Preparation Of Rice Husk-based Carbon And ZnO Composites And Their Lithium Storage Performance

Due to the world's concerns about environmental issues and the governmental corresponding encouragement policies,the transition from petrol-powered to electric vehicles has become a general trend.The prime technological requirement is to develop lithium-ion batteries(LIBs).Currently,graphite is widely used commercially as LIBs anodes because of its long cycle life,abundant material resources and low cost.However,it has a low energy density(372 mAh g-1),and there are also safety issues related to lithium deposition.In recent years,transition metal oxides have been widely studied due to their high theoretical specific capacity.The theoretical lithium storage capacity of ZnO(987mAh g-1)is nearly three times that of graphite.ZnO is completely non-toxic,its preparation process is simpler,and the lithium ion diffusion coefficient is also higher(10^-14to 10^-12cm²s^-1).However,lithium embrittlement leads to the electrochemically driven solid-state amorphization and pulverization of ZnO.Moreover,low electronic conductivity is also a critical problem limiting the application of the ZnO-based electrodes.Many previous efforts have focused on enhancing the conductivity and stability of the negative electrode material.An effective strategy is to combine ZnO with carbon.The introduction of carbon can not only improve conductivity,but also solve the problem of electrode disintegration caused by volume changes.Besides,using biomass as a carbon source is conducive to environmental protection and realizes waste utilization.The rice husk has a high amorphous silica content(the highest among the Gramineae plants),it can form a perfect template skeleton during the transformation of organic matter to hierarchical porous carbon.In this paper,rice husk in agricultural waste was selected as the carbon source and combined with ZnO in different morphologies as the anode material for LIBs.The microstructure characterization and electrochemical performance test of the composite material were carried out.The main research contents are as follows:(1)Rice husk was alkali-cooked to extract cellulose.Zinc chloride was used as a zinc source,then it was mixed with sodium hydroxide and subjected to hydrothermal reaction to obtain flower-like ZnO.The prepared rice husk cellulose and ZnO were subjected to a hydrothermal composite reaction,and carbon was uniformly coated on the flower-like ZnO surface to form a stable composite structure.We explored the effect of the hydrothermal time of ZnO and different material ratios of ZnO and carbon on the electrochemical performance.We also compared and analyzed the physical and electrochemical performance differences between pure ZnO and composite materials.The materials demonstrated a specific discharge capacity of 819.9 mAh g^-1after 100 cycles at a rate of 0.2 C.(2)ZnSO₄·6H₂O was zinc source.The NaOH solution was slowly dropped into the ZnSO₄·6H₂O solution under the vigorous stirring to obtain Zn(OH)₂.Then NH₄HCO₃powder as a buffer was added to obtain an ultrafine zinc oxide precursor.Then it was mixed with the prepared rice husk cellulose and subjected to a hydrothermal compound reaction to obtain a composite material.Compared with pure ZnO,the electrochemical performance of ZnO/rice husk carbon composite was greatly improved.The effect of different hydrothermal time on the electrochemical performance of composite materials was investigated.When the hydrothermal time was 24 h,the ZnO/rice husk carbon composite showed excellent electrochemical performance.The reversible specific capacity stabilized at 855.6 mAh g^-1after 200 cycles at 0.2 C.