Abstract
Lithium-ion batteries (LIBs) have been one of the most predominant rechargeable power sources due to their high energy/power density and long cycle life. As one of the most promising candidates for the new generation negative electrode materials in LIBs, silicon has the advantages of high specific capacity, a lithiation potential range close to that of lithium deposition, and rich abundance in the earth’s crust. However, the commercial use of silicon in LIBs is still limited by the short cycle life and poor rate performance due to the severe volume change during Li++ insertion/extraction, as well as the unsatisfactory conduction of electron and Li+ through silicon matrix. Therefore, many efforts have been made to control and stabilize the structures of silicon. Magnesiothermic reduction has been extensively demonstrated as a promising process for making porous silicon with micro- or nanosized structures for better electrochemical performance in LIBs. This article provides a brief but critical overview of magnesiothermic reduction under various conditions in several aspects, including the thermodynamics and mechanism of the reaction, the influences of the precursor and reaction conditions on the dynamics of the reduction, and the interface control and its effect on the morphology as well as the final performance of the silicon. These outcomes will bring about a clearer vision and better understanding on the production of silicon by magnesiothermic reduction for LIBs application.
Highlights
Silicon-Based Negative Electrode Materials: Advantages and ChallengesThe development of green and sustainable energy technologies has become one of the most important issues in the world facing the problems of energy and environment resulting from the massive use of fossil fuel based technologies
A good example is lithiumion batteries (LIBs) which play a vital role in portable electrical devices for years and are being increasingly applied in electric vehicles and electricity storage banks
There are still some obstacles limiting the mass production of Si by magnesiothermic reduction (MTR), including the not high-enough Si yield, and the side reactions during the reduction
Summary
The development of green and sustainable energy technologies has become one of the most important issues in the world facing the problems of energy and environment resulting from the massive use of fossil fuel based technologies. The costly equipment, complex production process, and a very low production yield all limit the scale production of nano Si by CVD Another route is the electrochemical reduction of Si in molten salt, which could realize relatively high purity Si products with morphology-controllable nanostructures at lower temperatures (generally 650–900◦C) in comparison with the carbothermic reduction method (Jiang et al, 2020). If the pressure of Mg vapor is not high enough, especially in the interfacial region of SiO2 and MgO, Mg silicates such as Mg2SiO4 and MgSiO3 may form as shown in Figure 3D via Eq 5 and 6 These reactions would consume the reactant SiO2 and reduce the yield of Si. On the other hand, Mg silicates are detrimental to the electrochemical performance in batteries, which are not easy to remove thoroughly. Almost all the biologically originated silica materials contain carbon, which may form SiC during reduction where local temperature is quite high, and the content of SiC may worsen the electrochemical properties of Si, leading
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