Preparation And Electrical Properties Of Rice Husk-based Porous Carbon Anode Materials

In recent years,in the face of the growing oil crisis and environmental pollution problems,people have begun to develop new types of efficient,pollution-free,sustainable development of clean energy and energy storage equipment.As an excellent energy storage device,lithium-ion batteries have been widely concerned by researchers because of their advantages of small size,high energy density,long cycle life and no memory effect.At present,lithium-ion batteries have been widely used in portable electronic products and new energy vehicles.As a traditional lithium-ion battery anode material,graphite has been diffusely utilized because it has the advantages of stable structure,outstanding conductivity and low voltage platform.However,graphite also has the disadvantages of low lithium insertion capacity and poor rate performance,which is difficult to meet the further development of high-power electronic products and new energy vehicles.Therefore,it is particularly important to study the anode materials of lithium-ion batteries that are safe,stable,high specific capacity and distinguished rateability.As a kind of agricultural waste,rice husks have not been used reasonably in production.If rice husks are investigated as raw materials to prepare carbon anode materials,not only can environmental pollution and production costs be reduced,but also the energy crisis can be effectively alleviated.Therefore,in this paper,rice hull cellulose-based lamellar porous carbon materials,rice hull cellulose-based hierarchically porous carbon materials and lamellar porous carbon materials that were doped with nitrogen and sulfur.We performed structural characterization and electrochemical performance analysis of these materials.The research contents and conclusions are as follows:?1?Using the rice husk to prepare lamellar porous carbon material.First,the rice husk is removed lignin with ethanol,dilute sulfuric acid is used to remove hemicellulose,the remaining part is carbonized at high temperature and SiO₂ is used as a hard template.2 M NaOH solution removes the SiO₂ and a lamellar porous carbon material is obtained.The calcination temperature and calcination time were used as variables to explore the effects of different calcination temperatures and calcination time on the structure and electrochemical performance of the material.The results show that the material?RH-LPC-700-1.5?,which is kept at 700?for 1.5 hours,has the best structure and electrical properties,mainly with a microporous structure and a specific surface area of up to 576 m² g^-1,with a discharge specific capacity of 1143 mAh g^-1 at 0.2 C.The discharge specific capacity is still 476.2 mAh g^-1 even at 5 C and the coulomb efficiency is close to 100%.?2?Using the rice husk to prepare hierarchical porous carbon materials.Similarly,the rice husk is removed the lignin with ethanol,dilute sulfuric acid is used to remove hemicellulose,the remaining part is then kept under hydrothermal conditions at 200?for a period of time to allow the cellulose to hydrolyze and SiO₂ to polymerize.After that,carbonization was performed at a high temperature and SiO₂ was used as a hard template.The SiO₂ was removed with a 2 M NaOH solution to finally obtain hierarchical porous carbon materials.The morphology of hierarchical porous carbons are affected by hydrothermal time,calcining time and calcining temperature.We compared hydrothermal time 0,12,24 and 36 h,calcining temperature 500,600 and 700?,calcining time 0.5,1.5 and 2.5 h.Finally,it was concluded that the material?RH-24HPC-600-1.5?with a uniform distribution of micropores,mesopores and macropores at a hydrothermal time of 24 h,calcination temperature of 600?and calcination time of 1.5 h.The specific surface area is 332 m² g^-1,the initial discharge specific capacity at 0.2 C is 1627 mAh g^-1 and the specific capacity after 100 cycles is 686.6 mAh g^-1.?3?In order to investigate the effect of nitrogen and sulfur doping on the structure and electrochemical performance of lamellar porous carbon materials,we added urea and thiourea to RH-LPC-600-1.5 and carbonized them at high temperature.The results show that nitrogen and sulfur can be uniformly doped into the material and the doping of urea makes the material thicker and the pore diameter becomes smaller.The incorporation of thiourea makes the pore size of the material uniform,which greatly increases the number of active sites and improves electrochemical performance.RH-LPC-NS has a specific surface area of up to 798.2 m² g^-1with a discharge specific capacity of 636.3 mAh g^-1 at a rate of 1 C and still has a discharge specific capacity of 284 mAh g^-1 at a rate of 10 C,which has tremendously improved the performance compared to RH-LPC-600-1.5.