Preparation And Sodium Storage Properties Of Enzymatic Hydrolysis Lignin Derived Hard Carbon And Its Composites

As a new type of energy storage battery,sodium-ion batteries（SIBs）have wide application for large-scale energy storage.Biomass-derived hard carbon owing to abundant resource and low cost is regarded as the most promising anode material for SIBs.Lignin-derived hard carbon is a kind of non-graphitic carbonaceous material with disordered carbon structure and large interlayer spacing（0.36～0.4 nm）,which exhibits high specific capacity(250～400 mAh g^-1)for sodium-ion batteries.The enzymatic hydrolysis lignin contains nitrogen,and its structure is closer to the original lignin.Nitrogen-doped hard carbon with high graphitization can be obtained by utilizing pure enzymatic hydrolysis lignin as precursor,but presenting poor rate performance and cycling stability.In order to solve these problems,nitrogen-doped carbon,carbon composites and tin-carbon composites were prepared based on the pyrolysis of enzymatic hydrolysis lignin to realize high-performance energy storage for sodium-ion batteries.The main research content is as follows:（1）Hard carbon anode material with high nitrogen content is obtained by using enzymatic hydrolysis lignin as precursor and urea as nitrogen dopant.The introduction of nitrogen atoms accelerates electron migration and expands the interlayer spacing of hard carbon,realizing rapid Na⁺（de）intercalation inside hard carbon anodes.The as-prepared carbon material with nitrogen content of 5.26 wt%has a superior rate capability and ultra-long cycling performance,delivering a discharge capacity of 231 and 53 mAh g^-1 at 20 and 1000 mA g^-1,respectively,and a high capacity retention of 82%at 100 mA g^-1 after 200 cycles.（2）High-performance nitrogen-doped carbon composites are prepared via the pyrolysis of enzymatic hydrolysis lignin and Prussian blue.Prussian blue as a nitrogen dopant produces another highly graphitized carbon with the assistance of catalyst metal Fe derived from Prussian blue during pyrolysis process.Prussian blue-derived carbon is uniformly dispersed on enzymatic hydrolysis lignin-derived hard carbon,which improves electrical conductivity of the carbon composites.The as-prepared carbon composites with large interlayer spacing（0.392 nm）and high nitrogen content（6.74 wt%）exhibit excellent sodium storage performance in view of high discharge capacity of 293 mAh g^-1 at 20 mA g^-1 and capacity retention of 98%at 100 mA g^-1 after200 cycles.（3）High-performance Sn/C hybrids are prepared by a two-step method,combining hydrothermal treatment with high temperature pyrolysis treatment.Carbon derived from low-cost enzymatic hydrolysis lignin serves as a robust support for uniform Sn particles dispersion.Enzymatic hydrolysis lignin-derived hard carbon not only relieves Sn volume expansion and mechanical stress concentration,but also offers extra active sites and facilitates electron transfer.The resultant Sn/C electrode exhibits a discharge capacity of 131 mAh g^-1 at 1000 mA g^-1,and capacity retention rate of 91%after 1000 cycles at 1000 mA g^-1.