Investigation of high-performance lithium-ion batteries based on highly conductive Li7La3Zr2O12 solid-state electrolyte and stable electrode-electrolyte interface

With the merits of high Li+ conductivity, wide potential window, and electrochemical stability against metallic lithium anode (the highest theoretical capacity: 3,860 mAh g−1), cubic phase garnet-type Li7La3Zr2O12 (LLZO) solid-state electrolyte has attracted much attention for developing solid-state batteries with increased safety, higher energy density, and longer lifespan. Besides, the solid-state or liquid electrolyte/electrode interface stability and low resistance are important to their optimized electrochemical performance of lithium-ion batteries. The goal of this dissertation is to develop high-performance lithium-ion batteries based on LLZO solid-state electrolyte and stable/low resistance electrode-electrolyte interface via (1) low-temperature synthesis/densification of Al/Bi-doped cubic LLZO electrolytes, (2) surface modification of LiNi1/3Co1/3Mn1/3O2 cathode particles, (3) composite polymer electrolytes, and (4) application of plastic-crystal interfacial modification.Chapter 3 explores a low-temperature synthesis strategy to obtain cubic LLZO powders via a combination of sol-gel method and ball milling induced tetragonal to cubic phase transition, which is ~200 °C lower than the thermally induced phase transition temperature. Chapter 4 investigates the role of a facial B2O3 surface modification of LiNi1/3Co1/3Mn1/3O2 cathode particles to achieve a stable cathode-electrolyte interface, which enables improved high-rate discharge performance and enhanced cycling stability of the batteries. Chapter 5 reveals the effects of LLZO ceramic filler distribution and doping elements (Al and Bi) on the ambient-temperature ionic conductivity, Li+ transference number, electrochemical stability window, and ability to suppress lithium dendrite growth of poly(vinylidene fluoride) based composite polymer electrolytes, as well as solid-state battery performance based on these composite polymer electrolytes. In Chapter 6, cubic Bi-doped LLZO ceramic pellets with a high relative density (>90%) and ionic conductivity (~1.32×10^(-4) S cm-1 at 20 °C) were achieved with a sintering temperature as low as 900 °C. A succinonitrile-based plastic-crystal interlayer at the Li/LLZO interface was demonstrated to be very effective to reduce interfacial resistance and enable stable cycling of a Li/LLZO/Li symmetric cell. With the help of the plastic-crystal interlayer and a composite cathode, a Li/LLZO/LiCoO2 all-solid-state battery was fabricated, which displayed a stable cycling at 0.1C for 40 times at 20 °C with a discharge capacity of ~115 mAh g-1 and a Coulombic efficiency of ~99%.