Koriukina Tatiana, Kotronia Antonia, Halim Joseph, Hahlin Maria, Rosen Johanna, Edström Kristina, Nyholm Leif
The Ångström Advanced Battery Center, Department of Chemistry-Ångström Laboratory, Uppsala University, P.O. Box 538, SE-751 21 Uppsala, Sweden.
Materials Design Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, 58183 Linköping, Sweden.
ACS Omega. 2022 Nov 7;7(45):41696-41710. doi: 10.1021/acsomega.2c05785. eCollection 2022 Nov 15.
The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: TiC . Herein, freestanding TiC MXene films, composed only of TiC MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of TiC -based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the -Ti-C titanium species situated on the surfaces of the MXene flakes, whereas the Ti-C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine TiC MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the -Ti-C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the TiC electrodes. As the capacities of TiC MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the -Ti-C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.
对新型且性能更优的电池材料的追求引发了众多关于在锂离子电池中使用二维负极材料（如MXenes）可能性的研究。然而，即使对于研究最多的MXene：TiC ，其容量的来源以及不同MXene电极所观察到的容量显著变化的原因仍不明确。在此，仅由TiC MXene薄片组成的独立式TiC MXene薄膜被研究作为无添加剂的负极锂离子电池电极，采用锂金属半电池以及计时电位法、循环伏安法、X射线光电子能谱、硬X射线光电子能谱和X射线吸收光谱实验的组合。本研究的目的是确定导致基于TiC 的锂离子电池所观察到的可逆和不可逆容量的氧化还原反应，以及文献中所见容量显著变化的原因。结果表明，可逆容量主要源于涉及位于MXene薄片表面的 -Ti-C钛物种的氧化还原反应，而薄片核心中存在的Ti-C钛保持电惰性。虽然由原始TiC MXene薄片组成的电极获得的可逆容量相对较低，但在制造电极之前将薄片暴露于水和空气后，可观察到显著更高的容量。这归因于MXene薄片表面钛氧化态的变化，导致 -Ti-C表面物种中Ti(II)、Ti(III)和Ti(IV)的浓度增加。在第一个循环中观察到的显著不可逆容量主要归因于TiC 电极中残留水的存在。由于TiC MXene负极的容量取决于 -Ti-C表面物种中Ti(II)、Ti(III)和Ti(IV)的浓度以及水含量，因此在使用不同的制造、预处理和干燥程序时，可以预期不同的容量。
