高电位LiNi0.5Mn1.5O4正极材料制备、电化学性能与结构相变

Preparation,electrochemical performance and phase transition of high voltage LiNi_(0.5)Mn_(1.5)O_4 cathode material

尖晶石LiNi_(0.5)Mn_(1.5)O_4因其可在4.7 V高电位下工作并有良好的循环特性,已成为最具潜力的高能量密度锂离子电池正极材料。本文首先采用喷雾干燥辅助烧结法制备了LiNi_(0.5)Mn_(1.5)O_4正极材料,考察了热处理条件对材料结构与性能的影响。用XRD、SEM和FT-IR等技术对所制备的LiNi_(0.5)Mn_(1.5)O_4材料的结构和表面形貌进行表征,利用原位XRD技术研究了LiNi_(0.5)Mn_(1.5)O_4正极材料在充放电过程中结构相变规律。结果表明,所制备的LiNi_(0.5)Mn_(1.5)O_4材料均具有Fd-3m空间群的立方相尖晶石型结构,并具有优异的电化学性能,其0.1 C时首次放电容量为132 mA·h/g,首轮库仑效率93.48%,高倍率下该材料的电化学性能优越。原位XRD测量结果分析表明,尖晶石型LiNi_(0.5)Mn_(1.5)O_4材料在充电过程中存在4个显著的相变过程,在嵌脱锂过程中,从四面体相向立方相结构相变过程是可逆的。

Because of its good electrochemical performance and high operating voltage around 4.7 V, LiNi0.5Mn1.5O4 spinel has become one of the most promising high voltage cathode materials for lithium ion batteries with high energy density. In this paper, we prepared LiNi0.5Mn1.5O4 cathode materials through spray drying assisted annealing process with different heat treating conditions, the effect of heat treatment conditions on the structure and electrochemical performances was investigated. The crystal structures of the prepared LiNi0.5Mn1.5O4 materials were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transformed infrared spectroscopy （FT-IR）. The in situ synchrotron X-ray diffraction technique was carried out to study the online phase transition of LiNi0.5Mn1.5O4 spinel during cycling. It has been found that the prepared LiNi0.5Mn1.5O4 powders show phase-pure cubic spinel of Fd-3m structure. Its electrochemical performances were tested at different charge/discharge rates between the potential limit of 3.5-5.0 V, and the initial discharge capacity of the LiNi0.5Mn1.5O4spinel attained at 132.0 mA.h.g1, and the columbic efficiency at first cycle is 93.48%, and the electrochemical performances of the prepared materials are excellent.From the in situ XRD patterns and charge-discharge profile, it can be found that four phase transitions existed for LiNi0.sMnLsO4 spinel during charge process, the phase transition from tetrahedral to cubic is reversible in the lithium insertion and extraction process.