The Spinels in Lithium-Ion Batteries

A battery is a phenomenal test vehicle to study interesting topics in Solid State Ionics, such as crystals’ point defects, materials interface stabilities and reaction kinetics, mixed ionic-electronic conduction behaviors and so forth. To explore these subjects, I synthesized a group of spinels and reviewed their performances in lithium-ion batteries. Both lab prepared samples and commercial powders suggested that, when using LiMn₂O₄as the battery cathodes, the loss of energy was associated with the level of oxygen deficiencies in their crystal structures. Meanwhile, for the first time, the manganese displacement and migration at high potentials were observed. Mechanical fractures of LiMn₂O₄-_dparticles caused poor charge transfers within electrodes, which downgraded cell power capabilities. However, when manganese is partially substituted by nickel, LiNi_0.5Mn_1.5O₄-_dshowed superior electrochemical performances in testing cells, which was attributed to the effect of cation disordering. A hidden charge transfer mechanism between the nickel and manganese was proposed. Based on that, I designed a new cycling protocol and all the cells were able to last over one thousand cycles without any capacity drop. The research also investigated a nanoscaled amorphous coating on LiNi_0.5Mn_1.5O₄-_d, which played as a kinetic barrier to negate surface side reactions in batteries. In the end, a new approach was attempted to synthesize high power Li (Li_1/3Ti_5/3) O₄anode powders. Although without any conductive coating on the titania particles, robust energy retentions under high current densities highlighted the role of electrodes structure design.