Biomass-derived Hard Carbon As Promising Anode Material For Secondary Batteries

Lithium-ion batteries?LIBs?,as one of the major energy storage systems,have been widely applied in portable devices.However,LIBs are difficulty to be a large-scale application owing to the finite source and uneven distribution of lithium element,so that we need to find a new alternative energy storage technology to reduce costs of LIBs.Based on the abundant sodium elements,sodium-ion batteries?SIBs?have drawn greater attentions.Although graphite is the most applied anode materials in LIBs?theoretical specific capacity 372 mAh g-1?,it has a small interlayer distance?0.335nm?for SIBs because the radius of sodium ion is 55% larger than that of lithium ion.Therefore,non-graphitizing carbons?hard carbons?are the important anode materials for SIBs.In addition,owing to its environmental friendliness and low cost,biomass-derived hard carbon has become a focus of concern for anode materials.In this work,we choose three different biomass materials?pistachio shells,sunflower seed shells and peanut shells?as raw materials and through two-steps method?low temperature hydrothermal treatment-high temperature pyrolysis treatment?to prepare biomass-derived hard carbons.Under different heat treatment temperatures?HTT?and hydrothermal treatment conditions,hard carbons show different properties of structure and morphology and exhibit different electrochemical performance for secondary batteries.Moreover,preparation of hard carbon-metal oxide material composites is efficient to improve performance of metal oxide materials,so that the application range of hard carbons is extended.Results of this paper are as follows:?1?In order to study the influence of heat treatment temperature?HTT?,we select pistachio shells and sunflower seed shells as raw materials to prepare biomass-derived hard carbons,and the reason shows that HTT affects the structural characterizations of hard carbons such as graphitization degree,defects amounts,specific surface and pore volume.By contrast,PSHC-1000 and CMF-1000 exhibit high reversible capacities,good cycling stabilities and rate performance.Moreover,we test the sodium-ion batteries with the stable NaNi0.5Mn0.5O2 as the positive electrode and PSHC-1000 as the negative electrode to demonstrate the actual performance of biomass-derived hard carbon.The full cell exhibits high reversible capacity and good cycling stability.In result,the choice of HTT is more important for electrochemical performance of hard carbons.?2?Based on the specific fiber structure of sunflower seed shells-derived carbon micro fibers,we extend the application range of hard carbons to prepare hard carbon-metal oxide material composites to improve performance of metal oxide materials.Herein,TiO₂ with stable structure and poor electrical conductivity has been used to prepare TiO₂/CMFs hybrids to improve the electrochemical performance of TiO₂.The good electrochemical properties of TiO₂/CMFs hybrids can be ascribed to the addition of CMFs,which can not only offer the efficient pathway for ion diffusion and electron transportation,but also provide an excellent contacting with the current collector.Therefore,we can use this method to improve the electrochemical performance of other metal oxide materials.?3?In hydrothermal treatment process,different conditions have an effect on structural and morphological characterizations of hard carbons.We choose NaOH solution concentrations and hydrothermal treatment time as variable to prepare peanut shells-derived hard carbon and serve as anode materials for LIBs/SIBs.By contrast,hard carbon under different hydrothermal treatment conditions expresses obvious differences in electrochemical performance for LIBs/SIBs.Therefore,through controlling the hydrothermal treatment conditions,structural and morphological characterizations of hard carbon can be regulated and electrochemical performance can be improved.In conclusion,biomass-derived hard carbon can not only show excellent electrochemical performance,but also improve the performance of metal oxide materials.Therefore,biomass-derived hard carbon can serve as promising anode materials for secondary batteries.