g in the capacity retention of 73.1%. By the analysis of XRD (X-ray diffraction)、SEM (Scanning electron microscope)、TEM (Transmission electron microscope)、EDX (Energy dispersive X-ray)、DSC (Differential scanning calorimetry) and AC impedance (Alternating current impedance) for surface modification of cathode and the result of cyclability, we look forward to set up a simple and low-cost modifying method improving cycle life.