Mg掺杂提升钠离子电池正极材料高电压循环性能

Magnesium doping improved characteristics of high voltage cycle of layered cathode of sodium ion battery

钠离子电池层状氧化物正极材料具有高容量、易合成等优势,表现出巨大的应用潜力.为了开发出高容量、长循环的正极材料,本文提出对NaNi_(0.4)Cu_(0.1)Mn_(0.4)T_(i0.1)O_(2)(NCMT)用Mg^(2+)部分取代Ni^(2+)的改性策略,设计并合成了高容量、长循环的NaNi_(0.35)Mg_(0.05)Cu_(0.1)Mn_(0.4)Ti_(0.1)O_(2)(NCMT-Mg)正极材料.该材料在2.4—4.3 V电压范围内,显示165 mAh·g^(-1)的高可逆比容量.在0.1 C的倍率下循环350周后,仍有111 mAh·g^(-1)的可逆比容量,容量保持率为67.3%,相较于未掺杂的原始样品提升了约13%.本文对其进行了系统表征并揭示了其高电压循环稳定的机理,为开发出高性能钠离子正极材料提供了重要参考.

Driven by global demand for new energy,Li-ion batteries(LIBs)have developed rapidly due to their competitive performance.Although LIBs show the advantages of high capacity and good cycling stability,their disadvantages such as uneven distribution of lithium resources are gradually exposed.Therefore,with abundant reserves,Na-ion batteries(NIB)have become one of the most promising solutions to make up for the deficiency of Li-ion battery.The NIBs layered oxide cathodes have the most potential applications of cathode material due to their high specific capacity(167 mAh·g^(-1)in 2.4-4.3 V)and simple synthesis method.However,improving the cycling stability of layered cathode materials is one of the keys to their large-scale industrialization.To develop high capacity and cycling stability cathode materials,the Mg^(2+)is substituted for Ni^(2+)in NaNi_(0.4)Cu_(0.1)Mn_(0.4)Ti_(0.1)O_(2)(NCMT),thereby obtaining a NaNi_(0.35)Mg_(0.05)Cu_(0.1)Mn_(0.4)Ti_(0.1)O_(2)(NCMT-Mg)cathode material.The NCMT-Mg has a high reversible specific capacity of 165 mAh·g^(-1)in a voltage window of 2.4-4.3 V.The reversible specific capacity of about 110 mAh·g^(-1)at 0.1 C after 350 cycles with a capacity retention of 67.3%is about 13%higher than the counterpart of NCMT.The irreversible reaction is suppressed from P’3 phase to X phase for NCMT.The ex-XRD spectrometers further prove that the NCMT-Mg shows a P3 and X mixed phase after being initially charged to 4.3 V,but the NCMT shows an X phase.The irreversible phase transition is suppressed to increase the cycling stability.The inactive Mg^(2+)replaces Ni^(2+),reducing the charge compensation and stabilizing the structure,the inactive Mg^(2+)can activate the charge compensation of Ni^(2+)/Cu^(2+).The electrochemical activity increases from 77%to 86%.The high capacity and excellent cycling stability prove that the NCMT-Mg structure remains intact after various current rates have been tested.The long cycling stability mechanism is further systematically studied by using various technologies.The present work will provide an important reference for developing high-performance Na-ion cathode materials.