两种碳源对橄榄石型正极材料LiFePO_4性能的影响

Effects of Different Carbon Sources on the Performance of Olivine LiFePO_4/C Cathode Material

采用固相反应法在惰性气体气氛下合成了橄榄石型LiFePO4及LiFePO4/C复合正极材料,采用XRD,SEM以及电化学测试等手段对材料进行了结构表征和性能测试。考察了蔗糖、石墨两种碳源对材料性能的影响。XRD结果表明,两种碳源的添加对LiFePO4的晶体结构没有明显的影响;SEM表明,掺杂后,样品的粒径变小;充放电测试表明,和未掺杂的LiFePO4相比掺杂石墨和掺杂蔗糖的LiFePO4具有更好的电化学性能,放电比容量分别为:138.85 mAh.g-1和126.2 mAh.g-1,高于纯的LiFePO4正极材料的容量90 mAh.g-1。经100次循环后,掺杂蔗糖、掺杂石墨及未掺杂的LiFePO4样品的容量衰减率分别为0.02%,1.2%和47%。

Olivine LiFePO4 and LiFePO4/C composite cathode materials were synthesized by a solid state method in an inert atmosphere. The crystal structure and the electrochemical performance were characterized by XRD, SEM and electrochemical performance testing. The effects of two different carbon sources, i. e. sucrose and graphite, on the performance of as-synthesized cathode materials were investigated. The results demonstrated that the composite material carbondoped by sucrose had the most excellent electrochemical performances. The addition of small amount of carbon had no obvious effect on the structure of lithium iron phosphate while the cathode material showed better electrochemical performance. The discharge capacities of the samples （LiFePO, carbon-doped by graphite and by sucrose） as a lithium secondary battery were 138.85 mAh·g^-1 and 126.2 mAh·g^-1 at 0. 1 C （corresponding to 17 mAh·g^-1） , larger than that of LiFePO4 （90 mAh·g^-1）. After 100 cycles, the capacity fade of LiFePO4, LiFePO4 carbon-doped by graphite and by sucrose was 47% , 1.2% and 0.02% , respectively.