Thickness - independent capacitance of vertically aligned liquid-crystalline MXenes
Thickness - independent capacitance of vertically aligned liquid-crystalline MXenes
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DOI：
10.1038/s41586-018-0109-z
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发表时间：
2018-05-17
期刊：
影响因子：
64.8
通讯作者：
Yang, Shu
中科院分区：
文献类型：
--
作者：
Xia, Yu;Mathis, Tyler S.;Yang, Shu
具有高能量和功率密度的厚电极膜的可扩展和可持续制造对于运输和固定电网中应用的电化学能量的大规模存储至关重要。二维纳米材料由于具有较大的表面积与体积比且缺乏固态扩散，已成为追求高能量和功率密度的电极材料的主要选择(1,2)。然而，传统的电极制造方法通常会导致二维纳米材料重新堆叠，从而限制了厚膜中的离子传输，并导致系统的电化学性能高度依赖于薄膜的厚度(1-4)。促进离子传输的策略，例如通过插层（5-8）增加层间距或通过设计纳米结构（9,10）引入薄膜孔隙率，会导致材料体积能量存储低，以及复杂而冗长的离子传输路径，从而阻碍高充放电速率下的性能。二维薄片的垂直排列可实现定向离子传输，从而在厚膜中实现与厚度无关的电化学性能(11-13)。然而，到目前为止，仅报道了有限的成功(11,12)，并且在处理厚度接近或超过 100 微米工业标准的二维纳米材料薄膜时，减轻性能损失仍然是一个重大挑战。在这里，我们演示了与垂直排列的二维碳化钛 (Ti3C2TX) 薄膜厚度无关的电化学储能，这是一种来自 MXene 家族的材料（过渡金属 (M) 的二维碳化物和氮化物，其中 X 代表碳或氮）。垂直排列是通过机械剪切 Ti3C2TX 的盘状层状液晶相来实现的。由此产生的电极薄膜表现出优异的性能，几乎与高达 200 微米的薄膜厚度无关，这使得它们对于储能应用极具吸引力。此外，这里提出的自组装方法是可扩展的，可以扩展到涉及定向传输的其他系统，例如催化和过滤。
The scalable and sustainable manufacture of thick electrode films with high energy and power densities is critical for the large-scale storage of electrochemical energy for application in transportation and stationary electric grids. Two-dimensional nanomaterials have become the predominant choice of electrode material in the pursuit of high energy and power densities owing to their large surface area-to-volume ratios and lack of solid-state diffusion(1,2). However, traditional electrode fabrication methods often lead to restacking of two-dimensional nanomaterials, which limits ion transport in thick films and results in systems in which the electrochemical performance is highly dependent on the thickness of the film(1-4). Strategies for facilitating ion transport such as increasing the interlayer spacing by intercalation(5-8) or introducing film porosity by designing nanoarchitectures(9,10)-result in materials with low volumetric energy storage as well as complex and lengthy ion transport paths that impede performance at high charge-discharge rates. Vertical alignment of two-dimensional flakes enables directional ion transport that can lead to thickness-independent electrochemical performances in thick films(11-13). However, so far only limited success(11,12) has been reported, and the mitigation of performance losses remains a major challenge when working with films of two-dimensional nanomaterials with thicknesses that are near to or exceed the industrial standard of 100 micrometres. Here we demonstrate electrochemical energy storage that is independent of film thickness for vertically aligned two-dimensional titanium carbide (Ti3C2Tx), a material from the MXene family (two dimensional carbides and nitrides of transition metals (M), where X stands for carbon or nitrogen). The vertical alignment was achieved by mechanical shearing of a discotic lamellar liquid-crystal phase of Ti3C2Tx. The resulting electrode films show excellent performance that is nearly independent of film thickness up to 200 micrometres, which makes them highly attractive for energy storage applications. Furthermore, the self-assembly approach presented here is scalable and can be extended to other systems that involve directional transport, such as catalysis and filtration.