Preparation Of Hard Carbon Negative Electrode Materials And Applications In Supercapacitors And Sodium-ion Batteries

There are two main categories of electrochemical energy storage devices: supercapacitors and batteries.Supercapacitors have many advantages in portable electric equipment and new energy buses because of their good high-power charging and discharging performance.However,th e lower energy density limits its further development.As a device with higher energy density in electrochemical energy storage,batteries have also attracted the attention of scientific researchers.In recent years,sodium ion batteries are considered to be a new type of secondary battery suitable for large-scale energy storage,and sodium resources are more abundant than lithium resources,and the development of sodium ion batteries is a current research hotspot.Battery electrode materials are developing in the direction of supercapacitor-type high-rate characteristics,and thus it is hoped that the problem of low power density of batteries could be solved.Hard carbon materials can be used as anode materials for supercapacitors and sodium ion batteries and the energy storage behavior of the same material in two devices are studied in this thesis,The characteristics of the energy storage type are displayed.It is helpful for different devices to make up for the shortcomings and realize the balanced development of device performance.For this reason,the starting point of this thesis is to investigate the energy storage types of hard carbon materials,which are used for supercapacitors and sodium ion batteries.The main contents should be included as the followings:(i)Biomass tamarisk tree branch derived carbon materials are used in supercapacitors and sodium ion batteries.The tamarisk tree branch is modified with an alkali activator,and the best modified ratio capacitance is obtained through electrochemical testing.The prepared carbon is applied to supercapacitors with a specific capacitance of 406 F/g,and applied to sodium ion batteries with 235 m Ah/g specific capacity.And the relationship between structure and performance is systematically studied using different calculation methods to quantify the capacitance contribution of electrode materials.The results show that the specific surface area of the el ectrode material is positively correlated with electrochemical performance when applied to supercapacitors,and the specific surface area is negatively correlated with the first discharging efficiency when being applied to sodium ion batteries.The calculation results show that the high-capacitance carbon material has been successfully prepared.(ii)Carbon materials derived from waste biomass of lemon peel are also applied in supercapacitors and sodium ion batteries.The lemon peel is modified with alkali activator,and the relationship between specific surface area,pore size distribution and morphology and other factors and performance are studied.The carbon is applied to supercapacitors with a specific capacitance of 448 F/g,and applied to sodium ion b attery with a specific capacity of 195 m Ah/g.Different methods are used for caculating the types of supercapacitors and sodium ion batteries.It is concluded that when both are calculated using Dunn’s formula,the "EDLC contribution" in the supercapacitor and the "capacitance contribution" in the sodium ion battery are conceptually consistent.Although the electrode materials have similar energy storage types in the two applications,there are differences in energy storage ions,electrolyte systems,and SE I membranes.(iii)Polymer Phenol-formaldehyde resin derived carbon materials are used in sodium ion batteries.The alcohol activation method is used to modify the Phenol-formaldehyde resin during the synthesis process,and the relationships between the specific surface area,morphology,etc.and electrochemical performance are studied.The results show that the longer the carbon chain,the more obvious the increase in the specific surface area of the phenolic resin.The carbon microsphere electrode materia l with platform capacity as the main material is prepared,and the specific capacity is 308 m Ah/g.The Dunn formula and the GCD method are used to calculate the proportion of the energy storage type of the electrode material.The Dunn formula is no longer suitable for electrode materials with obvious discharge platform capacity,and the GCD method still has certain practical comparative significance.