Application Of Rice Husk For Supercapacitors And Lithium-Ion Batteries

Rice husk,as a natural and abundant biomass,contains abundant carbon elements and a large amount of silica.Carbon and silicon materials can be prepared from rice husk and are widely applied in supercapacitors and lithium-ion batteries areas.In this paper,we employ rice husks as raw material and mainly study two parts.Firstly,rice-husk-derived porous carbons are prepared from rice husks without any pretreat by one-step activation with CuCl₂,and study its electrochemical performance in supercapacitors.Secondly,rice-husk-based silicon materials are prepared from rice husks by magnesiothermic reduction method.And study the effect of adding NaCl during magnesiothermic reduction process on performance of lithium-ion batteries.The main contents are summaried as follows:1.Rice-husk-derived porous carbons are prepared directly from rice husk by employing CuCl₂ as activator through one-step method.By adjusting the dosage of CuCl₂,we have prepared a series of porous carbon materials with different porosity.The electrochemical performances are investigated by galvanostatic charge-discharge?GCD?,cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?methods.When the mass ratio of activator to rice husk is 7?25?1,the porous carbon material?RHPC-7?possesses largest specific surface area(1786.57 m²·g^-1)and highest pore volume(0.8854 cm³·g^-1).When used as supercapacitor electrode materials,RHPC-7exhibits highest specific capacitance,excellent rate performance and good cycle stability.A high specific capacitance of RHPC-7 is 174.89 F·g^-1 in 6.0 M KOH electrolyte at scan rate of 2 mV·s^-1 and a high specific capacitance sustains 101.31 F·g^-1 when scan rate increased to 100 mV·s^-1,suggests that RHPC-7 own high specific capacitance and good rate capability.Besides,RHPC-7 displays outstanding cycling performance with a specific capacitance of 157.68 F·g^-1 after 10000 cycles at current density of 1.0 A·g^-1,with a specific capacitance retention rate about 94%,.Before 10000cycling,the ESR and R_ct of RHPC-7 is 0.7949?and 1.52?;after GCD cycling,they are changed to 0.4030?and 1.573?.The decreased ESR of RHPC-7 electrode can be attributed to the activation of electrode materials and the full in filtration of electrolyte into electrode materials,but the change value of R_ct is very small,which further suggests that RHPC-7 shows good cyclic stability.In addition,activation agent,CuCl₂ is reusable and can be recycled a high recovery rate of 80%.Besides yielding porous carbon with outstanding performance,this method is highly cost-efficient,eliminates pollution and prohibits corrosion for equipments.Furthermore,this green strategy can judiciously be adopted to prepare other porous carbon materials from different biomass which can be applied to several novel applications.2.Silica is obtained by burning rice husk without any pretreatment in air and then prepared silicon by magnesium thermal reduction method.Study the effect of adding heat-scavenging NaCl in the magnesiothermic reduction process on the performance of lithium ion batteries.The experimental result suggests that RH-Si-NaCl possesses smaller pore size,larger specific surface area and higher porosity.Higher specific surface area and porosity facilitated the lithium ions'transportation,while smaller particle size of RH-Si-NaCl shorten the diffusion path of Li⁺.When used as anode material for lithium ion batteries,RH-Si-NaCl exhibits better electrochemical performance,the specific capacity of RH-Si-NaCl is 876 mA·h·g^-1 at current density of0.1 C and sustains high specific capacity of 632 mA·h·g^-1 at current density of 2 C.And the specific capacity at 2 C is about 72%of specific capacitance at current density of0.1C.The specific capacity is 584 mA·h·g^-1 after 100 cycles at current density of 0.1 C.While the specific capacity of without adding NaCl?RH-Si?is 685 mA·h·g^-1 at 0.1 C,the specific capacity at 2 C is only 36%of specific capacitance at current density of0.1C.The reversible specific capacity after 100 cycles is only 211 mA·h·g^-1 at 0.1 C and is about 0.36 times of RH-Si-NaCl after 100 cycles.The electrochemical impedance spectroscopy is used to verify that the addition of NaCl can improve the lithium ion diffusion coefficient,enhance the conductivity of the material,and make the material form a more stable SEI film during the first charge-discharge process.Thus,RH-Si-NaCl exhibits better rate performance and cycle stability.