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Will Mxenes become the next generation of lithium battery electrode materials?

2018-10-24 来源:亚科官网
24 October 2018
With the popular of wearable devices, miniaturized and flexible electronic devices are increasingly sought after by people, and thus become a research hotspot. This also puts new demands on electrode materials: how to develop a new flexible electrode material with high density and high volume energy density. Will the new two-position nanomaterial Mxenes with many advantages be the next generation of lithium-ion battery electrode materials? Let's analyze it together.
What is Mxenes?
MXene is a class of two-dimensional inorganic compounds in materials science consisting of transition metal carbides, nitrides or carbonitrides of several atomic layers.
Mn+1AXn, n=1–3
?   ?M stands for early transition metals such as Sc, Ti, Zr, V, Nb, Cr or Mo;
?   ?A usually represents the chemical elements of the third main group and the fourth main group;
?   ?X stands for C or N element.
It is usually obtained by selective etching of the A element in the MAX ceramic powder by HF. The synthesized MXene has a similar accordion form, and is a multilayer MXene, or a thin layer MXene (less than 5 layers). Due to its layered structure, large density and specific surface area, high conductivity and wettability, and relatively good chemical stability, MXenes are widely used in ion batteries, supercapacitors, electrocatalysis, and sensors.
What is the performance of Mxenes as a lithium battery electrode material?
The lithium battery mainly includes a positive electrode, a negative electrode, an electrolyte, and a separator.
(1) positive electrode, the main performance to be guaranteed includes conductance (reduced internal resistance), diffusion (guaranteed reaction kinetics), longevity, safety, and proper processing performance (the specific surface area is not too large, reducing side reactions, and serving safety). The existing positive electrode materials are lithium iron phosphate, ternary materials, lithium manganate, etc.;
(2) The negative electrode not only meets the kinetic requirements of lithium diffusion, but also solves the safety problems caused by the increased tendency of lithium dendrite formation. At present, the dominant anode material on the market is still graphite, the surface of which is sensitive to electrolyte, and the lithium intercalation reaction has strong directionality;
(3) Separator, ceramic coated diaphragm is highly safe and can consume impurities in the electrolyte, which is particularly effective for improving the safety of ternary batteries
(4) The electrolyte should be characterized by its inability to decompose, high electrical conductivity, and inertness to the positive and negative materials. Usually, various additives against high temperature, flame retardant and overcharge protection, such as T3P, can be added to the electrolyte to improve its safety to some extent.
Whether MXenes is suitable for lithium-ion batteries, and even lithium-sulfur batteries, researchers at the University of Technology, Sydney, Australia have done the research [1]. In lithium-ion batteries, due to the good electrical properties of MXenes and their derivatives, single-layer MXenes (such as Ti2C, Ti3C2) and bimetallic layers MXenes (such as Mo2TiC2, Mo2Ti2C3) have shown in actual experiments and theoretical calculations. Good electrochemical performance. However, the absence of a significant discharge platform, the lower efficiency of the first week and the ease with which the nanolayers are easily stacked affects the further use of MXenes materials. MXenes are often combined with other materials such as metal oxides, metal elements, sulfides, and carbon materials as lithium ion battery electrode materials. In the lithium-sulfur battery, through practical experiments and theoretical calculations, the functional groups on the surface of MXenes have the function of adsorbing polysulfide, thereby inhibiting the shuttle effect of polysulfide in lithium-sulfur batteries and improving the electrochemical performance of lithium-sulfur batteries. Therefore, when MXenes is used as a cathode sulfur carrier, a separator, and materials for improving lithium metal anodes for lithium-sulfur batteries, battery performance is significantly improved.
Therefore, Mxenes has great advantages in electrode materials due to its excellent electrical conductivity, high specific surface area, ability to adsorb polysulfides, and inhibition of dendritic growth of lithium negative electrodes. However, in order to replace graphite as a next-generation lithium-ion battery and lithium-sulfur battery electrode material, there are still many problems to be further solved by researchers.
[1] Xiao Tang, Xin Guo, Wenjian Wu, et al. 2D Metal Carbides and Nitrides (MXenes) as High-Performance Electrode Materials for Lithium-Based Batteries. Advanced Energy Materials, 2018, doi:10.1002/aenm.201801897
Related links: T3P
Edited by Suzhou Yacoo Science Co., Ltd.