Insights into the Coating Integrity and its Effect on the Electrochemical Performance of Core–Shell Structure SiO_x@C Composite Anodes

Abstract

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.

Effective disproportionation of SiO induced by Na2CO3 and improved cycling stability via PDA-based carbon coating as anode materials for Li-ion batteries

“…S7,† the above two reduction peaks no longer appear in the following charging and discharge processes, which means that a stable SEI film is formed during the first cycle. 7,42 The above two reduction reactions are irreversible and consume Li ions in the electrolyte, increasing irreversible capacity loss. The potentials of lithium intercalation and the alloying reaction for d-SiO-G@C and d-SiO-G-5% materials are between 0 and 0.2 V. During the discharge process, there are three obvious reduction peaks for d-SiO-G@C, which are respectively at 0.04 V, 0.1 V, and 0.18 V. In the corresponding charging process, the oxidation potential appears at 0.11 V, 0.15 V, 0.24 V, and 0.44 V. Among them, 0.11 V, 0.15 V, and 0.24 V correspond to the delithium reaction of graphite, while 0.44 V corresponds to the oxidation reaction of Li x Si to Si.…”

Analysis of the Lithium Storage Mechanism in the SiOx/C Composite Based on the Performance Variation Applied to a Lithium-Ion Battery

“…On the basis of the first discharge specific capacity, the chemical composition of Li silicate can be calculated as Li 4.43 SiO 0.71 C 1.95 N 0.47 . In the first lithium intercalation process, a noticeable platform appears between 0.01 and 0.25 V, corresponding to the phase transition from SiO x C 4– x units and porous carbon to Li silicate and LiC 6 . , During the voltage range, the discharge specific capacity reaches 1348.9 mAh g –1 , accounting for 76.6% of the first discharge total quantity. Because the theoretical capacity of graphite is low (372 mAh g –1 ), SiO x C 4– x units contribute greatly to the capacity.…”

“…3,7 The broad reduction peak in the potential range of 0.01−0.30 V is attributed to the combined effect of Li silicate and LiC 6 formation from SiO x C 4−x units and carbon composite, while the broad oxidation peaks around 0.53−1.02 V describe the opposite conversion. 47,48 The difference in voltage range between the reduction and oxidation peaks may reflect different dynamic paths. 50 The enclosed area between the zero axis of the reaction current and the negative scanning curve is associated with the amount of free charge stored in the active material to some extent.…”

“…In the first negative scanning sweep, the reduction peak at 0.68 V indicates the formation of the SEI film, which disappears in the following cycles. Additionally, a subtle peak around 1.26 V results from the reduction of oxygen functional groups, and the oxidation peak at around 1.29 V corresponds to the reverse oxidation reaction. , The broad reduction peak in the potential range of 0.01–0.30 V is attributed to the combined effect of Li silicate and LiC 6 formation from SiO x C 4– x units and carbon composite, while the broad oxidation peaks around 0.53–1.02 V describe the opposite conversion. , The difference in voltage range between the reduction and oxidation peaks may reflect different dynamic paths . The enclosed area between the zero axis of the reaction current and the negative scanning curve is associated with the amount of free charge stored in the active material to some extent .…”

The acupuncture effect of carbon nanotubes induced by the volume expansion of silicon-based anodes

“…Our previous work revealed that the coating integrity is also important because of side reactions between uncoated active SiO x and the electrolyte. 26 In addition, the conductive network is also a key factor determining the stability and lifespan of Si-based anodes. [27][28][29][30] In practice, Si-based anodes usually contain conductive carbon, among which CNTs are the most commonly used.…”