Cu掺杂P2型Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)钠离子电池正极材料的制备与性能

Synthesis and Performance of Cu Doping P2-Type Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)Used as Cathode Material for Sodium Ion Batteries

通过溶胶-凝胶法制备了一系列形貌规则、表面光滑的Cu掺杂层状P2型Na_(0.67)Ni_(0.33-x)Cu_(x)Mn_(0.67)O_(2)(x=0、0.05、0.10、0.15、0.20、0.25)。采用SEM、XRD、EDS、XPS对材料进行了形貌、结构和成分表征。将材料用作钠离子电池正极材料,采用循环伏安法、恒流充放电法研究了其电化学性能,获得了最佳掺杂比例。研究发现,掺杂未改变材料的层状结构和形貌,通过Cu掺杂引入了高电化学活性的Cu^(2+)作为取代基,增加材料的表面活性储钠位点,材料表现出良好的循环稳定性和倍率性能。在2.0~4.3 V的电压范围和0.1 C的倍率下,Cu掺杂比例x=0.15时Na_(0.67)Ni_(0.18)Cu_(0.15)Mn_(0.67)O_(2)的初始放电比容量为126.74 mAh/g,100次循环后容量保持率为79.10%,与未掺杂材料相比提高了50.92%。材料电化学性能的增强可归因于Cu^(2+)插入过渡金属层,由于Cu^(2+)(0.73A)的半径大于Ni^(2+)(0.69A),过渡金属层间距扩大,为Na+扩散提供了通道,进而提高了Na+扩散速率。当充电到高压时可抑制Na+脱/嵌过程中Na^(+)空位的产生,从而稳定材料的晶体结构并抑制材料发生P2-O2相变,提高了材料的循环稳定性。

A series of Cu-doped layered P2-type Na_(0.67)Ni_(0.33-x)Cu_(x)Mn_(0.67)O_(2)(x=0,0.05,0.10,0.15,0.20,0.25)with regular morphology and smooth surface were synthisized by sol-gel method.The morphology,structure and composition of those materials were characterized using SEM,XRD,EDS and XPS technologies,and their electrochemical properties were investigated by cyclic voltammetry and constant current charge-discharge methods through using them as cathode materials for sodium ion batteries.The optimum doping ratio was obtained.It is found that doping did not change the layered structure and morphology of the materials.Those materials exhibit good cycling stability and multiplicative performance due to the introduction of highly electrochemically active Cu^(2+)as a substituent and the increase of the surface active sodium storage sites.In the voltage range of 2.0 V to 4.3 V and a multiplicity of 0.1 C,the initial discharge specific capacity of Na_(0.67)Ni_(0.18)Cu_(0.15)Mn_(0.67)O_(2)(with Cu doped ratio of 0.15)has an initial discharge specific capacity of 126.74 mAh/g and a capacity retention rate of 79.10%after 100 cycles,which is 50.92%higher than that of the undoped material.The enhanced electrochemical properties of the material are attributed to the insertion of Cu^(2+)into the transition metal layer,and the radius of Cu^(2+)(0.73A)is larger than that of Ni^(2+)(0.69A),which widens the transition metal layer spacing and provides channels for Na+diffusion,and in turn increases the Na^(+) diffusion rate.When charged to high voltage,the Na+vacancy generation during Na^(+) de/embedding process is inhibited,thus the crystal structure of the material is stabilized,the P2-O2 phase transition is suppressed,and the cycling stability is improved.