Hao-wen Jiang,Yu Qin,Yi-ming Nie,Zhi-fang Su,Yun-fei Long,Yanxuan Wen,Jing Su
The strategy of material modification for improving the stability of silicon electrodes is laborious and costly, while the conventional binders cannot withstand the repeated massive volume variability of silicon-based materials. Hence, there is a demand to settle the silicon-based materials’ problems with green and straightforward solutions. This paper presents a high-performance silicon anode with a binder obtained by in situ thermal cross-linking of citric acid (CA) and β-cyclodextrin (β-CD) during the electrode preparation process. The Si electrode with a binder synthesized by the one-pot method shows excellent cycling performance. It maintains a specific capacity of 1696 mAh·g–1 after 200 cycles at a high current of 0.5 C. Furthermore, the carbonylation of β-CD to carbonyl-β-CD (c-β-CD) introduced better water solubility, and the c-β-CD can generate multidimensional connections with CA and Si, which significantly enhances the specific capacity to 1941 mAh·g–1 at 0.5 C. The results demonstrate that the prepared integrated electrode facilitates the formation of a stable and controllable solid electrolyte interface layer of Si and accommodates Si’s repeated giant volume variations.
In next generation lithium-ion batteries (LIBs), silicon is a promising electrode material due to its surprisingly high specific capacity, but it suffers from serious volume changes during the lithiation/delithiation process which gradually lead to the destruction of the electrode structure. A novel fluorinated copolymer with three different polar groups was synthesized to overcome this problem: carboxylic acid, amide, and fluorinated groups on a single polymer backbone. Moreover, a dual cross-linked network binder was prepared by thermal polymerization of the fluorinated copolymer and sodium alginate. Unlike the common chemical cross-linked network with a gradual and nonreversible fracturing, the dual cross-linked network which combines chemical and physical cross-linking could effectively hold the silicon particles during the volume change process. As a result, excellent electrochemical performance (1557 mAh g–1 at a 4 A g–1 current density after 200 cycles) was achieved with this novel reversible cross-linked binder. Further research studies with regard to the influences of fluorine and acrylamide content were conducted to systematically evaluate the designed binder. Moreover, with the help of new binder, the silicon/graphite and silicon oxide/graphite electrode exhibit superb cycle performance with capacity fade rate of 0.1% and 0.025% per cycle over 200 and 700 cycles, respectively. This novel and unsophisticated design gives a result for fabrication of high-performance Si based electrodes and advancement of the realization of practical application.
Due to the excellent theoretical capacity, silicon-based electrodes have been extensively studied to develop high energy-density lithium-ion batteries (LIBs). Nevertheless, the large volume expansion and unfavorable interface seriously hamper its application, and the underlying physics behind are still unclear. In this work, using in-situ environment scanning electron microscopy (ESEM), the morphological evolution of composite silicon-graphite electrodes with different ionic liquids as electrolytes are compared in the range of 20 °C–60 °C. Surprisingly, combining the microstructure and surface reaction products from transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS), it finds out that the fully reaction of lithium-silicon does not generate huge volume expansion, while the side reaction between graphite and electrolyte decomposition products causes dramatic volume expansion and hinders the further lithiation of silicon . On the other hand, the electrolyte which is capable of rapidly releasing F − to form LiF-rich solid electrolyte interphase (SEI) is favorable to maintain the structure integrity and cycling performance. This work casts new understanding from the perspective of intrinsic reaction between electrode and ionic liquid electrolyte, which suggests that the practical application of silicon-based electrodes with appropriate electrolyte is a promising route for high energy-density LIBs.
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