Graphene acid/MXenes heterostructures for lithium- and sodium-ion batteries. (Acronym GRAPhMAX)

GRAPhMAX的目标是开发用于锂和钠离子电池的高性能有机阳极，利用石墨烯酸作为活性电极，并通过开发MXenes的共价和非共价异质结构，探索其在高面积质量下作为独立膜的操作。MXene和石墨烯酸在仔细组合时都可以从相互协同的性质中受益匪浅。MXene的性质受到其表面终止的强烈影响，并且在理论上可以提供类似金属的导电性。作为电极，它们的电导率可以达到15,100 S/cm，而石墨烯酸仅达到0.25 S/cm。它们还证明了它们用于高面积质量电极的潜力。然而，在容量方面，MXene显示出较低的值;例如，Ti 2C在0.03 A/g下低于200 mAh/g。Ti 3C 2是研究最广泛的MXene，在0.03 A/g下显示出约100 mAh/g的容量。只有在严格选择用于电极制备的单层之后，由于层膨胀、更大的表面积以及MXene的氧化还原活性中心对电解质离子的最大暴露，容量才可以在0.41 A/g下达到410 mAh/g。相反，先前报道的石墨烯酸的容量是在整个合成过程中没有任何层厚度选择的情况下获得的，但是自支撑膜和厚度持久性特性迄今为止是无法实现的。在此基础上，我们假设石墨烯酸/MXene异质结构可以受益于它们的互补资产，从而产生深刻的协同作用：MXene的高导电性及其成膜特性可以增强它们与石墨烯酸的异质结构中的电荷转移和膜稳定性，从而实现具有增加的面积质量的独立的高性能石墨烯酸电极。为了实现这一目标，必须开发一种有效的杂交方法，包括共价和/或非共价方法，用于制备相对于通过结构表征和电化学测试筛选的最终所需性质具有最佳质量比的石墨烯酸/MXene自支撑异质结构。

The aim of GRAPhMAX is the development of a high-performance organic anode for Li and Na-ion batteries, exploiting graphene-acid as the active electrode and explore its operation as a free-standing film at high areal masses, by developing covalent and non-covalent heterostructures with MXenes. MXenes and graphene acid both can, when combined carefully, greatly benefit from mutually synergetic properties.MXenes’ properties are strongly influenced by their surface termination and, in theory, may provide a metal-like conductivity. As electrodes, they can reach a conductivity of 15,100 S/cm, while graphene acid only reaches 0.25 S/cm. They have also demonstrated their potential for high areal mass electrodes. However, capacity-wise, MXenes show low values; Ti2C, for example, stands below 200 mAh/g at 0.03 A/g. Ti3C2, the most widely studied MXene, shows capacities around 100 mAh/g at 0.03 A/g. Only after strict selection of monolayers for electrode preparation, the capacity may reach 410 mAh/g at 0.41 A/g, due to layer expansion, larger surface area, and maximum exposure of MXene’s redox-active centers to the electrolyte ions. On the contrary, the previously reported capacities for graphene acid were obtained without any layer-thickness selection during the whole synthetic procedure, but free-standing films and thickness-persistent properties have been so far unattainable. On this basis, we hypothesize that graphene acid /MXene heterostructures could benefit from their complementary assets, leading to profound synergism: the high conductivity of MXenes and their film-forming properties may enhance charge transfer and film stability in their heterostructures with graphene acid, enabling free-standing high-performance graphene acid electrodes with increased areal mass. To achieve this objective, an efficient hybridization methodology must be developed involving covalent and/or non-covalent approaches for preparing graphene acid/MXene free-standing heterostructures with optimum mass ratio with respect to the final required properties screened by structural characterization and electrochemical testing.