Preparation of Hard-Soft Carbon via Co-Carbonization for the Enhanced Plateau Capacity of Sodium-Ion Batteries

Hard carbons hold considerable promise as anode materials for sodium-ion batteries. Nevertheless, their inadequate closed pores are detrimental to the filling and extraction of Na⁺, which leads to poor plateau capacity during the charging and discharging processes and hinders the progress of application as high-energy carbon anodes essential for accelerating the commercialization of SIBs. In this work, we proposed a convenient co-carbonization strategy aimed at synthesizing hard-soft composite carbon materials featuring plenty of closed pores, which facilitates the storage of sodium ions and endows anodes with high-energy and reversible low-potential plateaus (<0.1 V). Furthermore, we systematically investigated the influence of closed pores on the electrochemical properties of hard-soft carbon. Specifically, the capacity in the plateau region of the hard-soft composite carbon (HC-SC7) reaches 200.2 mAh g^-1, with a 1.4-fold increase compared to unmodified resin-based hard carbon. In addition, HC-SC7 presents a capacity of 118.7 mAh g^-1 at 200 mA g^-1, marking a 2.3-fold enhancement over that of unmodified resin-based hard carbon. It is worth noting that HC-SC7 holds a capacity retention rate of 71% after 100 cycles at a current density of 50 mA g^-1, surpassing that of unmodified resin-based hard carbon by 18.6%. In summary, our research offers a straightforward approach to synthesizing high-energy carbon anode materials for sodium-ion batteries, which demonstrates the potential of sodium-ion batteries in practical applications and may promote their commercialization prospects.