Conversion of two-dimensional transition metal carbides into oxides for energy storage applications

To address the existential threat of climate change and to meet the clean energy demands of modern society, energy storage research, particularly lithium-ion systems, have emerged as a key technology that must be developed and employed to meet these needs. Two-dimensional (2D) nanomaterials, such as graphene, transition metal dichalcogenides, transition metal carbides and layered vanadium oxides have emerged as strong candidates for high-performing and next-generation battery technologies due to their extraordinary properties conferred by their low dimensionality. Transition metal carbides, known as MXenes, first discovered in 2011, have positioned themselves as ideal anode materials in both lithium-ion and beyond lithium systems. However, in order to further improve state-of-the-art batteries, new cathode materials with increased lithium insertion capacities must be synthesized via novel methods. Over the past few decades bilayered vanadium oxide nanomaterials have quickly become the subject of many academic studies due to their expandable layered structure and possession of vanadium atoms in high oxidation state, allowing this phase to have very high theorical capacity. Here, in this thesis, for the first time, the transformation of vanadium carbide MXene into bilayered vanadium oxide using a chemical oxidant is shown. A new synthetic approach is developed, and the materials characterization and electrochemistry results presented. Interlayer spacings ranging between 9.79 - 13.71 Å are observed, with excellent rate capability and cycling stability demonstrated by Li- and Mg-preintercalated phases. Additionally, to further demonstrate the versatility of this synthesis approach, it was applied to a titanium carbide MXene system to yield a novel and highly ordered layered lithium titanate phase. This thesis lays the groundwork for future studies focused on the transformation of carbide to oxide and the formation of novel MXene-oxide composites and heterostructures. Keywords: energy storage, lithium-ion, MXene, nanomaterials, sol-gel synthesis, Two-dimensional. 为了应对气候变化带来的生存威胁以及满足现代社会对于清洁能源的需求，以锂离子系统为代表的储能技术急需得到深入研发和应用。二维(2D)纳米材料因其低维度带来的非凡特性而受到重点关注，已成为下一代高性能电池技术的候选者，如石墨烯、过渡金属硫化物(TMDs)、过渡金属碳化物(MXenes)和层状钒氧化物。在2011年被首次发现的过渡金属碳化物在锂离子系统和非锂离子系统中都被看作理想的负极材料。但是，要想研发出更先进和优化的电池，我们必须合成出锂离子储存性能更高的新型正极材料。在过去的几十年里，双层钒氧化物(五氧化二钒)纳米材料因其可延展的层状结构和钒的高价态而赢得学术界的广泛兴趣，让我们看到了它在理论上成为高性能正极材料的潜质。本篇论文首次演示和验证了用化学氧化剂将钒碳化物转化为双层钒氧化物的过程。本文提供了新的合成方法并表述了材料特性及电化学实验成果。层间间距呈9.79 – 13.71 埃格斯特朗(Å)，锂-和镁-嵌入态展现出高倍率性能和循环稳定性。另外，为了展现其广泛用途，本文将以上合成方法用于钛碳化物MXene系统并产出一种新型的、高度有序的钛酸锂。本篇论文为从碳化物到氧化物的转化研究和MXene-氧化物异质结构合成物的形成奠定基础。