Advanced Energy Materials:MXene-Ti3C2 High performance lithium ion conductor based on mesoporous nanosheets

With the rapid growth of electric vehicles mobile electronic devices

is in urgent need of providing safe rechargeable lithium-based batteries. Solid polymer electrolytes (such as polyepoxypropane polyethylene oxide) are expected to replace flammable liquid electrolytes brittle inorganic solid electrolytes due to their easy processing similar working mechanism to inorganic solid electrolytes. However pure polymer electrolytes usually exhibit room temperature ionic conductivity (10-5-10-10 scm-1) low Young's modulus (less than 0.4 MPa). In order to promote the transport of Li in solid polymer electrolyte an effective strategy is to add zero dimensional (SiO2 TiO2 Al2O3) one-dimensional (li0.33la0.557tio3) two-dimensional (graphene oxide mxene-ti3c2) inorganic fillers to the polymer matrix to produce inorganic / polymer solid electrolyte. For example when a new two-dimensional material mxene-ti3c2 is added to PEO the ionic conductivity of solid polymer electrolyte can be increased to 7.0 × 10-10 scm-1 which is five times of that of pure PEO electrolyte (1.4 × 10-10 scm-1). So far more than 20 kinds of mxenes with rich surface functional groups (- Oh - F - CL) have been developed which provides a great opportunity for the development of solid polymer electrolytes containing mxenes with high Li conductivity. However mxene-ti3c2 has a high conductivity of about 103 scm-1 is easy to agglomerate which limits its application in polymer electrolytes.

Professor Yang Shubin's research group of Beijing University of Aeronautics Astronautics has developed an effective method to prepare mxene-ti3c2-based mesoporous silica nanosheets (mxene-msio2) with swich structure independent two-dimensional characteristics low conductivity through cetyltrimethylammonium bromide induced mxene-ti3c2 dispersion in-situ controllable hydrolysis of tetraethyl orthosilicate on the surface of nanosheets It can improve the ionic conductivity of polyepoxy propane. Mxene-ti3c2 is electronegative because of its abundant functional groups (- F - OH). Cationic surfactant cetyltrimethylammonium bromide is self-assembled on the surface of ultrathin nanosheets by electrostatic attraction. Through in-situ hydrolysis of tetraethyl orthosilicate silica was uniformly grown on the surface of mxene-ti3c2 monodisperse mxene based mesoporous silica nanosheets with swich structure were obtained. The thickness of mesoporous silica layer can be easily adjusted by changing the ratio of TEOS to mxene-ti3c2. The specific surface area of mxene-msio2 is 491.9 m2g-1 which is 16 times higher than that of mxene-ti3c2 (29.4 m2g-1). The electronic conductivity of mxene-msio2 nanosheets is 2.3 × 10-5 s cm-1 which is 7 orders of magnitude lower than that of mxene-ti3c2 (1.4 × 103 s cm-1). As shown in Fig. 1a mxene-msio2 was added to polyepoxy propane to prepare polymer solid electrolyte containing mxene-msio2. Due to the rigid hydrogen bonds the polyfluoropropylene can be dispersed uniformly on the surface of the matrix. The results of nanoindentation show that the young's modulus of polymer solid electrolyte containing mxene-msio2 is also significantly enhanced due to the formation of a large number of hydrogen bonds. The results show that the ionic conductivity of solid polymer electrolyte containing mxene-msio2 is affected by two-dimensional filler lithium salt content the optimal value is 4.6 × 10-4 scm-1 which is twice as high as that of silica particles / poly (propylene oxide) solid electrolyte higher than most solid polymer electrolytes. The high ionic conductivity is attributed to the formation of a large number of Lewis acid-base interactions between mxene-msio2 LiTFSI with high specific surface area rich functional groups (hydroxyl fluoro groups) which constructs a fast Li transport pathway at the interface between mxene-msio2 polypropylene oxide (Fig. 1a). When the polymer solid electrolyte containing mxene-msio2 was applied in the lithium metal all battery its electrochemical performance was significantly higher than that of the reference sample (Fig. 1b). The researchers of

believe that through this simple strategy a series of mxene containing solid polymer electrolytes with high ionic conductivity can be produced for high safety lithium metal batteries.

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