Wangui Chen,Weitong Pan,Lili Zhao,Longfei Tang,Lu Ding,Xueli Chen,Fuchen Wang
Low specific surface area (SSA) in hard carbon anodes is crucial for enhancing the initial Coulombic efficiency (ICE) and reversible capacity of sodium-ion batteries (SIBs). Conventional strategies for SSA reduction within high-temperature carbonization processes often rely on additional energy-intensive thermal treatments or complex processes, presenting significant barriers to practical application. This study introduces a simplified and effective approach that operates within a standard high-temperature framework (1300 °C) by solely controlling the packing thickness of coconut shell char (CSC) precursors. Increased packing thickness induces diffusional resistance, hindering volatile release and achieving a volatile release reduction of 7.68 %. This confinement effect promotes in-situ secondary cleavage of volatiles, accelerating carbon deposition and reducing surface defects. Consequently, SSA decreases significantly by 71.52 %, while closed pore formation is enhanced. The optimized CSC-HPT-1300 exhibits dramatically improved electrochemical performance over the low-packing-thickness control, achieving a 15.48 % higher ICE (85 %), a 15.39 % increase in reversible capacity (280 mAh g −1 ), and a 25.90 % enhanced plateau capacity (209 mAh g −1 ). Furthermore, this strategy concurrently increases carbonization mass yield by 4.64 %. This thickness-controlled carbonization presents a straightforward and scalable optimization to standard high-temperature processing for fabricating low-surface-area hard carbons, advancing sustainable SIBs development.
SAPO-11 molecular sieves with different crystal sizes and particle sizes, especially nanosized small-crystal SAPO-11 molecular sieves, were successfully synthesized, and the corresponding NiWS-supported catalysts were prepared for the hydroisomerization of n-hexadecane. XRD, SEM, N2 adsorption–desorption, Py-IR, and HRTEM were used to analyze the effects of crystal size and particle size of the supports on their physicochemical properties, active phase properties, and catalytic performance of the catalysts. Through reaction evaluation and analysis of isomeric products, the effects of the size change of the support on the hydroisomerization performance of the catalyst and the hydroisomerization depth of n-hexadecane were determined. Through comprehensive analysis of the cracking products, it was determined that secondary cracking occurred when the conversion of n-hexadecane on the NiW/SAPO-11-S catalyst reached about 42.7%, and the secondary isomerization occurred when the conversion of n-hexadecane reached about 80%. The hydroisomerization reaction network of n-hexadecane over the NiWS/SAPO-11 catalyst was studied emphatically, and it was found for the first time that the secondary cracking of n-hexadecane during hydroisomerization followed the C3-β-scission mechanism.
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