Application-MXene is used in lithium-sodium metal anodes-③

Research background

Due to its unique physicochemical properties, MXene has been extensively studied and involves multiple fields . Metal lithium is expected as a next generation high energy density battery negative electrode material, a lithium sulfur, lithium-air battery. However, the charge-discharge cycle, lithium is repeated due to uneven deposition / dissolution of metal lithium negative electrode surface easily grows lithium dendrites, lithium dendrites loose structure, easy off electrochemically inactive form of " dead lithium " , leading to cell rapid decay reversible capacity, dendrite but also can cause the battery to short circuit , metal these problems limit the lithium applying the electrodes in the secondary battery. Specific structural design 3D host material, is expected to be no branches crystal growth to achieve higher security than the flexible energy of a lithium negative electrode metal. MXene is an emerging two-dimensional material, which has high conductivity and low diffusion barrier for lithium ions, and the groups adsorbed on the surface are lithium- philic . This time sharing MXene in lithium metal anode from the perspective of solid electrolyteThe development of is only a part of the published articles, and later share other articles .

Literature 1 :

2D MXene-containing polymer electrolytes for all-solid-state lithium metal batteries

Nanoscale Adv., 2019, 1, 395 .

brief introduction

In order to solve the problems of lithium metal, in addition to modifying and modifying the lithium metal itself, you can also start from the electrolyte , that is, use a solid electrolyte to replace the usually toxic and flammable organic electrolyte, however, brittleness and interface problems, The application of inorganic solid electrolytes in lithium metal batteries is limited , while the lightweight and flexible polymer electrolytes face the problem of low electrical conductivity at room temperature. Combining the advantages of the two, that is, using inorganic additives to improve the conductivity of polymer electrolytes, has become a feasible solution.

In this paper , a flexible, MXene -based polymer electrolyte membrane was prepared by liquid stirring and mixing at room temperature, dropping onto a PTFE substrate and evaporating . Wherein [EO] / [of Li + ]  ratio is fixed at 20 , according to the relevant literature, when the value of this ratio, the entire PEO solution-coated film having the highest ionic conductivity. Designed a series of different MXene content of PEO groups sample was not added MXene of PEO 20 is -LiTFSI electrolyte is used as comparison test, tested MXenes conductivity of polymer electrolyte base with MXenes where the content, temperature change, because PEO melted It was found that there was a change in the slope of the curve at ~ 45–50 ° C. Constant at different temperatures, with the conductivity are MXenes increasing content increases, the MXenes content ofAt 0.4wt% , the electrical conductivity reached the maximum at 60 ℃ and 28 ℃ . If the content of MXenes is increased , the conductivity will show a downward trend. Since MXenes good dispersibility, hydrophilicity, electronegativity surface and a functional group adsorbing to the PEO molecular chain interactions needed to add MXenes content is much lower than some other reports of an inorganic material additive, showed MXene lifting conductivity It is very effective. Although MXenes has excellent electrical conductivity, it cannot form a seepage path because of its very small content . Its electronic conductivity is negligible and can be used as a polymer electrolyte .

Literature 2 :

MXene-Based Mesoporous Nanosheets Toward Superior Lithium Ion Conductors 

Adv. Energy Mater. 2020, 1903534 .

brief introduction

Considering the low ionic conductivity and low Young‘s modulus of polymer electrolytes at room temperature, it is often necessary to add inorganic fillers . Beijing University of Aeronautics and Astronautics material poplar bin TF , by the surfactant cetyl trimethyl ammonium bromide of induction , electrostatic adsorption assembly so that the TEOS in MXene a surface controllably hydrolyzed in situ , having a sandwich structure, high specific surface area and dimensional characteristics of the preparation MXene group via mesoporous silica nano-sheet. The composite structure of this prepared by having a low electrical conductivity, MXene material of the base surface functional groups of (-OH , etc. ) to enhance the lithium salt anion ( TFSI - ) Lewis acid is , thus promoting of Li + in polyethylene oxide (propylene EPPO ) matrix Migration. The resulting solid electrolyte ion conductivity is as high as 4.6x10 -4  S/ cm,  Young‘s modulus of 10.5 MPa , while showing good electrochemical stability.

The ePPO and MXene-mSiO 2 at 150 deg.] C cured, by LiTFSI / PC to form a solid electrolyte system, after swelling, has good fatigue resistance and deformation recovery. The above properties are attributed to the hydrogen bonding between the functional group on the surface of MXene-mSiO 2 and ePPO . PC plays a plasticizing role, allowing the polymer solid electrolyte to conduct ions at room temperature, up to 4.6x10 -4 at room temperature The ionic conductivity of  S / cm , together with good rate performance and cycle stability , expands the application of highly conductive MXenes in the field of solid electrolytes.

Beijing University of Aeronautics and Astronautics Poplar Bin research group around M the X- ENE made progress in series lithium metal anode applications, now part of the literature summarized as follows:

① Flexible Ti 3 C 2  MXene-lithium film with lamellar structure for ultrastable metallic lithium anodes ;  Nano Energy 39 (2017) 654–661.

② Single Zinc Atoms Immobilized on MXene (Ti 3 C 2 Cl x  ) Layers toward Dendrite-Free Lithium Metal Anodes ;  ACS Nano 2020, 14, 891−898.

③ Horizontal Growth of Lithium on Parallelly Aligned MXene Layers towards Dendrite-Free Metallic Lithium Anodes ;  Adv. Mater. 2019, 31, 1901820.

④ Perpendicular MXene Arrays with Periodic Interspaces toward Dendrite-Free Lithium Metal Anodes with High-Rate Capabilities ;  Adv. Funct.  Mater. 2020, 30, 1908075.

⑤ 3D printing dendrite-free lithium anodes based on the nucleated MXene arrays ;  Energy Storage Materials 24 (2020) 670–675 .

⑥ MXene-Based Mesoporous Nanosheets Toward Superior Lithium Ion Conductors ;  Adv. Energy Mater. 2020, 1903534 .

Source: MXene notes 

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