Lithium diffusion in Li₄Ti₅O₁₂ at high temperatures

详细信息    查看全文

• 作者：M. Vijayakumar ; Sebastien Kerisit ; Kevin M. Rosso ; Sarah D. Burton ; Jesse A. Sears ; Zhenguo Yang ; Gordon L. Graff ; Jun Liu ; Jianzhi Hu
• 关键词：Lithium battery ; Anode materials ; 6Li NMR ; Molecular dynamics
• 刊名：Journal of Power Sources
• 出版年：2011
• 出版时间：15 February 2011
• 年：2011
• 卷：196
• 期：4
• 页码：2211-2220
• 全文大小：1175 K

文摘

Synthesis of the spinel lithium titanate Li₄Ti₅O₁₂ by an alkoxide-free sol–gel method is described. This method yields highly pure and crystalline Li₄Ti₅O₁₂ samples at relatively low temperature (850 °C) and via short thermal treatment (2 h). ⁶Li magic angle spinning nuclear magnetic resonance (MAS NMR) measurements on these samples were carried out at high magnetic field (21.1 T) and over a wide temperature range (295–680 K). The temperature dependence of the chemical shifts and integral intensities of the three ⁶Li resonances demonstrates the migration of lithium ions from the tetrahedral 8a to the octahedral 16c sites and the progressive phase transition from a spinel to a defective NaCl-type structure. This defective structure has an increased number of vacancies at the 8a site, which facilitate lithium diffusion through 16c → 8a → 16c pathways, hence providing an explanation for the reported increase in conductivity at high temperatures. Molecular dynamics simulations of the spinel oxides Li_4+xTi₅O₁₂, with 0 ≤ x ≤ 3, were also performed with a potential shell model in the temperature range 300–700 K. The simulations support the conclusions drawn from the NMR measurements and show a significant timescale separation between lithium diffusion through 8a and 16c sites and that out of the 16d sites.