Open Access

Due to the heavy overuse of fossil energy sources since the last couple of centuries, a range of serious concerns such as depletion of fossil fuels and climate change that is driven by extensive carbon dioxide (CO2) emission has risen. Rechargeable batteries have surged as eco-friendly and sustainable energy source alternative. Lithiumion batteries (LIBs) have been the most successful rechargeable battery since their commercialization. However, owing to exhaustion and instability in price of scarce raw materials, sodium-ion batteries (SIBs) have emerged as the most attractive alternative to LIBs. Nonetheless, there are still burdens to overcome for SIBs to achieve competitiveness over LIBs, particularly in improving their energy density. To address the burdens, diverse materials have been studied to date. Yet, progress and development on achieving high performance negative electrode for SIBs still remain as a key object. Hard carbon (HC) has been considered as attractive candidate, because of its high capacity and low production cost. Despite the attractiveness, inherent limitations of HCs such as excessive formation of solid-electrolyte interphase (SEI) and large irreversible capacity loss have hindered their applications. To confront this challenge, core-shell concept has been suggested by the team of Division 3.6 at BAM. The concept is to create carbon coating (shell structure) around the core material in order to mitigate formation of excessive SEI and enhance performance of the negative electrode. Shu-Han Wu and Paul Alexander Appel from Division 3.6 at BAM have synthesized various core-shell materials and have observed promising results. They made great progress in the research of core-shell materials, for example improving initial coulombic efficiency from 31% to 68%. However, there are still room for improvement. The task of this bachelor thesis work is to enhance the electrochemical performance of the core-shell materials and to investigate a more effective carbon coating method on the core material by exploring various coating parameters and different drying procedures. In this bachelor thesis, Shu-Han Wu’s synthesis precedure was repeated, ZIF-8 was pyrolyzed at 1000°C with a consequent treatment with HCl gas and washed with deionised water. The material (ZIF8_1000_HCl gas_H2O) was re-synthesized. Increasement in N2 Physisorption was observed after the acid treatment, consistent to Shu-Han Wu’s syntheis. The as-synthesized material was used as core material throughout this bachelor work. Moreover, 4 different core-shell carbon materials were synthesized by using chemical vapor deposition (CVD) and ball milling as synthesis methods. was used as core material and toluene was used as carbon precursor for CVD. CVD displayed an effective formation of shell structure evidenced by steep reduction in specific surface area (SSABET) from N2 physisorption characterization. Ball milling revealed to cause defects in shell structure, which was noticeable on increase in SSABET (from 14 to 379 m2 g-1) and pore size distribution characterization. Drying of powder material prior to CVD process did not exhibit a difference in porosity on the final product after CVD. From the galvanostatic cycling tests at a current density of 20 IVmA g⁻¹, it was evident that formation of shell structure enhances the performance of the material. Among the synthesized core-shell materials, the material double 1.5 h CVD with no ball milling in between exhibited the most excellent performance (ICE 60.1%). Powder drying prior to CVD showed a positive influence on improving the electrochemical performance (ICE improved from 45.1% to 51.9%). Increasing drying temperature of electrode resulted in increasements of performance, where the peak performance was reached at drying at 200°C (ICE 57.7%). The investigations of impacts of coating and drying on electrochemical properties of core-shell carbon materials would provide basis and motivation for further development of advanced negative electrode materials for SIBs.