石墨在碳酸酯基电解液中储钠活性很低,因此被认为不合适作为钠离子电池负极材料。而最近的研究表明,在以线性醚为溶剂的钠离子电解液中,石墨具有高的储钠容量和首圈库伦效率。因此,探索这种溶剂依赖型的石墨界面演绎过程具有重要的意义...石墨在碳酸酯基电解液中储钠活性很低,因此被认为不合适作为钠离子电池负极材料。而最近的研究表明,在以线性醚为溶剂的钠离子电解液中,石墨具有高的储钠容量和首圈库伦效率。因此,探索这种溶剂依赖型的石墨界面演绎过程具有重要的意义。本研究采用原位原子力显微镜(Atomic force microscopy,AFM)实时观测石墨在碳酸酯基和线性醚基电解液下的界面微观动态过程。结果表明:在线性醚溶剂下,石墨电极界面没有固体电解质界面膜(Solid electrolyte interphase,SEI)形成,且溶剂化钠离子可以在石墨层间进行可逆的插入和脱出,AFM结果从界面角度解释了其具有高初始库伦效率的内在原因。然而在碳酸酯溶剂中,可以观察到石墨电极表面出现明显的沉积物,对应SEI的生长;并且在充电过程中SEI逐渐减少,表明碳酸酯溶剂下形成的SEI不稳定,造成不可逆的容量损失和低库伦效率。此外,石墨表面未出现明显的台阶变化,反映了没有钠离子的脱嵌过程。上述研究结果为石墨负极界面反应动态过程提供了见解,从微观尺度揭示了溶剂依赖的石墨负极储钠行为及其界面反应机理,为高性能钠离子电池体系的设计与发展提供了理论依据。展开更多
Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- call...Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- cally reconstructed the three-dimensional microstructure of a graphite anode. The reconstructed anode is a composite of three clearly distinguished phases： pore （or electrolyte）, graphite, and solid additives, well representing the non- isotropic heterogeneous characteristic of real graphite anode. Characterization analysis of the reconstructed electrode gives information such as the connectivity of individual phase, the specific interracial area between solid and pore phase, and the pore size distribution. The effects of the ellipsoid size on the structural characteristics of graphite anode were particularly studied. As the size of the ellipsoidal particle slightly increases, the average pore diameter increases and as a result the specific interfacial area between the solid and pore phase in the reconstructed area decreases; compared with the equatorial radius, the polar radius of ellipsoidal graphite particles has more sig- nificant influence on the characteristics of electrode microstructure.展开更多
文摘石墨在碳酸酯基电解液中储钠活性很低,因此被认为不合适作为钠离子电池负极材料。而最近的研究表明,在以线性醚为溶剂的钠离子电解液中,石墨具有高的储钠容量和首圈库伦效率。因此,探索这种溶剂依赖型的石墨界面演绎过程具有重要的意义。本研究采用原位原子力显微镜(Atomic force microscopy,AFM)实时观测石墨在碳酸酯基和线性醚基电解液下的界面微观动态过程。结果表明:在线性醚溶剂下,石墨电极界面没有固体电解质界面膜(Solid electrolyte interphase,SEI)形成,且溶剂化钠离子可以在石墨层间进行可逆的插入和脱出,AFM结果从界面角度解释了其具有高初始库伦效率的内在原因。然而在碳酸酯溶剂中,可以观察到石墨电极表面出现明显的沉积物,对应SEI的生长;并且在充电过程中SEI逐渐减少,表明碳酸酯溶剂下形成的SEI不稳定,造成不可逆的容量损失和低库伦效率。此外,石墨表面未出现明显的台阶变化,反映了没有钠离子的脱嵌过程。上述研究结果为石墨负极界面反应动态过程提供了见解,从微观尺度揭示了溶剂依赖的石墨负极储钠行为及其界面反应机理,为高性能钠离子电池体系的设计与发展提供了理论依据。
基金supported by the Key Scientific Development Project of Guangdong Province(2015A030308019)the Guangzhou Scientific and Technological Development Plan(2014J4100217)the Hundred Talents Program of Chinese Academy of Sciences
文摘Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- cally reconstructed the three-dimensional microstructure of a graphite anode. The reconstructed anode is a composite of three clearly distinguished phases： pore （or electrolyte）, graphite, and solid additives, well representing the non- isotropic heterogeneous characteristic of real graphite anode. Characterization analysis of the reconstructed electrode gives information such as the connectivity of individual phase, the specific interracial area between solid and pore phase, and the pore size distribution. The effects of the ellipsoid size on the structural characteristics of graphite anode were particularly studied. As the size of the ellipsoidal particle slightly increases, the average pore diameter increases and as a result the specific interfacial area between the solid and pore phase in the reconstructed area decreases; compared with the equatorial radius, the polar radius of ellipsoidal graphite particles has more sig- nificant influence on the characteristics of electrode microstructure.
