Wang Yanzhi, Tang Jiantao
Hebei Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University Qinhuangdao Hebei 066004 China
State Key Laboratory of Metastable Material Science and Technology, Yanshan University Qinhuangdao 066004 China.
RSC Adv. 2018 Jul 3;8(43):24143-24153. doi: 10.1039/c8ra04210a. eCollection 2018 Jul 2.
To improve the cycling stability and dynamic properties of layered oxide cathodes for sodium-ion batteries, surface modified P2-NaCoMnO with different levels of CeO was successfully synthesized by the solid-state method. X-ray photoelectron spectra, X-ray diffraction and Raman spectra show that the P2-structure and the oxidation state of cobalt and manganese of the pristine oxide are not affected by CeO surface modification, and a small amount of Ce ions have been reduced to Ce ions, and a few Ce ions have entered the crystal lattice of the P2-oxide surface during modification with CeO. In a voltage range of 2.0-4.0 V at a current density of 20 mA g, 2.00 wt% CeO-modified NaCoMnO delivers a maximum discharge capacity of 135.93 mA h g, and the capacity retentions are 91.96% and 83.38% after 50 and 100 cycles, respectively. However, the pristine oxide presents a low discharge capacity of 116.14 mA h g, and very low retentions of 39.83% and 25.96% after 50 and 100 cycles, respectively. It is suggested that the CeO modification enhances not only the maximum discharge capacity, but also the electric conductivity and the sodium ion diffusivity, resulting in a significant enhancement of the cycling stability and the kinetic characteristics of the P2-type oxide cathode.
为了提高钠离子电池层状氧化物阴极的循环稳定性和动力学性能，采用固态法成功合成了不同CeO含量的表面改性P2-NaCoMnO。X射线光电子能谱、X射线衍射和拉曼光谱表明，原始氧化物的P2结构以及钴和锰的氧化态不受CeO表面改性的影响，少量Ce离子被还原为Ce离子，并且在CeO改性过程中有少量Ce离子进入了P2-氧化物表面的晶格。在20 mA g的电流密度下，在2.0-4.0 V的电压范围内，2.00 wt% CeO改性的NaCoMnO的最大放电容量为135.93 mA h g，在50次和100次循环后容量保持率分别为91.96%和83.38%。然而，原始氧化物的放电容量较低，为116.14 mA h g，在50次和100次循环后的容量保持率分别极低，为39.83%和25.96%。结果表明，CeO改性不仅提高了最大放电容量，还提高了电导率和钠离子扩散率，从而显著提高了P2型氧化物阴极的循环稳定性和动力学特性。
