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

以可承受的成本进行储能已成为能源部门面临的挑战之一，对于从电动汽车到可再生能源电网储能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，这要求科学家们探索能够提供更高能量容量的新电极材料。为此，Li金属在下一代锂离子电池中引起广泛关注。然而，不稳定且不可逆的Li镀覆/剥离可导致短电池寿命和与锂的可能枝晶生长相关的严重安全问题。该基础研究项目旨在开发一种混合电极，该电极由称为MXenes的新型二维碳化物或氮化物纳米材料组成，作为构建复合锂金属阳极的基底。经涂覆的2D MXene层在层之间提供大体积的空空间、更好的导电性和对枝晶生长的抑制。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，开发的锂金属电极可以应用于各种液体电解质和固态电池。该项目的实验设计，问题解决和性能分析将通过一系列“探索-学习”研究经验和课程，与科学，技术，工程和数学（STEM）领域的本科生教育推广相结合，特别是在材料科学和工程的储能领域。二维纳米材料如MXenes显示出对锂电池的强烈希望，这是由于层间有效和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。MXene中开放的离子转运通道缩短了离子扩散途径，并实现了快速离子转运。此外，它们还可以作为功能基底，用于掺入锂离子电池的各种活性材料，提高电极的总容量并提高整体性能。本研究项目的技术目标是设计一种可扩展的2D MXene，如Ti3C2Tx堆叠层间加热的薄Li金属混合阳极，其在锂离子电池中显示出高度可逆的电镀/剥离，在长循环时具有低过电位。具有高机械柔性的多层MXene堆叠的大表面积确保了在电镀和剥离时的高容量和可靠的Li成核/生长。通过受限的2D构型的高度可逆的Li通过形成薄的固体电解质中间相（SEI）层来减少死Li和电解质消耗。MXene层之间的可控间隙上的苔藓状/树枝状Li由于2D层状配置上的横向成核/生长而被抑制，这是使用原位观察和建模来研究的。由于高电子电导率和大的层间间距导致的快速电荷转移导致小的接触/转移电阻和具有终端的MXene表面上的快速锂离子扩散，使得能够通过层间calation以及更少的SEI形成大幅降低Li成核/生长的能垒。如果成功的话，与纯锂箔相比，与镍锰钴氧化物（NMC）或镍钴氧化铝（NCA）作为阴极配对的全电池将表现出改善的容量保持率。该项目将提供一个通过集成2D材料设计、模拟和电化学性能验证来设计具有枝晶抑制的新型可靠锂金属电极的范例。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值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.