NaH_(2)PO_(2)改性Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2)富锂正极材料的电化学性能

Electrochemical Performance of Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2) Cathode Materials Modified by NaH_(2)PO_(2)

采用不同物质的量的次亚磷酸钠对富锂正极材料进行改性处理,结果表明:采用4%(质量分数)的次亚磷酸钠改性处理的富锂正极材料表现出优异的循环稳定性,在0.5 C经过150圈循环后仍有85.3%的容量保持率,以及较高的首次Coulombic效率。材料优异的电化学性能一方面归因于次亚磷酸钠热解产生的还原性磷化氢气体与富锂正极材料表面活性氧反应产生氧空位,能够有效降低材料在首次充电过程中的不可逆容量损失;另一方面这一改性措施可以同时实现Na^(+)掺杂,起到稳定晶格结构,抑制相转变的作用,并且能够增大晶胞间距,加快锂离子扩散,降低电化学阻抗。此外,次亚磷酸钠热解所形成的焦磷酸钠包覆层可以保护正极材料,减少过渡金属溶解,从而改善材料循环性能。

Different amounts of NaH_(2)PO_(2) were used to treat lithium-rich cathode materials.The results show that the material treated by 4%(in mass fraction)NaH_(2)PO_(2) exhibits an excellent cycle stability with 85.3% of capacity retention after 150 cycles at 0.5 C and a high Coulombic efficiency.The enhanced electrochemical performance is attributed to the two following aspects.One aspect is that NaH_(2)PO_(2) pyrolysis produces reducing PH_(3) gas,which reacts with the active oxygen in the surface layer of the lithium-rich cathode materials to yield oxygen vacancy,thus effectively reducing the irreversible capacity loss in the first charge process.Another is that NaH_(2)PO_(2) pyrolysis treatment induces Na^(+) doping,which can effectively stabilize the lattice structure and inhibit phase transition,and accelerate Li^(+) diffusion and reduce the electrochemical impedance.In addition,the formed Na_(4)P_(2)O_(7) coating can protect the electrode material and reduce the dissolution of the transition metal,thereby improving the cycle stability.