球狀天然石墨的改質及其在鋰離子二次電池的應用研究

Abstract

本研究的目的主要在探討藉由碳材被覆(Carbon coating)的方式，來改善石墨粉的表面結構與特性，進而改善其作為鋰離子二次電池陽極材料的性能。本實驗所採用的石墨粉分別為球形石墨，藉由酚酫樹脂於高溫中裂解成非結晶碳，在石墨表面上形成碳層被覆，進而穩定石墨的層狀結構，於鋰離子二次電池充放電過程中，不僅具有高電容，當球形石墨酚酫樹脂含量高達45wt%時，電容量高達380 mA h /g ，而且兼具穩定性，增強了鋰離子電池的使用效能。 經過XRD、石墨化度、Raman、及SEM掃描式電子顯微鏡分析，發現球形石墨經過800°C及1100°C的高溫熱處理後，由於酚酫樹脂於高溫中發生裂解成碳，於石墨表面形成ㄧ非晶質碳，使得石墨化度降低，而且在顆粒與顆粒之間有凝聚的現象。球形石墨熱處理溫度提高至1100°C時其可逆電容量與穩定度，庫倫效率明顯優於熱處理800°C的電池特性。

The purpose of this research was to improve characters and surface structure of graphite by carbon coating process to enhance the performance of lithium ion secondary batteries anode materials. This study used graphite prepared by spherical graphite. With phenol resin pyrolysis at high temperature, amorphous carbon was coated on the graphite surface to increase the graphite layer stability. When the added phenol resin amounts approaches 45wt%, the electrochemical quality shows the higher reversible capacities up to 380mAh/g and higher stability after several cycles. This result enhances the performance of the lithium ion batteries. Phenol resin was pyrolysized to hard carbon by covering on the graphite surface after heat treatment at 800°Cand 1100°C. It induces the decreasing of graphite crystallization and the increasing of agglomeration phenomenon among the particles as analyzed by using XRD and SEM. When temperature is raised to 1100°C, it shows the better characters of reversible capacities, stability and columbic efficiency than that heated at 800°C.