Ti3C2Tx/MnO2正极在水系锌电池中的电化学性能

二氧化锰(MnO₂)材料具有比容量大、电极电位高、储量丰富以及价格低廉等优势，成为水系锌电池正极最受关注的一类材料，然而其仍然存在着结构稳定性差和电化学储存机理复杂的问题。因此，我们通过两步合成法制备了一种花苞状结构的MnO₂负载在Ti₃C₂T_x表面形成Ti₃C₂T_x/MnO₂复合材料，通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对复合样品的结构、成分和形貌进行表征。通过将Ti₃C₂T_x/MnO₂复合材料作为正极，与锌负极匹配组装成水系锌电池，研究了其分别在2 mol·L^-1 ZnSO₄、2 mol·L^-1 ZnSO₄+0.1 mol·L^-1 MnSO₄、30 mol·L^-1三氟甲基磺酸四乙基铵(TEAOTf)+1 mol·L^-1三氟甲烷磺酸锌(ZnOTf)和3 mol·L^-1 ZnOTf四种电解液中的电化学性能。结果表明，Ti₃C₂T_x/MnO₂在2 mol·L^-1 ZnSO₄中的比容量较高，但循环稳定性很差。将TEAOTf盐和ZnOTf盐共溶于水中，设计了一种新型的含惰性阳离子的超高浓度盐包水电解液(30 mol·L^-1 TEAOTf+1 mol·L^-1 ZnOTf)，不仅提高了Ti₃C₂T_x/MnO₂材料的可逆性，而且有效抑制了电极材料在循环过程中的溶解。

Electrochemical Performance of Ti3C2Tx/MnO2 Cathode in Aqueous Zinc Ion Batteries

Owing to the advantages of large specific capacity, high work potential, rich reserves, and low price, manganese dioxide (MnO₂) material has become the most potential material for the cathode in aqueous zinc batteries (AZBs). However, it still has problems with poor structural stability and complex electrochemical storage mechanism. Herein, a kind of Ti₃C₂T_x/MnO₂ composite material based on bract-liked structural of MnO₂ deposited on Ti₃C₂T_x was prepared by a two-step method, and the structure, composition, and morphology of the composite were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The zinc storage performance of Ti₃C₂T_x/MnO₂ cathode were evaluated in different aqueous electrolyte (2 mol·L^-1 ZnSO₄, 2 mol·L^-1 ZnSO₄+0.1mol·L^-1 MnSO₄, 30 mol·L^-1 tetraethylammonium triflate (TEAOTf)+1 mol·L^-1 ZnCF₃SO₃ (ZnOTf), 3 mol·L^-1 ZnOTf), respectively. As a result, Ti₃C₂T_x/MnO₂ cathode displayed two obvious discharge platforms in 2 mol·L^-1 ZnSO₄ and 2 mol·L^-1 ZnSO₄+0.1 mol·L^-1 MnSO₄ solution, which is attributed to the co-insertion of H⁺ and Zn²⁺ due to the weak acidic electrolyte. The initial platform region at 1.0 V occurred in the first step is the insertion of H⁺, and the subsequent reaction is the insertion of Zn²⁺ into Ti₃C₂T_x/MnO₂ electrode. However, in the neutral of 3 mol·L^-1 ZnOTf and 30 mol·L^-1 TEAOTf+1 mol·L^-1 ZnOTf electrolyte, the insertion of H⁺ into the Ti₃C₂T_x/MnO₂ cathode hardly appears, and the obtained discharge capacity may mainly come from the intercalation of Zn²⁺. Moreover, the utilization of ultra-high concentration electrolyte could not only improve the reversibility of Ti₃C₂T_x/MnO₂ electrode material but also effectively inhibit the dissolution of electrode material in the cycling process (78.2% capacity retention after 100 cycles at 0.2 A·g^-1).