Characterisations and Electrochemical Performances of Hard Carbons in Sodium Ion Batteries
Carbons have been extensively studied in the literature as Na-Ion anodes: hard carbons, carbon black, carbon nanospheres, carbon fibers and graphene.
Carbon nanotubes made from polyaniline pyrolysis showed interesting performances. A reversible capacity of 250 mAh/g at a current density of 50 mA/g was obtained with 82% of capacity retention after 400 cycles. However the initial coulombic efficiency remains very low (around 50%) .
Ding et al.  tested carbon made from peat pyrolysis as anode for Na ion batteries. They obtained a reversible capacity of 255mAh/g after 200 cycles with a current density equal to 50 mA/g.
In our study, hard carbons (HC) were made from cellulose. Different final pyrolysis temperatures were studied from 700°C to 1600°C. Characterisation methods such as Small Angle X ray Scattering (SAXS) measurements; isotherms and Transmission Electron Microscopy (TEM) were performed in order to understand the impact of pyrolysis temperature on carbon structure. This parameter plays a major role on external and internal porosities. Different electrochemical tests were performed to study stability and rate capability of the samples. Figure 1 shows the cycling performances of the sample pyrolysed at 1400°C.
In our presentation, we propose to highlight the characterisations performed on these hard carbons. TEM images could clearly show the different graphene sheet arrangements. With the tests performed on Na//HC cells, we will try to correlate hard carbon structure to electrochemical performances. Perspectives on future studies will be also exhibited.
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