钛酸锂负极的相分离机制

尖晶石钛酸锂(Li₄Ti₅O₁₂)作为锂离子电池负极材料具有长寿命、高稳定性的特点,是高功率锂离子电池的理想选择,对发展电动汽车以及智能电网有重要意义.结合球差校正透射电镜(STEM)、电子能量损失谱(EELS)和理论计算,在原子尺度观测到了尖晶石钛酸锂(Li₄Ti₅O₁₂)的结构,实现了对脱嵌锂过程的直接观测与表征.在锂化过程中,出现一个近似理想的异质界面(Li₄Ti₅O₁₂/Li₇Ti₅O₁₂),界面两侧Ti离子呈不同价态分布(Ti³⁺/Ti⁴⁺).而随着锂离子在材料中的嵌入和脱出,TiO₆八面体里面的Ti—O键会产生相应的收缩或拉伸("呼吸"模型),而这种键长的变化直接导致材料在不同区域的电子电导率产生质的变化(由绝缘体的Li₄Ti<...

Phase Separation in Li4Ti5O12 Anode for Li-Ion Batteries

Li₄Ti₅O₁₂ spinel has been regarded as one of the ideal anode materials for Li ion batteries and is a good candidate for developing high performance electric automobiles and smart grids for its characteristics of the long electrochemical cycle-life, high-structural stability and power density. Atomic-scale visualization of Li₄Ti₅O₁₂ spinel upon lithiation is realized using spherical aberration corrected transmission electron microscope (STEM), electron energy loss spectroscopy (EELS) and first-principles calculations. Upon lithiation, the Li₄Ti₅O₁₂ spinel transforms into the rock-salt Li₇Ti₅O₁₂ phase by developing an almost ideal hetero-interface and the Ti ions demonstrate different chemical states on the different sides of the interface. Further observation indicates that the elongation and shrinkage of Ti—O bonds in TiO₆ octahedra (breathing model) results in the fundamental changes of electronic conductivity in lithiated Li₄Ti₅O₁₂, where the insulating Li₄Ti₅O₁₂ is transformed into a quasi-conducting Li₇Ti₅O₁₂ phase. But these changes show limited influence on ionic conductivity. Using atomic-scale EELS analysis, a spontaneous oxidization process of Ti3+ to Ti4+ is revealed on the surface of Li₇Ti₅O₁₂ phase. This spontaneously surficial charge transfer reaction is revealed to be strongly related with the package swelling issue of Li₄Ti₅O₁₂ battery during cycling. Moreover, a three-phase separation, including the Li₄Ti₅O₁₂, Li₇Ti₅O₁₂ and Na₆LiTi₅O₁₂ phases, is found during Na insertion when Li₄Ti₅O₁₂ is employed as anode for sodium ion battery. All these important findings provide a rewarding avenue for the structural design and optimization of battery materials and lay a solid foundation for industrial application of Li₄Ti₅O₁₂ anode.