真空合成锂离子电池LiFePO_4/C正极材料及其电化学性能研究

Electrochemical Properties of LiFePO_4/C Cathode Materials Prepared under Vacuum Conditions

以氢氧化锂为锂源,在真空条件下合成了锂离子电池正极材料LiFePO4.采用X射线衍射(XRD)、扫描电镜(SEM)对样品进行表征,并对其进行电化学交流阻抗(EIS)、循环伏安(CV)和恒流充放电等电化学性能测试,并与以碳酸锂为锂源制得的材料进行比较.结果表明:两种锂源在真空条件下合成的LiFePO4均具有单一的橄榄石相,而以氢氧化锂为锂源所得的材料粒度更小且分布更均匀,比容量更高.此外,以氢氧化锂为锂源时,通过在原料预烧后的前驱体中引入碳源得到的LiFePO4/C复合正极材料在0.2 C和1.0 C时的首次放电容量分别为138.4 mAh/g和126.8mAh/g,循环30次后仍能分别释放出135.6 mAh/g和123.9 mAh/g的可逆容量.

LiFePO4 was prepared under vacuum conditions using LiOH as lithium sources. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to detect the phases presented in the composites and observe sample morphology. In addition, AC Electrochemical Impedance Spectroscopy （EIS）, cyclic voltammetry （CV）, along with constant current discharge/charge tests, were used to characterize the electrochemical properties of the composites. It was shown that samples prepared using both LiOH and Li2COa as lithium sources indicated a single olive crystal structures, but the LiFePO4 using the former lithium sources delivered higher discharge capacity with smaller particles and highly dispersion. Furthermore, LiFePO4/C could also be obtained using LiOH and adding carbon source after preheating treatment. The LiFePO4/C sample could deliver a discharge capacity of 138.4 and 126.8 mAh/g in the first cycle at 0.2 and 1.0C, respectively, and kept a reversible capacity of 135.6 and 123.9 mAh/g after 30 cycles.