Study On The Behavior Of Sodium Storage In Non-graphitized Carbon Materials

Energy storage and conversion technologies play an important role in the adjustment of energy structure and governance of environmental issues.Although lithium ion batteries(LIBs)have dominated the energy storage market due to their high energy density and excellent cycle stability,the relatively scarce and unevenly distributed lithium resources have raised concerns about the future development of LIBs.Therefore,it is very necessary to develop other cheap energy storage technologies that can replace LIBs.Considering the abundant reserves of sodium and its similar chemical properties to lithium,sodium-ion batteries(SIBs)have been considered as potential alternative for LIBs in the field of large-scale power grid energy storage.Developing and designing best-use electrode materials are the key for application of SIBs.Recently,although the cathode materials for SIBs have achieved great progress,the practical use of SIBs is still limited by the lacking of suitable anode materials.Among the various sodium storage anode materials,non-graphitized carbon materials(including soft carbon and hard carbon)are considered to hold the most promise to promote the industrialization of SIBs considering their advantages of low sodium storage platform,high sodium storage capacity and simple preparation process.However,there are still some key issues such as unclear sodium storage mechanism,low first-cycle coulomb efficiency,poor rate performance,unsatisfactory cycle stability and high cost,limiting the practicality of non-graphitizable carbon materials.Based on this,this paper focuses on the structural design and performance optimization of low-cost non-graphitized carbon materials.The obtained results are as follows:Low-cost leonardite humic acid(LHA)was adopted as the precursor to prepare high-yield hard carbon as anode for SIBs.The effect of carbonization temperature on the structure evolution of the obtained materials was investigated.The mechanism of sodium storage of hard carbon was explored by establishing the structure-activity relationship between its structural characteristics and sodium storage performance.It was found that the slope section in the charge-discharge curves of hard carbon is related to the adsorption of Na⁺at defects,while the plateau section is related to the intercalation reaction of Na⁺in the graphite-like crystallites.The obtained hard carbon material exhibits excellent sodium storage performance in terms of a high sodium storage capacity of 345mAhg^-1,a moderate initial coulombic efficiency of 73%and a good cycle stability.In order to further reduce the cost of hard carbon materials,agricultural productwaste apricot shells were used as the precursor to prepare hard carbons.The obtained hard carbon materials retain the natural pores and amorphous characteristics of the precursor,which not only shortens the sodium ion transmission distance,but also increases the active site for sodium storage,which significantly improves the sodium storage capacity and rate performance of the obtained samples.Subsequently,the structure of hard carbon was adjusted using high-temperature carbonization combined with H₂reduction to reduce defects,which significantly improve the initial coulomb efficiency of hard carbon and thus increase its reversible capacity.The hard carbon material obtained by this strategy exhibits excellent sodium storage performance with a sodium storage capacity of up to 398.8mAh g^-1,an improved first cycle coulombic efficiency of 76%and an enhanced rate performance.In addition,the full SIBs assembled based on this hard carbon also exhibit an excellent electrochemical performance with an energy density of 135Wh kg^-1and superior cycle stability.Based on the advantages of stable sources,low cost and high carbon yield of pitch materials,composite carbon materials with an amorphous structure was obtained by introducing hard carbon precursors into pitch from the perspective of inhibiting the ordering of pitch.The obtained samples exhibit excellent sodium storage performance with a reversible capacity up to 257.5mAh g^-1and excellent cycle stability.Based on this,porous carbon nanosheets were prepared by introducing Na Cl template,which further broke the graphitization behavior of pitch at high temperature.This not only enlarges the composite material layer spacing,but also introduces structural defects,increasing the sodium storage capacity of the composite carbon material to 302mAh g^-1and further improving its rate performance.A strategy combining nitrogen doping and pore control into one process was developed to prepare nitrogen-doped porous carbon.The obtained nitrogen-doped porous carbon was firstly evaluated as electrode materials for EDLCs.Then,from the perspective of optimizing the device to increase its energy density,sodium ion capacitors(NICs)were constructed based on the nitrogen-doped porous carbon as the positive electrode material and apricot shell-based porous carbon as the negative electrode material.The assembled NICs combine the advantages of SIBs and EDLCs,delivering a high power and energy output.The energy density of the assembled NICs can reach up to?180 Wh kg^-1even at a high power density of?1000 W kg^-1.In addition,the obtained NICs deliver an excellent cyclic stability and rate performance.This provides new ideas for the development of fast and efficient energy storage devices.