| The exploitation of new generation of energy storage systems is very crucial for further utilizing clean energy efficiently.Sodium-ion batteries operating at room temperature have attracted gradually increased attentions in virtue of their outstanding electrochemical properties and low cost.The development of high-performance and low-cost anode materials is one of significant challenges for industrialization of sodium-ion batteries.In this paper,inexpensive walnut shell and glucose were selected as carbon source to prepare advanced sodium-ion battery anode materials.The relationship between microstructure,morphology of hard carbon and its electrochemical performance was comprehensively analyzed.The main research contents and results of this paper are as follows:?1?Walnut shell derived hard carbon materials were obtained by direct carbonization at 1100°C,and its micropore/mesoporous distribution was further modified by hydrothermal treatment.The results show that the hard carbon samples after hydrothermal treatment display fewer micropores and more mesopores than samples without hydrothermal treatment,and deliver better electrochemical performance.After 100 cycles at current density of 100 mA·g-1,a maximum specific capacity of 244.6 mAh·g-1 and first Coulombic efficiency of 64.0%is obtained.Furthermore,the storage mechanism of sodium ions in hard carbon was studied,and the effect of pore distribution on electrochemical performance was also analyzed.In all,we provided a effective strategy to optimize sodium storage performance of hard carbon anode by adjusting the nanopores distribution.?2?Using glucose as carbon source,we prepared a kind of monodispersed hard carbon microspheres through low-temperature hydrothermal treatment and followed high temperature carbonization at 1000-1200°C.Changing the NaCl concentration in hydrothermal solution could significantly regulate the diameter and microstructure of hard carbon microspheres.Within a certain range,the diameter increases along with the increase of NaCl concentration.The results show that when the NaCl concentration is 0.01 M and the carbonization temperature is 1200°C,the sample exhibits the highest sodium storage capacity of 327.1 mAh·g-1 after 200 cycles at 100mA·g-1,the first Coulombic efficiency is 81.3%.The reversible capacity at 500mA·g-1 is still above 250 mAh·g-1.When the concentration of NaCl is 0 M?deionized water is used?and the carbonization temperature is 1200°C,the sample shows superior electrochemical performance at high current density,the reversible capacity at 1000 mA·g-1 is still higher than 200 mAh·g-1.Hard carbon microspheres with a smaller size show greater advantages on rate performance.Moreover,the larger interlayer spacing and smaller graphite crystallite width in hard carbon is beneficial to sodium ions diffusing into the interlayer of graphite crystallitec resulting in better utilization of active sites.Therefore,the specific capacity is improved obviously.Using high specific surface area hard carbon as positive electrode,glucose derived hard carbon microsphere samples as negative electrode,sodium ion hybrid devices were assembled.The power/energy properties of hybrid devices are very excellent in virtue of the high rate performance and low potential capacity of glucose derived hard carbon microspheres.When the power density reaches around 6500 W·Kg-1,the energy density still remains around 100 Wh·Kg-1.In summary,we use inexpensive biomass precursors and a simple preparation method to synthesize high-performance sodium ion battery anode materials.The morphology and microstructure is proved has obvious effect on electrochemical properties of hard carbon,which provide referential value for sodium-ion batteries. |
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