Resolving Kinetic Limitations of Battery Materials from First Principles

The expansion of electric vehicle (EV) market calls for low-cost and fast-charging Li-ion batteries. Materials innovation is the key to meet the ever-growing energy storage need. There are two challenges in developing better battery materials: Li ions are too small to be seen, and they are constantly moving under operation. Atomistic simulations from first principles empower us "seeing" the kinetic processes inside materials with high fidelity. The goal of my research is to provide pictures of such atomistic level kinetics, which are not easy to obtain experimentally. Ultimately, we aim to use our computational insights to accelerate the design and manufacturing of novel battery materials. We will simulate the motion of Li ions coupled with the rearrangement of building blocks in the host material. This will allow us cover materials synthesis, degradation, and characterization. Synthesis conditions determine the host structure, particularly the defect types and concentrations. Degradation is related to irreversible structure changes that often initiate around defects. Simulated characterizations connect our atomistic pictures to macroscopic measurements. In the short term, we will focus on the Ni-rich layered and the LiFePO4-based olivine cathodes. They are both promising candidates to eliminate the use of expensive and toxic Co, but their potentials have not yet been fully realized. Both materials suffer from slow Li diffusion rate at certain stage, which limits their usable capacities and charging rates. Using first-principles calculations, we will investigate the structural origin of such kinetic hindrance and the deterioration over cycling. With a fundamental understanding obtained, we can then examine the effects of doping elements and synthesis conditions on a computer. Throughout the research process we will compare the simulated electrochemical curves with existing experiments to either confirm our finding or improve our model. The engineering goal is to optimize the compositions as well as the producing conditions to accelerate Li diffusion while inhibiting degradation. The immediate impact of our research is to bring in-depth knowledge of kinetic processes in battery materials, which will help identify rate-limiting steps and resolve discrepancies in diffusivity measurements. Eventually, these insights could lead to new batteries that are cheap, charge faster and last longer, which reduce our environmental footprints. On the broader impact, the computational framework developed in this program will be beneficial to related fields, such as alloy corrosion and electrochemical CO2 capture, by enabling long-timescale and high-accuracy kinetic simulations. Most importantly, this program will prepare the next-generation researchers with state-of-art methods and critical thinking skills.