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

GRAPhMAX的目标是开发一种高性能的锂和钠离子电池有机阳极，利用石墨烯酸作为活性电极，并通过与MXenes形成共价和非共价异质结构，探索其作为高面积质量的独立膜的操作。MXenes和石墨烯酸在仔细结合时，都可以从相互协同的特性中受益匪浅。MXenes的性质受到其表面终止的强烈影响，理论上可能提供类似金属的导电性。作为电极，它们的电导率可以达到15100 S/cm，而石墨烯酸只能达到0.25 S/cm。他们还展示了他们在高面质量电极方面的潜力。然而，在能力方面，MXenes显示出较低的值；例如，在0.03 A/g时，Ti2C的电压低于200 mAh/g。Ti3C2是研究最广泛的MXene，在0.03 A/g时的容量约为100 mAh/g。只有严格选择单层电极制备，在0.41 A/g下，由于层的膨胀，更大的表面积，以及MXene的氧化活性中心最大限度地暴露于电解质离子，容量才可能达到410 mAh/g。相反，之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，但到目前为止还无法获得独立的薄膜和厚度持久性。在此基础上，我们假设石墨烯酸/MXene异质结构可以从它们的互补资产中受益，从而产生深远的协同作用：MXenes的高导电性及其成膜特性可能会增强其异质结构中与石墨烯酸的电荷转移和膜稳定性，从而使独立的高性能石墨烯酸电极具有更高的面质量。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，以制备具有最佳质量比的酸石墨烯/MXene独立异质结构，并通过结构表征和电化学测试筛选最终所需的性能。

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.