氟掺杂对LiMn_(0.8)Fe_(0.2)PO_(4)/C正极材料电化学性能的影响

Effects of fluorine doping on electrochemical behavior of LiMn_(0.8)Fe_(0.2)PO_(4)/C cathode materials

随着新能源汽车和锂离子电池的普及和推广,磷酸锰铁锂材料作为锂离子电池正极材料,其电化学性能亟待进一步优化。在诸多磷酸锰铁锂改性手段中,阴离子位取代的研究较少。LiF作为掺杂剂,通过F-取代PO_(4)^(3-)部分氧位的改性方法可提高磷酸锰铁锂的电化学性能。以Li_(2)CO_(3)、LiF、MnCO_(3)、FeC_(2)O_(4)·2H_(2)O、NH_(4)H_(2)PO_(4)和蔗糖为原料,通过高温固相法制备LiMn_(0.8)Fe_(0.2)PO_(4)−X_(F2)X/C(X=0.003、0.005、0.01、0.02)材料,并研究了不同氟掺杂量对LiMn_(0.8)Fe_(0.2)PO_(4)/C正极材料电化学性能的影响。结果表明,氟的掺入仅对LiMn_(0.8)Fe_(0.2)PO_(4)/C的晶格参数有轻微的改变,而对粒径影响不大;在电化学方面,氟掺杂使LiMn_(0.8)Fe_(0.2)PO_(4)/C具有良好的可逆容量和倍率性能,LiMn_(0.8)Fe_(0.2)PO_(3.99)F_(0.02)/C表现出最高的初始容量和最佳的倍率性能,0.1C和5C倍率下的放电比容量分别为155.1 mA·h/g和128.6 mA·h/g。相较于未掺杂的LiMnFePO_(4),LiMn_(0.8)Fe_(0.2)PO_(3.99)F_(0.02)/C在1C下循环500次后容量保持率从73.3%提高到96.1%。

With the popularization and promotion of new energy vehicles and lithium-ion batteries,the electrochemical performance of lithium manganese iron phosphate as cathode material for lithium-ion batteries needs to be further optimized.Among the modification methods of lithium ferromanganese phosphate,there are few studies on anion substitution.By the modification method of F^(-)replacing PO_(4)^(3-)partial oxygen site,LiF was used as a dopant to improve the electrochemical performance of lithium manganese iron phosphate.LiMn_(0.8)Fe_(0.2)PO_(4)−X_(F2)X/C(X=0.003,0.005,0.01,0.02)materials were prepared by high temperature solid state method using Li_(2)CO_(3),LiF,MnCO_(3),FeC_(2)O_(4)·2H_(2)O,NH_(4)H_(2)PO_(4)and sucrose as raw materials,and the effects of different fluorine doping contents on the electrochemical properties of LiMn_(0.8)Fe_(0.2)PO_(4)/C cathode materials were studied.The analyses demonstrated that fluorine could be incorporated into LiMn_(0.8)Fe_(0.2)PO_(4)/C without altering the olivinestructure,but slightly changing the lattice parameters and having little effect on the particle sizes.The results of electrochemical measurement showed that fluorine doping in LiMn_(0.8)Fe_(0.2)PO_(4)/C resulted in good reversible capacity and rate capability.LiMn_(0.8)Fe_(0.2)PO_(3.99)F_(0.02)/C exhibited highest initial capacity and best rate performance.Its discharge capacities at 0.1C and 5C rates were 155.1 mA·h/g and 128.6 mA·h/g,respectively.After 500 cycles at 1C,the capacity retention was increased from 73.3%to 96.1%compared with the unmodified materials.