Sodium-ion batteries have the advantages of high safety and low cost, which are expected to be applied to large-scale energy storage in smart grids. As the anode material of sodium ion battery, SnS2 has a high theoretical specific capacity, but its first coulombic efficiency is low, which seriously hinders its practical application. Recently, PicoFemto®In-situ electrical sample rod (STM-TEM Holder) helps the School of Environment and Energy of South China University of Technology, Professor Liu Meilin of Georgia Institute of Technology in the United States and Professor Yang Chenghao of South China University of Technology (corresponding author) to make another breakthrough in the research of sodium ion batteries with Sn-based anode materials, the relevant research results were published in the international journal ACS NANO (DOI: 10.1021/acsnano.9b00375) under the title of "Fabrication of SnS2/Mn2SnS4/Carbon Heterostructures for Sodium-Ion Batteries with High Initial Coulombic Efficiency and Cycling Stability.

Researchers have prepared a SnS2/Mn2SnS4/Carbon (SMS/C NBs) heterostructure using a simple and easy wet chemical method and used it to make a negative electrode material for sodium ion batteries. It is found that SMS/C NBs have an initial capacity of 841.2 mAh/g and a first coulombic efficiency of 90.8%. At the same time, it also shows excellent rate performance (at current densities of 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0 A /g, the capacity can reach 752, 604.7, 570, 546.9, 519.7, and 488.7 mAh/g, respectively). In addition, its cycle stability is also good (at 5.0 A/ g current density, 500 cycles, its capacity is still 522.5 mAh/g).

Use PicoFemto®STM-TEM Holder, the researchers fixed SMS/C and Na @ Na2O on Au and W tips respectively as electrodes to build micro-batteries, and studied the microscopic changes of electrode materials during sodiation/desodiation to explore the mechanism of excellent electrochemical properties of materials. They found that the volume expansion rate of the negative electrode material SMS/C was relatively small at about 2min, indicating that the introduction of Mn can obviously prevent the coarsening of nano-scale Sn. Moreover, the volume of the negative electrode material is basically restored to its original size after the sodium removal process. PicoFemto®In-situ sample rods provide strong support for the intuitive, real-time study of this reversible process. In addition, combined with DFT theoretical calculation and in-situ XRD characterization, the researchers found that the SnS2/Mn2SnS4 heterojunction is the key to the good electrochemical performance of SMS/C NBs anode materials. The SnS2/Mn2SnS4 heterogeneous interface can stabilize the reaction intermediate products, prevent the coarsening of the nano-scale Sn0 particles, and ensure the reversible transformation of the alloying, resulting in higher first-time coulomb efficiency and cycle stability. In addition, the combined effect of the SMS and carbon network of the heterostructure can provide an effective channel for the migration of electrons and sodium ions, thereby improving the rate performance.

Original Link: https://pubs.acs.org.ccindex.cn/doi/abs/10.1021/acsnano.9b00375