基于酶解木质素的多孔炭负极制备与储锂性能

Fabrication of porous carbon materials derived from enzymatic hydrolysis lignin as anodes for lithium-ion batteries

生物质酶解木质素直接碳化后得到的硬炭通常具有低比表面积和孔隙不发达等特点,作为阳极应用于锂离子电池时容量低。为了提高储锂性能,将原料酶解木质素和活化剂氯化锌一步热处理制备多孔炭,通过调节氯化锌用量和活化温度制备出一系列具有大比表面积的多孔炭材料。利用X射线衍射、拉曼光谱、氮气吸脱附等温线及孔径分析、扫描电子显微镜等表征手段对热解碳化后最终产物多孔炭的晶相、石墨化程度、比表面积和孔径分布、形貌进行研究,同时对多孔炭材料的电化学性能进行评估。结果表明:在热解碳化温度700℃、酶解木质素与氯化锌的质量比为1∶3时,制备出的多孔炭材料电化学综合性能最优,表现出优越的倍率性能和循环稳定性。在电流密度50 mA/g时的放电比容量高达722 mAh/g,在电流密度1000 mA/g时的放电比容量为350 mAh/g;在电流密度100 mA/g时,经过100圈循环后电极容量保持率为74.7%。这种由低成本废弃物酶解木质素制备的多孔炭材料有望大规模应用于锂离子电池上,为废弃物酶解木质素增值化利用提供一个可行的途径。

The anode material of commercial lithium-ion batteries is mainly graphite,but its theoretical capacity is only 372 mAh/g,greatly limiting the improvement of energy density of lithium-ion batteries,which cannot meet the needs of electric vehicles and smart grid products in the future.Carbon materials obtained from the thermal conversion of renewable biomass have attracted extensive attention because of their unique structural characteristics,high specific capacity,and good cycle stability.Lignin is the second most abundant biomass material on the earth with an annual regeneration rate of 50 million tons and a carbon content of 50%.Industrial lignin can be obtained from various low-cost woody plants and even from industrial wastes,such as pulping black liquor(alkali lignin) and biorefinery residues(enzymatic lignin).Enzymatic hydrolysis of lignin has higher average molecular weight and fewer oxygen-containing functional groups because it is a nitrogen-containing source,and its structure is closer to the original lignin.Carbon materials with high nitrogen doping and graphitization can be obtained by direct pyrolysis of enzymatic hydrolysis of lignin.When being used in the anodes of lithium-ion batteries,its lithium storage kinetics and active sites increase,which can improve the lithium storage performance.However,the hard carbon synthesized by the direct carbonization of biomass enzymatic hydrolysis lignin usually has a low capacity due to its low specific surface area and underdeveloped pores when used as anodes for lithium-ion batteries.In order to improve the lithium storage performance,the porous carbon was synthesized by the one-step heat treatment of enzymatic hydrolysis lignin as precursors and the zinc chloride as an activating reagent.A series of porous carbon materials with large specific surface area were prepared by adjusting the amount of the zinc chloride and activation temperature.The resultant porous carbon materials after carbonization were studied by means of X-ray diffraction,Raman spectroscopy,N_(2) adsorption-desorption isotherm and pore size distribution analysis,and scanning electron microscopy.Additionally,the electrochemical performance of carbon materials was further evaluated.The results showed that when the mass ratio of enzymatic hydrolysis lignin to zinc chloride was 1∶3(w∶w) at 700 ℃,the obtained products exhibited the excellent rate performance and cycling stability.The carbon anodes delivered a reversible capacity of 722 mAh/g at a low current density of 50 mA/g and 350 mAh/g at a high current density of 1 000 mA/g.Moreover,the specific capacity retention was 74.7% after 100 cycles at 100 mA/g.Such porous carbon material from the low-cost waste enzymatic hydrolysis lignin is expected to be widely utilized as anodes in lithium-ion batteries.This work demonstrates a potential application for the value-added utilization of waste enzymatic hydrolysis lignin.