Synthesis and electrochemical properties of xLiMn_(0.9)Fe_(0.1)PO_4·yLi_3V_2(PO_4)_3/C composite cathode materials for lithium-ion batteries

摘要

ThexLiMn_(0.9)Fe_(0.1)PO_4·yLi_3V_2(PO_4)_3/C (x:y=1:0,9:1 5:1,3:1,1:1 and 0:1) cathode materials are synthesized by a ball-milling and post-calcination method. XRD results reveal that the xLiMn_(0.9)Fe_(0.1)PO_(4-)·yLi_3V_2(PO_4)_3/C (x,y≠0) composites are composed of LiMn_(0.9)Fe_(0.1)PO_4 and Li_3V_2(PO_4)_3 phases, and no impurities are detected. In LiMn_(0.9)Fe_(0.1)PO_4-Li_3V_2(PO_4)_3 system, most of the manganese, iron and vanadium elements in the raw materials tend to form the two major phases, and only small amounts of V, Mn and Fe as dopants enter into the lattice of LiMn_(0.9)Fe_(0.1)PO_4 and Li_3V_2(PO_4)_3. Electrochemical tests show that the xLiMn_(0.9)Fe_(0.1)PO_4·yLi_3V_2(PO_4)_3/C (x,y≠0) composites exhibit much better performance than the single LiMn_(0.9)Fe_(0.1)PO_4/C. Among the samples, 5LiMn_(0.9)Fe_(0.1)PO_4·Li_3V_2(PO_4)_3/C shows the best electrochemical performance. The sample delivers the specific capacities of 158.1,140.7 and 100.2 mAh g~(-1) at 0.05,1 and 4 C rates in the potential range of 2.5-4.5 V, and exhibits very long and flat discharge plateau around 4.0 V up to 1 C rate. The sample also shows good cycling performance at various C-rates.