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Developing a practical silicon-based (Si-based) anode is a precondition for high-performance lithium-ion batteries. However, the chemical reactivity of the Si renders it liable to be consumed, which must be completely understood for it to be used in practical battery systems. Here, a fresh and fundamental mechanism is proposed for the rapid failure of Si-based materials. Silicon can chemically react with lithium hexafluorophosphate (LiPF6) to constantly generate lithium hexafluorosilicate (Li2SiF6) aggregates during cycling. In addition, nanocarbon coated on silicon acts as a catalyst to accelerate such detrimental reactions. By taking advantage of the high strength and toughness of silicon carbide (SiC), a SiC layer is introduced between the inner silicon and outer carbon layers to inhibit the formation of Li2SiF6. The side reaction rate decreases significantly due to the increase in the activation energy of the reaction. Si@SiC@C maintains a specific capacity of 980 mAh g–1 at a current density of 1 A g–1 after 800 cycles with an initial Coulombic efficiency over 88.5%. This study will contribute to improved design of Si-based anode for high-performance Li-ion batteries.

Building a stable solid electrolyte interphase (SEI) is an effective method to enhance the performance of Si-based materials. However, the general strategy ignores the severe side reaction that originates from the penetration of the fluoride anion which influences the stability of the SEI. In this work, an analytical method is established to study the chemical reaction mechanism between the silicon and electrolyte by combining X-ray diffraction (XRD) with mass spectrometry (MS) technology. Additionally, a selective blocking layer coupling selectivity for the fluoride anion and a high conductivity is coated on the surface of silicon. With the protection of the selective blocking layer, the rate of the side reaction is decreased by 1700 times, and the corresponding SEI thickness is dwindled by 4 times. This work explores the mechanism of the intrinsic chemical reaction and provides future directions for improving Si-based anodes.

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