铕掺杂改善锂离子电池正极材料LiFePO_(4)电化学性能研究

Study on electrochemical properties of europium⁃doped LiFePO_(4)cathode material for lithium⁃ion battery

橄榄石结构的LiFePO_(4)正极材料因其多重优势被广泛应用于新能源汽车和储能领域,但其较差的电导率和缓慢的锂离子扩散速率限制了其低温和倍率等性能。元素掺杂被认为是一种改善正极材料倍率、低温等性能的有效策略。采用固相法合成了稀土金属铕掺杂的Li Fe_(1-x)Eu_(x)PO_(4)/C正极材料,并研究了铕掺杂量对Li Fe PO_(4)形貌、结构和电化学性能的影响。结果表明,铕掺杂能够改善Li Fe PO_(4)/C的电化学性能,其中Li Fe_(0.97)Eu_(0.03)PO_(4)/C表现出最佳的倍率、低温和循环性能,其组成的纽扣电池在20C高倍率下放电比容量为95.1 m A·h/g(较Li Fe PO_(4)/C提升57.7%),在低温(-20℃、0.1C)下的放电比容量为81.5 m A·h/g(较Li Fe PO_(4)/C提升73.8%),1C下经200次循环后其容量保持率为96.43%(较Li Fe PO_(4)/C高出2.46%)。X射线衍射分析和扫描电镜分析结果表明,铕的掺入能增大Li Fe PO_(4)的晶胞体积,降低Li和O原子之间的结合能,从而提高锂离子的扩散速率。电化学交流阻抗测试结果表明,Li Fe_(0.97)Eu_(0.03)PO_(4)/C表现出最低的电荷转移电阻和最高的锂离子扩散系数,其锂离子扩散系数比未掺杂的Li Fe PO_(4)/C高出2个数量级,这解释了其出色的倍率、低温和循环性能。

The olivine LiFePO_(4)cathode material is widely used in the field of electric vehicles and energy storage due to its multiple advantages,however,its low temperature and rate performance are limited by poor electrical conductivity and slug‐gish lithium ions diffusion kinetics.Elemental doping is considered to be an effective strategy to improve the properties of cath‐ode materials such as multiplicity and low temperature performance.Here,rare earth metal europium‐doped LiFe1-xEuxPO_(4)/C cathode materials were synthesized by solid‐phase method,and the effects of europium doping on the morphology,structure,and electrochemical properties of LiFePO_(4)were investigated.The results showed that europium doping could improve the electrochemical properties of LiFePO_(4)/C.The LiFe_(0.97)Eu_(0.03)PO_(4)/C showed the best rate,low temperature and cycling perfor‐mance,with its discharge capacity of 95.1 mA·h/g at high rate of 20C(57.7%enhancement compared with that of LiFePO_(4)/C),discharge capacity of 81.5 mA·h/g(73.8%enhancement compared with that of LiFePO_(4)/C)at low temperature of-20℃,and capacity retention rate of 96.43%(26.2%enhancement compared with that of LiFePO_(4)/C)after 200 cycles at 1C.X-ray diffraction(XRD)and scanning electron microscopy(SEM)results showed that the europium doping could in‐crease the cell volume of LiFePO_(4)and decrease the binding energy between Li and O atoms,which could improve the diffu‐sion rate of lithium ions.Electrochemical alternating impedance(EIS)test results showed that LiFe_(0.97)Eu_(0.03)PO_(4)/C exhibited the lowest charge transfer resistance,and the highest lithium ion diffusion coefficient that was two orders of magnitude higher than that of the undoped LiFePO_(4)/C,which explained its excellent rate,low‐temperature and cycling performance.