A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte

Two-dimensional transition metal carbides and nitrides, known as MXenes, are currently considered as energy storage materials. A generic Lewis acidic etching route for preparing high-rate negative-electrode MXenes with enhanced electrochemical performance in non-aqueous electrolyte is now proposed. Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of materials that have attracted attention as energy storage materials. MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution; most other MAX phases have not been explored. Here a redox-controlled A-site etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX-phase precursors with A elements Si, Zn and Ga. A negative electrode of Ti3C2 MXene material obtained through this molten salt synthesis method delivers a Li+ storage capacity of up to 738 C g(-1) (205 mAh g(-1)) with high charge-discharge rate and a pseudocapacitive-like electrochemical signature in 1 M LiPF6 carbonate-based electrolyte. MXenes prepared via this molten salt synthesis route may prove suitable for use as high-rate negative-electrode materials for electrochemical energy storage applications.Funding Agencies|National Natural Science Foundation of ChinaNational Natural Science Foundation of China [21671195, 91426304, 51902320, 51902319]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2018M642498]; China Scolarship Council; Agence Nationale de la Recherche (Labex STORE-EX)French National Research Agency (ANR); International Partnership Program of Chinese Academy of Sciences [174433KYSB20190019]; Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang; Ningbo top-talent team program; Fundamental Research Funds for the Central UniversitiesFundamental Research Funds for the Central Universities [YJ201886]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (faculty grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2016-0358]