Onion-like Synergetic Multilayer Coating for High-Stability Silicon Monoxide Anode in Lithium-Ion Batteries

Abstract

Silicon monoxide (SiO) is a potential next-generation high-capacity anode material for lithium-ion batteries. However, SiO undergoes severe volume change during charge and discharge, which leads to mechanical failure and thus fast capacity decay. Nano-structuring has been reported as an effective method to improve cycle stability of SiO by preventing particle pulverization and increasing void content to accommodate the large volume change. Though, nano-particles are difficult to handle and energy-intensive to manufacture in large scale. In addition, the larger surface area facilitates side reactions between active material and electrolyte. Therefore, the use of micron-size materials is desirable. Herein, we engineer a multilayer surface coating on micron-sized (5 µm) carbon-coated SiO particles (SiO@C) to enhance the stability of the electrode during charge and discharge. The layer of carbon on SiO@C enhances its electrical conductivity. The material is treated with ultra-violet irradiation to generate -OH functional groups on its surface. The resulting particles are treated with an organosilane self-assembled monolayer (SAM) with (3-aminopropyl)triethoxysilane (APTES). The powder is then further combined with imide monomers and heat-treated to form a robust chemical bonding between the amine (-NH2) functional group of the SAM and the dianhydride group of the polyimide (PI) on the surface. The resulting SiO@C@UV@NH2@PI composite possesses excellent mechanical stability, where the high-modulus PI layer suppresses volume change, particle pulverization and electrode cracking during charge and discharge. In addition, the PI coating reduces side reactions between the electrolyte and the active material and improves the Coulombic efficiency of the electrode. Our study demonstrates that the SiO@C electrode with the multilayer coating exhibits a stable capacity of 1310.7 mAh g-1 after 100 cycles at 150 mA g-1, and a capacity of 910.3 mAh g-1 (capacity retention 94.2%, with respect to the 2nd cycle) under 1 A g-1 after 300 cycles. In comparison, SiO@C electrode without surface coating gives only a reversible capacity of 247.1 mAh g-1 after 100 cycles, with a 15.1% capacity retention (see Figure 1a). Figure 1b shows a comparison of the thickness change of the two SiO electrodes during charge-discharge, verifying that the multilayer coating can reduce volume expansion. Further characterizations of the surface-coated material to identify the mechanism of the improvement are underway and more data will be presented at the meeting. Figure 1