提升矽陽極鋰離子電池之循環穩定性之研究

Abstract

矽是近年來鋰離子電池中備受矚目的陽極材料，因為矽有很高的比電容量(4200mAhg-1)等優點，但其最大的缺點是在鋰離子嵌入材料後，體積會膨脹造成電容量快速地衰減。本篇研究以簡單的方法製備矽陽極並利用調整不同的實驗條件，像是不同黏著劑和不同體積的溶劑去得到最佳化條件，使其組裝成鋰離子電池後，循環壽命增加、庫倫效率提高。 本篇材料是以奈米矽(~100nm)作為活性物質、碳黑(Super P)為導電碳材，和Sodium carboxymethyl cellulose(Na-CMC)為黏著劑，並使用pH=3的緩衝溶液作為電極漿料混和之溶劑。另外，本研究利用奈米石墨烯板(Graphene Nanoplatelets，GnPs)取代原本的碳黑並在電解液中添加10 wt.%的Fluoroethylene carbonate(FEC)和2 wt.%的Vinylene carbonate(VC)，以增加矽陽極的導電性及循環穩定性並減少不可逆電容量。最後，本研究以電流密度為1000mAg-1進行充放電程序，並將電容量限制在1500 mAhg-1可穩定維持175圈，甚至到200圈其電容量仍約有1200 mAhg-1。為了要評估循環的效率跟電化學性質，電池也以電流密度為200mAg-1進行測試。Silicon as anode for Lithium ion batteries (LIB) has attracted much attention due to its high capacity (4200 mAh g-1). However, the worst disadvantage is large volume expansion during lithiation resulting in fast fading of the capacity of silicon. In this study, silicon anodic electrodes in have been successfully prepared and the performance of the LIB also has been optimized via tuning different experimental parameters such as different binders and different volume of solvent. The fabrication of silicon anodic electrode slurry were based on using nano-silicon (100nm), carbon black (Super P), sodium carboxymethyl cellulose (Na-CMC) and a pH=3 buffer solution as active materials, conductive carbon, binder and solvent, respectively. In addition, we also utilized graphene nanoplatelets(GnPs) to replace carbon black and added 10wt. % Fluoroethylene carbonate(FEC) and 2wt. % Vinylene carbonate (VC) into liquid electrolyte for improving the conductivity and stability of silicon anodic electrode, thus reducing the irreversible capacity of cycles. Finally, the cycle stability of Si-LIB were improve to 175 cycles with a limited discharge capacity of 1500 mAhg-1 at a rate of 1000mAg-1 both in discharge and charge process, respectively. In order to evaluate the influence of the cycling rate on electrochemical properties, cells were also cycled by 200 mAg-1.