Design And Regulation Of Carbon Anode Materials And Study On The Lithium/Sodium Ion Storage Mechanism

Lithium-ion batteries（LIBs）have been widely used in daily life,and have been the focus of energy storage research and development.Meanwhile,sodium-ion battery（SIB）is considered to be an ideal supplement for lithium-ion battery owing to its abundant resources,low cost and similar working mechanism to lithium-ion battery.With the increasing global demand for energy storage in various fields such as electric vehicles and hybrid electric vehicles,higher energy density,faster charge/discharge rate and cycle performance are urgently needed.Graphite,as the anode material commonly used in LIBs,is limited by its structure.Therefore,it is urgent to find new anode materials to meet the requirements of high-power facilities.Among them,carbon materials are considered to be the most promising materials for commercialization at present due to the advantages such as non-toxic,harmless and low price.However,there are still kinetic issues such as low reversible capacity,poor conductivity,and rate performance.In this context,we have developed high capacity carbon anode materials for lithium/sodium ion batteries focusing on microstructure regulations and structure-activity relationship.The main research contents are as follows:（1）An efficient biomass utilization is proposed to prepare bio-oil-derived carbon（BODPC）with hierarchical pores and certain H/O/N functionalities for superior Li⁺/Na⁺storage,which with large surface area and pore volume,and coexistent micropores and mesopores.Micropores are favorable for large surface area and massive active sites,while mesopores facilitate the contact between the electrode and electrolyte to enable rapid ion diffusion.Promisingly,BODPC exhibits a high reversible specific capacity at 0.1 A g^-1(1881.7 m Ah g^-1 for Li⁺and 461.0 m Ah g^-1 for Na⁺),superior rate capability(674.1 m Ah g^-1 for Li⁺and 125.7 m Ah g^-1 for Na⁺at 5.0 A g^-1),and long-term cyclability.Kinetic analyses reveal that BODPC has similar behavior in the electrochemical Li⁺and Na⁺storage processes,in terms of physical adsorption（High potential region）,chemical redox reactions with surface functionalities（sloping region）,and insertion into the graphitic interlayer（low potential region）.（2）Heteroatom modification is one of the major areas to tuning the microstructure of carbon material toward improved electrochemical sodium storage.However,the reported doping method requires high temperature treatment,and the doping amount and chemical state of heteroatoms in carbon materials cannot be effectively regulated.Based on this,enhanced nitrogen（6.98 wt%）and sulfur（14.1 wt%）dual-doped carbon were synthesized via self-sacrifice template by using the precursor（sodium indigo disulfonate）as the source of N/S/C.Significantly,the N doping conduce to the conductivity and provide extrinsic defects,while the S atoms contributes to the enlarged interlayer distance to enhance the electrode kinetic.Meanwhile,S doping can offer extra active site in the form of C-S-S-C,which can be converted to C-S-Na,thus provide the fast surface pseudocapacitance contribution.As a result,the obtained co-doped carbon exhibits an extraordinary excellent rate capability(114.1 m Ah g^-1 at 10 A g^-1),and long-term cycling stability with 176.7 m Ah g^-1 at 2.5 A g^-1 after 3000 cycles for Na-ion storage.（3）The above N/S co-doped carbon materials exhibited low ICE,and designing doped carbon with excellent rate performance and high initial Coulombic efficiency（ICE）is critical for practical application of sodium-ion batteries.In order to further improve the rate performance,N/S co-doped porous interlaced carbon nanofibers were synthesized by using graphite as conductive matrix and sodium indigo disulfonic acid as template and carbon source.N/S-PICFs showed that the high ICE of about 70%and the excellent rate performance of(214.9 m Ah g^-1 at 10 A g^-1),and the capacity retention is above 80%after 1500 cycles.High N and S co-doping,interconnecting mesoporous structure,and the introduction of graphite nanosheets enable the formation of a good conductive network to ensure fast electron/ion transport.Kinetic analysis indicates that the material exhibits high surface-dominated sodium ion storage behavior.