Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法，制备出了具有Ag/C 包覆层的层状富锂固溶体材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. 通过X 射线衍射（XRD）、场发射扫描电子显微镜（SEM）、透射电子显微镜（TEM）、恒流充放电、循环伏安（CV），电化学阻抗谱（EIS）和X 射线能量散射谱（EDS）方法，研究了Ag/C 包覆层对Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂电化学性能的影响. 结果表明，Ag/C 包覆层的厚度约为25 nm，Ag/C 包覆在保持了固溶体材料α-NaFeO₂ 六方层状晶体结构的前提下，显著地改善了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ 的电化学性能. 在2.0-4.8 V（vs Li/Li⁺）的电压范围内，首次放电（0.05C）容量由242.6 mAh·g^-1提高到272.4 mAh·g^-1，库仑效率由67.6%升高到77.4%；在0.2C倍率下，30 次循环后，Ag/C 包覆的电极材料容量为222.6 mAh·g^-1，比未包覆电极材料的容量高出14.45%；包覆后的电极材料在1C下的容量仍为0.05C下的81.3%. 循环伏安及电化学交流阻抗谱研究表明，Ag/C包覆层抑制了材料在充放电过程中氧的损失，有效降低了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂颗粒的界面膜电阻与电化学反应电阻.

Effects of Surface Modification with Ag/C on Electrochemical Properties of Li[Li0.2Mn0.54Ni0.13Co0.13]O2

A lithium-rich solid-solution layered cathode material, Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂, was synthesized using a fast co-precipitation method, and surface modified withAg/C via chemical deposition. The electrochemical properties, structures, and morphologies of the prepared samples were investigated using X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), galvanostatic charge-discharge cycling, cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and energy dispersive X-ray spectroscopy (EDS). The XRD results showed that the pristine and Ag/Ccoated cathode materials both have hexagonal α-NaFeO₂ layered structures with the R3m space group. Microscopic morphological observations and EDS elemental mapping showed that a uniform Ag/C coating layer of thickness 25 nm was deposited on the surfaces of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ particles. The Ag/C-coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ material gave an excellent electrochemical performance. The initial discharge capacity (0.05C) of the Ag/C- coated sample was 272.4 mAh ·g^-1, with an initial coulombic efficiency of 77.4%, corresponding to 242.6 mAh·g^-1 for the pristine sample, with an initial coulombic efficiency of 67.6%, in the potential range 2.0-4.8 V (vs Li/Li⁺). After 30 cycles (0.2C), the Ag/C-coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ retained a capacity of 222.6 mAh·g^-1, which was 14.45% higher than that of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. We also found that the Ag/C coating improved the rate capability of the solid-solution material Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. The capacity retention (1C) of the Ag/C-coated sample was 81.3%, compared with the capacity at 0.05C. CV and EIS results showed that the Ag/C coating layer suppressed the oxygen release in the initial charge progress and lowered the surface film resistance and electrochemical reaction resistance of the pristine sample.