Understanding the Role of NH4F and Al2O3 Surface Co-modification on Lithium-Excess Layered Oxide Li1.2Ni0.2Mn0.6O2

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• 作者：Haodong Liu ; Danna Qian ; Michael G. Verde ; Minghao Zhang ; Lo茂c Baggetto ; Ke An ; Yan Chen ; Kyler J. Carroll ; Derek Lau ; Miaofang Chi ; Gabriel M. Veith ; Ying Shirley Meng
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：September 2, 2015
• 年：2015
• 卷：7
• 期：34
• 页码：19189-19200
• 全文大小：813K
• ISSN：1944-8252

文摘

In this work we prepared Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) using a hydroxide co-precipitation method and investigated the effect of co-modification with NH₄F and Al₂O₃. After surface co-modification, the first cycle Coulombic efficiency of Li_1.2Ni_0.2Mn_0.6O₂ improved from 82.7% to 87.5%, and the reversible discharge capacity improved from 253 to 287 mAh g^鈥? at C/20. Moreover, the rate capability also increased significantly. A combination of neutron diffraction (ND), high-resolution transmission electron microscopy (HRTEM), aberration-corrected scanning transmission electron microscopy (a-STEM)/electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) revealed the changes of surface structure and chemistry after NH₄F and Al₂O₃ surface co-modification while the bulk properties showed relatively no changes. These complex changes on the material鈥檚 surface include the formation of an amorphous Al₂O₃ coating, the transformation of layered material to a spinel-like phase on the surface, the formation of nanoislands of active material, and the partial chemical reduction of surface Mn⁴⁺. Such enhanced discharge capacity of the modified material can be primarily assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material facilitated with preactivated Mn³⁺ on the surface, and stabilization of the Ni-redox pair. These insights will provide guidance for the surface modification in high-voltage-cathode battery materials of the future.