Abstract
Increasing the overall efficiency of Li-ion batteries through control of the organization and spatial arrangement of component materials is a promising route for continued improvements in energy and power density. This approach explores particle morphology, electrode thickness, additive content, particle packing and tortuosity, and interfacial connectivity. Particle, electrode, and interface scale phenomena of Li-ion batteries were explored in various Li-ion systems.
MnCO3 coprecipitation was used as a platform to create shape controlled monodisperse LiMn2O4 active material. Particle size distributions are among the most monodisperse demonstrated in the literature, and the shape was shown to be independently tunable for large particles. The transition at higher reagent concentrations from rhombohedral crystals to cubes, rough spheres, and progressively smaller, smoother spheres was shown in great visual detail. Unlike similar coprecipitation systems, it was determined that interparticle mass transfers were not significant in affecting particle morphology, and that particle size and shape was controlled by the initial nucleation and growth process.
The interfacial reactivity during heat treatment of two promising materials for all-solid-state batteries, LiMn1.5Ni0.5O4 (LMNO) active material and Li1.4Al0.4Ge1.6(PO4)3 (LAGP) solid electrolyte, was studied through X-ray diffraction and SEM/EDS. Two products were identified – Li-ion active material LiMnPO4 (LMP) and GeO2. LMP was shown to form a continuous interfacial phase at the interface, showing some promise towards generating a Li+ conductive connection between LMNO and LAGP. The reaction as-used was not able to create a high-performance connection between electrode and electrolyte, however, likely due to disconnections in the form of void spaces and GeO2 phases formed near the interface.
Highly thick (>500 μm) and dense (>62 % active) sintered electrodes which replace inactive additives with high temperature processing to form electronically conductive and mechanically robust interparticle bonds were investigated. Novel Li4Ti5O12/LiCoO2 full cell arrangements with high areal capacities were assembled and electrochemically characterized. The full cells were observed not to have the capacity fade issues seen in sintered electrode half cells. The full cells also have very good areal rate performance and capacities. A 2032 coin cell prototype using super thick electrodes with combined thickness 2.90 mm was shown to outperform commercial rechargeable 2032 cells in terms of energy and power.
