石墨/LiCoO_2电池充放电过程电极活性材料结构演变研究

利用X射线衍射分析(XRD)详细地研究了石墨/LiCoO2体系18650型锂离子电池充放电过程中正负极活性材料的晶体结构和微结构的变化.结果发现,在电池充电过程中,锂嵌入石墨层中,优先进入碳原子六方网格面间的间隙位置,导致石墨的点阵参数a和c,以及微应变ε增加和堆垛无序度P的变化,电池充电至20%后负极中形成Li-C化合物;电池充电时,正极LiCoO2中处于(000)位的Li原子优先脱离晶体点阵,随着正极材料脱锂量的增大,其晶格参数a减小,c增大,微应变ε也随之增加.LiCoO2在整个充电和放电过程中均未发生相变.最后,讨论了锂离子电池的导电机制.发现,充电时,锂离子的迁移从负极-电解液界面开始;放电时,其迁移从正极-电解液界面开始;在充放电过程中,正负极活性材料的嵌脱锂都有一个从活性材料颗粒表面到内层的过程.电池的充放电过程不完全可逆.

Research on Structure Variation of Electrode Active Material during Charge-discharge for Graphite/LiCoO2 Battery

The variations of structure and microstructure of electrode materials in a graphite/LiCoO2 batteryduring charge-discharge process have been studied by X-ray diffraction (XRD).It is revealed that,in thecharge process,as intercalating into 2H-graphite,Li atoms preferentially occupy interstitial sites between Catom hexagonal net planes,which leads to increase of the lattice parameter a,c and micro-strain ～ andchange of stacking disorder P of 2H-graphite.When the battery is 20% charged,Li-C compounds areformed in the anode.Meanwhile,as for the cathode,in the charge process Li atoms occupying (000) sitesmay preferentially de-intercalate from LiCoO2 crystal lattice.With increase of the amount of Lide-intercalating,the lattice parameter,a and c,decreases and increases respectively,and its micro-strain eincreases.During the whole process of charge and discharge,no phase transformation happens to LiCoO2.Finally,the conductive mechanism of Li-ion battery has been discussed.The main points are as follows: thetransference of Li-ion starts from the anode-electrolyte interface in the charge process and reversely from thecathode-electrolyte interface in the discharge process.The intercalation and de-intercalation of Li into andfrom cathode and anode all go through a process from the surface to the inside of the particles.The chargeand discharge processes of Li-ion battery are not fully reversible.