Hard Carbon From Biomass As An Anode For Na-Ion Battery

The human society is facing with energy issue and environment pollution.Clean energy such as solar energy and wind energy is instability because of depending on natural conditions so closely.Therefore,there is an eager need for safe and reliable energy storage system applied to the practical application.Electrochemical energy storage has played a very important role for clean energy storage and utilization.The sodium ion batteries is one of the most promising application in the electrochemical energy storage technology,however,researching for an appropriate electrode material is the key to sodium ion battery.Hard carbon as the anode material for SIBs has been investigated by many researchers.In order to find high energy hard carbon materials for SIBs,during this work,we have chosen coconut endocarp as a precursor to systematically research the effects of carbonization temperature,carbonization time,activation treatment and acid rinse treatment on electrochemical performances.The main research contents and results are as follows:First of all,this work used biomass coconut endocarp as the precursor,and the hard carbon materials are prepared by carbonization,activation and acid washing treatment.Hard carbon materials are rich in disordered structure and amorphous construction by carbonization,and the carbonization temperature,carbonization time are important factors to affect the electrochemical performances;By potassium hydroxide solution activation,it is not only producing abundant pore structure,but also introducing a large number of functional groups on the surface of materials;Using hydrochloric acid to clean up impurities so that there are less heteroatoms in order to avoid the influence.Secondly,according to different experimental phenomenon,hard carbon materials with different treatments are investigated deeply,applying a variety of measurements to prove the relationship between different materials and electrochemical properties.Through those experiments,it can conclude that the best carbonization temperature is 1100oC for 2 h.With different comparison,result shows that biomass coconut endocarp without any treatment has revealed the highest specific capacity and performed more excellent electrochemical performances.It delivers initial charge capacity of 313.8 mAh g^-1 at 50 mA g^-1,high initial coulombic efficiency of 69.2%and superior cycle performance of 288.7 mAh g^-1 after 200cycles.At 500 mA g^-1,it also showed good cycle performance and the reversible capacity is 94 mAh g^-1.Those satisfactory electrochemical performances can be ascribed to both intrinsic stable structure and large layer space induced by heteroatoms.They are both beneficial to maintain original structure and expand layer spacing in order to promote sodium ions shuttle.On the contrary,the electrochemical properties of hard carbon materials treated by potassium hydroxide solution activation or hydrochloric acid treatment are worse than the untreated one.The study suggests that after being treated,the specific surface area increases,which would have an effect on the formation of SEI,and initial efficiency of the material decreases with the increase of the specific surface area.The more the treatment processes have,the worse the performance of the material is.In this work,material by potassium hydroxide solution activation of initial coulombic efficiency is 60.8%and initial charge capacity is 229.8 mAh g^-1.;otherwise,being treated with potassium hydroxide solution activation and hydrochloric acid treatment,it only has coulombic efficiency of 46.5%for the first cycle and initial charge capacity of 166.3 mAh g^-1.The advantages of hard carbon material such as high reversible capacity,low voltage platform,safe and reliable have made it as one of the most potential anode material for SIBs.However,the storage mechanism need to be further investigated and there still exist some problems in practical application.It is believed that hard carbon material will be put into practical use as continual investigation in hard carbon materials.