| Lithium ion batteries（LIBs）as the most commonly used chemical energy and electrical energy conversion devices have been widely used in information technology,electric vehicles,aerospace and other fields.Due to their high energy density,long cycle life,small size,light weight,less memory effect,less pollution and so on,they have been considered to be one of the most effective ways to store electricity in the future.In order to meet the current market demand,the development of advanced electrode materials with higher capacity,longer cycle durability and better rate performance has attracted widespread attention.The traditional graphite electrode suffers from low energy and power density and low safety performance,which is difficult to meet the requirements of a new generation of electrical energy storage/conversion equipment.However,the porous carbon materials have advantages such as large specific surface area,uniform adjustable pore diameter,short diffusion path of ions and electrons and stable chemical properties.They have become one of the research hotspots in the field of electrochemical energy storage and have occupied an important position in the electrochemical fields related to energy storage and conversion,such as lithium ion batteries,super capacitors and fuel cells.In order to improve the energy density and rate performance of Li ion batteries,this paper aims to synthesize the porous carbon materials with lithium ion dissociation/intercalation energy storage function.Using mesophase pitch（MP）as carbon source,a series of mesophase pitch-based porous carbon materials were successfully prepared by SiO2 template method,CaCO3 template method and SiO2 template synergistic KOH activation method.The structure and morphology of the porous carbon materials were characterized by XRD,SEM,TEM,Raman,N2 adsorption/desorption and other methods.The prepared porous carbon materials were used as anode electrode materials for lithium-ion batteries.The electrochemical properties of porous carbon materials were tested and characterized by galvanostatic charge/discharge,rate test,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.The main results are as follows:（1）The mesophase pitch-based porous carbon materials have been successfully prepared using nano-SiO2 as template and MP as carbon source.The porous carbon samples have loose structure and good dispersibility.The pore diameter is concentrated at about 18 nm and the high-temperature heat treatment produces a hole expansion.The porous carbon materials with mesoporous,lamellar and graphitized microcrystalline structures perform well in terms of rate performance.The reversible capacity of the porous carbon sample synthesized with 10wt% SiO2 treated at 2400oC（A-10-2400）is maintained at 247.5 m Ah g-1 after 100 cycles at 1C current density.And it has a stable discharge capacity during the cycle.The layered porous structure and graphitized microcrystalline carbon domains contribute to shorten the diffusion distance and reduce the diffusion resistance,thereby promoting the rapid diffusion of electrolytes and Li+ in the material and improving the effective utilization of the material surface.（2）The mesophase pitch-based porous carbon materials have been successfully prepared using CaCO3 as template and MP as carbon source as well.With the increase of heat treatment temperature,the graphitization degree of the porous carbon sample increases and the pore size distribution becomes wider.The pore size is mainly mesopores centered at 15,35 and 50 nm,containing a small amount of macropores.The specific capacity firstly decreases and subsequently increases as the heat treatment temperature increases.The reversible capacity of the porous carbon sample synthesized with 60wt% CaCO3 treated at 900 oC（B-60-900）cycled 100 times at 0.1C current density is 374.2 m Ah g-1 and the capacity retention rate is 100%.With the increase of CaCO3 template content,the specific surface area and pore volume of porous carbon samples firstly increase and subsequently decrease.The specific surface area and pore volume of B-70-900 reaches the maximum,which are 112.33 m2 g-1 and 0.729 cm3 g-1,respectively.It shows a large first reversible specific capacity（428.4 m Ah g-1）.By changing the CaCO3 template content,the pore structure of the porous carbon material can be effectively adjusted to optimize its electrochemical performance.（3）The hierarchical porous carbon（HPC）materials with micropores and mesopores have been successfully prepared using SiO2 template in combination with KOH activation method.The content of micropores and mesopores can be effectively controlled by varying the mass ratio of SiO2/MP.With the increase of SiO2 content,the reaction activity of MP increased.The contents of micropores（1-2 nm）and mesopores（2-3 nm and 15-30 nm）are gradually increased.And the specific surface area and total pore volume can reach 909.31 m2 g-1 and 1.068 cm3 g-1,respectively.（4）When the HPC materials are used as anode electrode materials for a lithium ion battery,HPC materials exhibit high reversible capacity and excellent rate performance.Their layered structure and abundant microporous and mesoporous structures can serve as lithium storage active sites to increase lithium storage capacity and facilitate the rapid migration of lithium ions,thereby resulting in good electrochemical performances.With the increase of SiO2 content,the lithium storage capacity and rate performance of HPC firstly increase and subsequently decrease.The reversible capacity of the porous carbon sample synthesized with 30wt% SiO2 treated at 900 oC（HPC-30）cycled 100 times at 0.1C current density is 656.4 m Ah g-1.Through 1200 oC heat treatment,the cycling stability and the high rate capability of the HPC electrode are effectively improved. |
