Resolving Kinetic Limitations of Battery Materials from First Principles

电动汽车市场的扩大需要低成本、快速充电的锂离子电池。材料创新是满足日益增长的能源存储需求的关键。开发更好的电池材料有两个挑战：锂离子太小而看不见，并且它们在运行中不断移动。从第一性原理出发的原子模拟使我们能够以高保真度“看到”材料内部的动力学过程。我的研究目标是提供这种原子水平动力学的图片，这是不容易获得的实验。最终，我们的目标是利用我们的计算洞察力来加速新型电池材料的设计和制造。我们将模拟锂离子与主体材料中构建块的重排耦合的运动。这将使我们涵盖材料的合成，降解和表征。合成条件决定了宿主结构，特别是缺陷类型和浓度。退化与不可逆的结构变化有关，这些变化通常是在缺陷周围开始的。模拟表征将我们的原子图像与宏观测量联系起来。短期内，我们将重点研究富镍层状阴极和lifepo4基橄榄石阴极。它们都是消除昂贵和有毒Co使用的有希望的候选者，但它们的潜力尚未得到充分实现。两种材料在一定阶段都存在Li扩散速率慢的问题，这限制了它们的使用容量和充电速率。利用第一性原理计算，我们将研究这种动力障碍的结构起源和循环过程中的恶化。有了基本的了解，我们就可以在计算机上检查掺杂元素和合成条件的影响。在整个研究过程中，我们将模拟的电化学曲线与现有的实验进行比较，以证实我们的发现或改进我们的模型。工程目标是优化其组成和生产条件，以加速Li的扩散，同时抑制降解。我们研究的直接影响是深入了解电池材料的动力学过程，这将有助于确定速率限制步骤并解决扩散率测量中的差异。最终，这些见解可能会带来更便宜、充电更快、使用寿命更长的新电池，从而减少我们对环境的影响。在更广泛的影响上，该计划开发的计算框架将有利于相关领域，如合金腐蚀和电化学CO2捕获，通过实现长时间尺度和高精度的动力学模拟。最重要的是，该计划将培养具有最先进的方法和批判性思维技能的下一代研究人员。

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.