Non-delaminated 2D MXene stacks modified Li surface: a reliable, scalable thin inter-layer-calated Li metal anode with improved cyclability and dendrite suppression

以负担得起的成本储存能源已成为能源部门面临的挑战性问题之一，对于从电动汽车到可再生能源的电网储存等广泛应用至关重要。电动汽车对高能量密度电池的需求迅速增长，要求科学家探索能够提供更高能量容量的新电极材料。为此，锂金属正在下一代锂离子电池中引起广泛关注。然而，不稳定和不可逆的锂电镀/剥离会导致电池寿命较短，并可能导致锂的枝晶生长，从而导致严重的安全问题。这一基础研究项目旨在开发一种由新型二维碳化物或氮化物纳米材料MXenes组成的混合电极，以构建复合锂金属阳极。涂覆的2D MXene层在层之间提供了大量的空隙，更好的导电性，并抑制了树枝晶的生长。这种材料设计方法也适用于制造电池阳极的大规模制造方法。如果成功，研制的锂金属电极可以应用于各种液体电解液和固态电池。该项目的实验设计、问题解决和性能分析将与面向科学、技术、工程和数学(STEM)领域的本科生的教育推广相结合，特别是在材料科学和工程的储能领域，通过一系列激动人心的研究经验和课程。像MXenes这样的二维纳米材料在锂电池中显示出巨大的前景，因为它在层之间高效而快速的离子传输，以及可用于改善离子吸附和更快的表面氧化还原反应的大表面积。MXenes中开放的离子传输通道缩短了离子扩散路径，实现了快速离子传输。此外，它们还可以作为功能衬底，为锂离子电池整合各种活性材料，提高电极的总容量，提高整体性能。本研究项目的技术目标是设计一种可扩展的二维MXenes，如Ti3C2Tx堆叠层间夹层薄层Li金属杂化负极，在锂离子电池的长循环中表现出高度可逆的电镀/剥离和低过电位。具有高机械灵活性的多层MXene堆栈的大表面积确保了在电镀和剥离时高容量和可靠的锂成核/生长。高度可逆的锂通过受限的2D构型，通过形成薄的固体电解质界面层(SEI)来减少死锂和电解液消耗。用原位观察和模拟的方法研究了二维层状构型上的横向形核/生长，抑制了Mxene层间可控间隙上的苔藓/树枝状Li。由于高电子传导性和较大的层间距，快速的电荷转移导致小的接触/转移电阻和锂离子在Mxene表面的快速扩散，从而使Li通过层间嵌插成核/生长的势垒大大降低，并减少了SEI的形成。如果成功，与纯Li箔相比，以镍锰钴氧化物(NMC)或镍钴氧化铝(NCA)为正极的全电池将显示出更好的容量保持率。该项目将提供一个范例，通过集成2D材料设计、模拟和电化学性能验证来设计一种新的、可靠的抑制枝晶的锂金属电极。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Energy storage at an affordable cost has emerged as one of the challenging issues for the energy sector, being critical for a wide range of applications ranging from electric vehicles to grid storage of renewable energies. The rapidly growing demand in high energy-density batteries for electrical vehicles requires scientists to explore new electrode materials that can deliver higher energy capacity. To this end, Li metal is attracting extensive attention in next-generation lithium-ion batteries. However, unstable and irreversible Li plating/stripping can result in a short battery lifetime and a serious safety issue related to the possible dendrite growth of lithium. This fundamental research project seeks to develop a hybrid electrode that is composed of novel 2-dimensional carbide or nitride nanomaterials called MXenes as a substrate to construct composite lithium metal anodes. The coated 2D MXene layers provide large volume of empty space between layers, better conductivity, and suppression of the dendrite growth. This approach of material design is also amenable to large-scale manufacturing methods for making battery anodes. If successful, the developed Li-metal electrode can be applied in various liquid-electrolyte and solid-state batteries. The experimental design, problem solving, and performance analysis of this project will be integrated with educational outreach for undergraduate students in the science, technology, engineering and math (STEM) fields particularly in energy storage field of materials science and engineering via a series of ‘Interest-Inspiring’ research experiences and courses. Two-dimensional nanomaterials such as MXenes display intense promise for lithium batteries due to the efficient and fast ion transport between layers and large surface areas available for improved ion adsorption and faster surface redox reactions. The open ion transport channels in MXenes shorten ion diffusion pathways and enable fast ion transport. In addition, they can act as functional substrates for incorporating various active materials for lithium ion batteries, improving the total capacity of the electrodes and enhancing the overall performance. The technical goal of this research project is to design a scalable 2D MXenes such as Ti3C2Tx stacks inter-layer-calated thin Li metal hybrid anode, which shows a highly reversible plating/stripping with a low overpotential upon long cycles in lithium ion batteries. The large surface area of the multi-layer MXene stacks with high mechanical flexibility ensures a high-capacity and reliable Li nucleation/growth upon plating and stripping. The highly reversible Li through the confined 2D configuration reduces the dead Li and electrolyte consumption by forming a thin solid electrolyte interphase (SEI) layer. The mossy/dendritic Li on the controllable inter-spaces between MXene layers is suppressed due to the lateral nucleation/growth on the 2D layered configuration, which is studied using in-situ observations and modeling. The fast charge-transfer due to the high electron conductivity and large inter-layer spacing leads to small contact/transfer resistances and rapid lithium ion diffusion on the MXene surface with terminations, enabling a drastically lowered energy barrier for Li nucleation/growth through inter-layer-calation as well as less SEI formation. If successful, the full cell batteries paired with nickel-manganese-cobalt oxide (NMC) or nickel-cobalt-alumina (NCA) as cathode will exhibit an improved capacity retention when compared with pure Li foil. This project will provide an example to design a new, reliable Li metal electrode with dendrite suppression by integrating 2D material design, simulation and electrochemical performance validation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.