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 . The sharing of MXene ‘s development in lithium, sodium and other metal anodes this time is only a part of the published articles, and other articles will be shared later .

Literature 1 :

Flexible Ti 3 C 2 MXene-lithium film with lamellar structure for ultrastable metallic lithium anodes

Nano Energy 39 (2017) 654–661 .

brief introduction

Based unique ductility metal lithium and lubricity, two-dimensional material Beijing University of Aeronautics and Astronautics poplar bin TF using roll-to-roll processing method, to obtain a flexible layered lithium -Ti . 3 C 2 composites. Since the rolling process has undergone several stacked, the entire structure of a multilayer composite film material exhibits wrinkles, metal lithium located in an interlayer, a scanning electron microscope, the morphology can be seen clearly Nanocrystalline multilayer sheet. These lithium-philic sheets can prevent the oxidation of lithium metal. Through XPS testing, it was found that a small amount of Ti-Li bonds were generated as nucleation sites for lithium deposition in the Ti 3 C 2 nanosheets . In the composite film, the lithium-philic atomic layer acts as an artificial SEI film.

The functional groups adsorbed on the Ti 3 C 2 MXene nanosheets are lithium- philic . Lithium metal grows in parallel in the nano-gap to prevent its vertical growth from piercing the diaphragm . This can be by in situ transmission electron microscopy confirmed , lithium preferentially deposited of Ti . 3 C 2 interlayer nanosheet. When the lithium- Ti 3 C 2 composite material is used as a negative electrode , it can be stably cycled more than 200 times at a current of 1 mA / cm 2 and can still be stably charged and discharged at a current of 5 mA / cm 2 . The composite material shows a markedly low overpotential (at 1.0 mA / cm2 when 32 mV ), good rate capability , at 3.0 mA / cm & lt 2 when 53 is mV . This is because the conductive Ti 3 C 2 can not only reduce the local current during lithium deposition, but also provide nucleation sites for lithium deposition and a buffer space for volume changes during cycling .

Literature 2 :

MXene Aerogel Scaffolds for High-Rate Lithium Metal Anodes

Angew . Chem. Int. Ed. 2018, 57, 15028–15033.

brief introduction

Luo Jiayan‘s research group of Tianjin University adopted MXene aerogel as the carrier of lithium metal anode, and achieved very good results. In this paper, the GO dispersion liquid and the MXene dispersion liquid were evenly mixed, HI acid was added for ultrasonic treatment for 5 min , and then reacted at 80 ° C for 6 hours in a reactor to form a self-assembled MXene hydrogel, and finally freeze-dried to obtain an aerogel. It explains MXene airgel high performance as a lithium base negative electrode metal stents mechanism: First, MXene nanosheet surface rich in oxygen functional groups may induce uniform nucleation of lithium; secondly, interdigitated MXene nanoplatelets only has high The electronic conductivity also has a fast ion transmission path, which can promote the growth of lithium; in addition, the interconnected voids of the aerogel can serve as a stable carrier for lithium loading, alleviating the volume expansion of lithium metal.

When the content of MXene increased to 70% , the aerogel M / G-70 had the most stable Coulomb efficiency. To verify the lithium affinity of the MXene nanosheet functional group, the authors compared the nucleation overpotential of M / G-70 aerogel and rGO aerogel. The results show that the overpotential of M / G-70 aerogel is much smaller than that of rGO aerogel. Importantly, in terms of greater current density and surface capacity, compared with the performance of rGO aerogel , the coulombic efficiency and cycle stability of M / G-70 aerogel are much better than the performance of rGO aerogel. Compared with a full battery, the performance of M / G-70 is also higher than that of rGO aerogel.

Literature 3 :

Conducting and Lithiophilic MXene / Graphene Framework for High-Capacity, Dendrite-Free Lithium−Metal Anodes

ACS Nano 2019, 13, 14308−14318 .

brief introduction

Wu Zhongshuai team of Dalian Institute of Chemical Physics , Chinese Academy of Sciences , prepared MXenes and GO composite aerogel ( MGO film ) by freeze-drying method , compressed into MGO film, and then reduced it to conductive lithium- philic three-dimensional MG film. In this way, an MG-Li composite anode material is prepared, which can be used as a dendrite-free lithium metal anode. Thanks to its high specific surface area ( 259 m 2 / g ) and ultra-light characteristics, plus a large amount of lithium- philic MXene distributed in the 3D porous conductive structure, lithium nucleation and growth are well limited to In the conductive skeleton, it has a Coulomb efficiency of up to 99% and an ultra-long life of 2700 h . At an ultra-high current density of 20 mA / cm 2 , 230 charge-discharge cycles remain stable and have an ultra-high lithium storage capacity (about 92% of theoretical capacity ) .

Literature 4 :

Flexible and Freestanding Silicon / MXene Composite Papers for High-Performance Lithium-Ion Batteries

ACS Nano 2019, 13, 14319−14328 .

brief introduction

With the deepening of the understanding of the three-dimensional host, once lithium dendrites are formed , the open three-dimensional structure cannot completely solve the problem of dendrites . Inspired by the structure of the building, a three-dimensional porous Ti 3 C 2 T x -rGO film with lithium affinity was prepared as a stable framework for the realization of a safe alkali metal (Li or Na) anode . Graphene oxide ( GO ) was used to construct a porous structure between the MXene sheets under the microscopic explosion reaction at high temperature, and the metal lithium or sodium was successfully compounded with the 3D porous Ti 3 C 2 T x -rGO film by melt infusion . As a rigid skeleton , MXene with good mechanical properties can alleviate the volume expansion of the metal anode in the cycle, and act as an artificial SEI film to prevent the growth of dendrite . Theoretical calculations revealed the formation of Ti-Li / Na ,O-Li / Na and F-Li / Na mixed covalent / ionic bonds play an important role in the electrochemical deposition of uniform , and induce during cycling Li / Na uniform deposition atom , and ultimately the 2400 H ( 100 days, Li ) and 2000 h ( Na ) ultra-long cycle .

Literature 5 :

Inter-layer-calated Thin Li Metal Electrode with Improved Battery Capacity Retention and Dendrite Suppression

Nano Lett. 2020, 20, 4, 2639–2646.

brief introduction

Herein by binderless / additive process of the multilayer MXene stacked laminated on the copper foil, then rolling by inverting the MXene transferred to Li on the sheet, the thickness can be designed according to needs, MXene excellent conductivity and spacing layer provides The fast Li + / electron transport channel, the layered structure limits the growth of lithium in the vertical direction, thereby greatly slowing the growth of dendrites .

Literature 6 :

Flexible and Free-Standing Ti 3 C 2 T x MXene @ Zn Paper for Dendrite-Free Aqueous Zinc Metal Batteries and Nonaqueous Lithium Metal Batteries

ACS Nano 2019, 13, 11676−11685.

brief introduction

Previous literature has shown that Zn can be used as an additive to inhibit the formation of nuclei in the growth of lithium dendrites , thereby improving the coulombic efficiency of lithium metal batteries. The team of Feng Jinkui of Shandong University , on the basis of flexible, self-supporting, highly conductive MXenes paper, prepared a three-dimensional structure of Ti 3 C 2 T x MXene @ Zn paper by a simple electrochemical deposition method . The phase diagram of Li-Zn alloy shows that metallic zinc can react with lithium to form LiZn alloy solid solution, indicating that Ti 3 C 2 T x MXene @ Zn paper has good lithium affinity, and the solid solution formed on the surface layer can reduce the hindrance of nucleation driving force. The three-dimensional structure can be used as a buffer layer for Li volume changes during the deposition / dissolution process . Compared with copper foil, Ti 3 C 2 T x MXene @ ZnThe Coulomb efficiency is significantly different ( 97.69 % in 600 cycles ) ( Cu foil 120 cycles less than 90 %) . The morphology change process, and Cu compared to the rough surface of the electrode, of Ti . 3 C 2 T X MXene a Zn @ in . 1 mA / cm & lt 2 of 200 was not observed after significant dendrite cycles, indicating of Ti . 3 C 2 T X MXene a Zn @ paper inhibiting Li dendrite aspect efficacy .

Literature 7 :

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.

brief introduction

In view of the role of Zn , according to the element replacement method for preparing Zn -based MAX and the corresponding MXene , MXene ( Zn-MXene ) with a single zinc atom fixed by etching Ti 3 AlC 2 MAX in a molten salt of ZnCl 2 was prepared . After spraying and rolling process, by controlling the Zn-MXenes amount of ink into a further thickness may be controlled to obtain 1.5-60 um of Zn-MXene film . SEM image display metal lithium tends Zn-MXene surface homogeneous nucleation, the planar active zinc site to guide the lithium in the nucleus growth vertical, form a block lithium . The Zn-MXene structure exhibited 11.3 ± 0.1 mVLow overpotential, long cycle life ( 1200 H ) and up to 40 mAh / cm & lt 2 Depth deposited - stripping ability , at 10C exhibits a up to 500 good performance cycles. In addition, based on the mature rolling technology, the Zn-MXene film and the corresponding lithium anode can be amplified and applied to future lithium battery development .

Source: MXene notes

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