Study on Na⁺ Storage Mechanisms of Carbon Black (Supporting Information)

To better understand the Na⁺ storage mechanism of general carbon materials, the suitable choice of study model is really pivotal. Carbon black (CB) attracts us to consider that it is a suitable model to study the Na⁺ storage mechanism because CB is an extremely popular industry product, and a lot of organic groups exist on its surface. After detailed electrochemical evaluations, it is surprisingly observed that the CB shows the tremendous Na⁺ storage capacity. For instance, Na⁺ storage capacity is 103.3 mAh g⁻¹, after the discharge-charge process was performed 10000 cycles at 5.0 A g⁻¹. Additionally, the CB still shows the storage capacity at 90 mAh g⁻¹, during 10000 cycles at 10.0 A g⁻¹. The storage mechanism was studied from two aspects which are structural conversions and surface effect. After performing the XRD, XPS, BET measurements and DFT and GITT calculations, it is aware of that the synergistic effect of capacitive effect brought by the –C=O of ester groups on the CB surface and structural conversions of CB contribute to the Na⁺ storage capacity. Our analysis results about storage mechanism of CB are capable to provide a beneficial reference for unfolding the carbon materials having storage capacity for Na⁺.