Microporous Carbon Nanospheres with Fast Sodium Storage Capability Enabled by Dominant Capacitive Behavior

Hard carbon is considered one of the most promising anode candidates for sodium ion batteries but suffers from a moderate rate performance. Here, we design microporous carbon nanospheres using a novel hybrid monomer that simultaneously involves an organic moiety and an inorganic moiety as the starting unit. The inorganic moiety forms a continuous network, which serves as a 3D scaffold and a nanometer-scale template, then supports the off-collapse of the carbon skeleton and creates a well-developed microporous structure. In addition, the graphite microcrystal structure can be tailored by adjusting the heating treatment temperatures. The electrochemical study demonstrates that the microporous carbon nanospheres show dominant capacitive sodium storage behavior, thus presenting an outstanding rate performance. Even if a very high current density of 10 A g^-1 is applied, the hard carbon anode can deliver a large capacity of 127 mAh g^-1 with a considerable plateau capacity of 53 mAh g^-1, which has rarely been obtained in previous publications. Besides, the carbon anode has a good cycling stability, and the capacity reached 210 mAh g^-1 after 1000 cycles with a current density of 1 A g^-1, showing no dramatic capacity loss.