Preparation And Electrochemical Performance Of Rice Husk-based Porous Carbon Anode Material

The lithium-ion battery is one of the most widely used energy storage systems in computers,electronic devices and electric vehicles,which is beneficial to meet the increasing demands of renewable energy and solve the climate-change issues caused by the combustion of fossil fuel and the emission of relevant greenhouse gases.Graphite is the most comment used anode material for lithium-ion batteries,however,its low theoretical specific capacity(372 m Ah g^-1)is unable to meet the needs of development.Rice husk,an agricultural waste containing amounts of carbon sources,represents one of the best choices for the carbon anode materials,which can not only prepare a new biomass carbon material but also avoid the impact on the environment by burning the wasted rice husks.Hence,in this paper,we use the rice husk to prepare the porous carbon materials and perform the measurement of morphological characterization and electrochemical performance to investigate its properties.The main results and conclusions are as follows:（1）The preparation of rice-husk-based porous carbon material.Firstly,the rice husk is carbonized to obtain the composite of SiO₂/C,then mix it with the K₂CO₃ activator to the grinder and put the mixture to tube furnace for calcining.The rice-husk-based porous carbon material is obtained by cooling the sample to room temperature and rinsing until neutral.To compare the obtained materials by direct activation（one-step method）,we adopt NaOH to remove the SiO₂ for obtaining the carbon template and activate the samples based on the experiment procedure（two-steps method）in order to compare the impact of different methods on the performance of materials.Moreover,we also investigate the influence of different ratios of activator on the structures and performances.The results demonstrate that samples reach the best performance with 900℃and 1h calcination temperature and time,one step method experiment,and the 3:1 mass ratio between the activator and SiO₂/C composite,which maintain the cross-sect porous structures and 551.4m Ah g^-1 specific charging capacity after 100 cycles at 0.2 C rate.（2）The preparation of lignin-based porous carbon material.We used a simple method via extracting the lignin from rice husk by ethyl alcohol,in which the lignin is dissolved in ethyl alcohol.As lignin cannot be dissolved in water,we add water into ethyl alcohol to separate lignin and perform suction filtration and drying to obtain rice-husk lignin.Then mix it with the K₂CO₃ activator to the grinder and put the mixture to tube furnace for calcining under Ar atmosphere.The rice-husk-lignin-based porous carbon material is obtained by cooling the sample to room temperature and rinsing until neutral.We have investigated the effect of different ratios of activator and different calcination times.The results indicate that the best performance of samples is obtained with 900℃and 1h calcination temperature and time,and the 3:1 mass ratio between the activator and the lignin,which form the continuous distribution of micropore-mesoporous structure and reach 610.1 m Ah g^-1 specific charging capacity after 100 cycles at 0.2 C rate.（3）The preparation of rice-husked porous carbon material with N-and S-doping elements.We mixed the prepared rice-husked porous carbon material with the urea and thiourea in the mass ratio of 1:8,then adding water and stirring for 24 h.The samples after drying were put into the tube furnace to calcine for 1.5 h under Ar atmosphere at 600℃,and the porous carbon material with N-and S-doped elements can be obtained after cooling to room temperature.Relatively,the N-and S-doped porous carbon material possesses the best performance,which takes advantage of the synergetic effects of N and S elements to enhance the electronic performance of materials and provides more active sites for the intercalation of Li-ions.The final homogenous porous structure also leads to the improvement of electrochemical performance,which maintains 450.3 m Ah g^-1 specific charging capacity after 100 cycles at 0.2 C rate.