Al离子掺杂及石墨烯包覆对Na_(3)V_(2)(PO_(4))_(2)F_(3)正极材料的影响

Al Ion Doping and Graphene Coating Effects on Na_(3)V_(2)(PO_(4))_(2)F_(3) Anode Material

采用一步水热法合成Na_(3)V_(2-x)Al_(x)(PO_(4))_(2)F_(3)(x=0、0.1、0.5、0.7)钠离子电池正极材料,并采用XRD、SEM、电池测试仪和电化学工作站对合成的材料进行表征、分析和测试。结果表明,Al离子掺杂降低Na_(3)V_(2)(PO_(4))_(2)F_(3)正极材料的能隙,提高了其电子电导率。当x=0.5时,正极材料循环至35周时的可逆比容量最高,容量保持率最低。根据所得结果选择性能最优的Na_(3)V_(1.5)Al_(0.5)(PO_(4))_(2)F_(3)正极材料进行了石墨烯包覆处理,并与未包覆的材料进行性能对比。石墨烯包覆前后样品循环至25周的可逆比容量分别为17.4 mAh·g^(-1)和47.7 mAh·g^(-1),容量保持率分别为59.6%和82.9%。石墨烯包覆后的Na_(3)V_(1.5)Al_(0.5)(PO_(4))_(2)F_(3),电荷转移电阻减小,晶体结构中钠离子传输速率提高,石墨烯包覆能有效提高Na_(3)V_(1.5)Al_(0.5)(PO_(4))_(2)F_(3)正极材料的电化学性能。

Na_(3)V_(2-x)Al_(x)(PO_(4))_(2)F_(3)(x=0、0.1、0.5、0.7)sodium ion anode material was synthesized by one-step hydrothermal method.XRD,SEM,battery tester and electrochemical workstations were used to characterize the synthezed materials.It is found that Al doping can reduce the energy gap and increase the electronic conductivity of Na_(3)V_(2)(PO_(4))_(2)F_(3).Moreover,when the value of x is equal to 0.5 and after 35 charge and discharge cycles,the reversible specific capacity of the formed anode materials possesses the largest value,but the capacity retention rate is the lowest comparing with that of other formed materials.Additionally,Na_(3)V_(1.5)Al_(0.5)(PO_(4))_(2)F_(3) was coated with graphene and the same properties were also characterized.The results show that after 25 charge and discharge cycles the reversible specific capacities of the bare and coated Na_(3)V_(1.5)Al_(0.5)(PO_(4))_(2)F_(3) were 17.4 mAh·g^(-1) and 47.7 mAh·g^(-1),and the capacity retention rates were 59.6%and 82.9%,respectively.Obviously,the graphene coating can effectively improve the electrochemical properties of the formed material.