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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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Silicon-based anodes are considered ideal candidate materials for nextgeneration lithium-ion batteries due to their high capacity. However, the low conductivity and large volume variations during cycling inevitably result in inferior cyclic stability. Herein, a dry method without binders is designed to fabricate Si-based electrodes with single-walled carbon nanotubes (SWCNTs) network and to explore the different mechanisms between SWCNT and multiwalled carbon nanotubes (MWCNTs) as a conductive network. As expected, higher initial discharge capacity (1785 mAh g −1 ), higher initial Coulombic efficiency (ICE, 81.52%) and outstanding cyclic stability are obtained from the SiO x @C|SWCNT anodes. Furthermore, its lithium-ion diffusion coefficient (D Li+ ) is 3-4 orders of magnitude higher than that of SiO x @C|MWCNT. The underlying mechanism is clarified by in situ Raman spectroscopy and theoretical analysis. It is found that the SWCNTs can maintain good contact with SiO x @C even under tensile stresses up to 6.2 GPa, while the MWCNTs lose electrical contact due to alternating compressive stress up to 8.9 GPa and tensile stress up to 2.5 GPa during long-term cycling. Under such very large stresses, the more flexible SWCNTs and their stronger van der Waals forces ensure that SiO x @C still has good contact with SWCNTs.

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Silicon-based anodes have been considered as ideal candidates for next-generation Li-ion batteries. However, the rapid cyclability decay due to significant volume expansion limits its commercialization. Besides, the instable interface further aggravates the degradation. Carbon coating is one effective way to improve the electrochemical performance.The coating integrity may be a critical index for core-shell structure electrode materials. Herein, the coating integrity of SiO x @C composite is tested by a developed selective alkali dissolution, further quantitatively depicted by a proposed index of alkali solubility 𝜶. The effect of coating integrity on electrochemical performance reveals that SiO x dissolution loss has a significant impact on the overall electrode structure stability and interface property. Because of the side reaction between uncoated active SiO x and electrolyte, the quadratic decrease of initial coulombic efficiency and increase of solid electrolyte interphase thickness with the rise of alkali solubility are closely related to the generated F content induced by active material loss, further supported by the obvious linear rise of Li 2 SiF 6 fraction, leads to the linear increase of interface impedance and volume expansion rate, which may take primarily responsibility for the performance decay. This work propels the fundamental understanding on the interface failure mechnism and inspires rational high-performance electrode material design.