Nitrogen-Doped Hollow Carbon Spheres Based on Schiff Base Reaction as an Anode Material for High-Performance Lithium and Sodium Ion Batteries

Synthesis of multi-cavity mesoporous carbon nanospheres through solvent-induced self-assembly: Anode material for sodium-ion batteries with long-term cycle stability

Mesoporous carbon nanospheres (MCSs) are extensively employed in energy storage applications due to their ordered pore size, large specific surface area (SSA), and abundant active sites, resulting in excellent electrochemical performance for sodium storage. However, challenges persist in achieving precise structural control and stable synthesis reactions for these MCSs. Additionally, employing MCSs with a larger SSA in sodium storage applications can lead to increased side reactions and potential structural instability. To address these issues, we propose a solvent-induced self-assembly method for obtaining high nitrogen-containing multi-cavity MCSs with reduced SSA. The morphology and SSA of the nanospheres can be precisely adjusted by regulating the reaction time. Introducing an amine-phenol bridging structure into the polymer system significantly bolsters the structural and morphological stability of the mesoporous materials. The performance of these novel nanospheres in sodium-ion batteries (SIBs) is remarkable, exhibiting excellent sodium storage capability and exceptional ultra-long cycle stability. At a rate of 0.1 A g-1, the nanospheres achieved a high reversible capacity of 252 mAh g-1, and even after 20,000 cycles at 5 A g-1, a specific capacity of 136 mAh g-1 was retained. In summary, our study presents a novel approach for synthesizing mesoporous carbon materials and offers valuable insights for sodium storage research, opening new possibilities for enhancing energy storage applications.

High Proportion of Active Nitrogen-Doped Hard Carbon Based on Mannich Reaction as Anode Material for High-Performance Sodium-Ion Batteries

The potential for energy storage in carbonaceous materials is well known. Heteroatom doping - particularly nitrogen doping - can further enhance their electrochemical performance. The type of N configuration determines the reactivity of doped carbon. It remains a challenge, however, to achieve a high ratio of active N (N-5) in N-doped carbon. In this study, a high proportion of active nitrogen-doped hard carbon (PTA-Lys-800) is synthesized by the classical Mannich reaction, using tannic acid (TA) and amino acid as precursors. For sodium-ion batteries (SIBs), PTA-Lys-800 provides outstanding cycling stability and rate performance (338.8 mAh g^-1 at 100 mA g^-1 for 100 cycles, a capacity retention of 86 %; 131.1 mAh g^-1 at 4 A g^-1 after 5000 cycles). The excellent performance of PTA-Lys-800 is attributed to stable hierarchical pore structure, abundant defects, and a high proportion of N-5 formed during the carbonization process. Based on a detailed fundamental analysis, the pseudocapacitance mechanism is found to contribute to the higher sodium storage process in PTA-Lys-800. The Na-adsorption mechanism is further explored through ex situ Raman spectroscopy. A new method is presented for designing carbonaceous anode materials with high capacity and long cycle life.

Enhanced cycling stability and storage performance of Na0.67Ni0.33Mn0.67-xTixO1.9F0.1 cathode materials by Mn-rich shells and Ti doping

We propose a synergistic strategy of titanium doping and surface coating with a Mn-rich shell to modify the Na-rich manganese-oxide-based cathode material Na_0.67Ni_0.33Mn_0.67-xTi_xO_1.9F_0.1 in sodium-ion batteries and elucidate the underlying mechanism for enhanced material performance. First, it is found that the electrochemical performance of the proposed cathode material can be effectively improved when the Ti doping amount is x = 0.3. In addition to doping, the cathode material coated with a manganese-rich shell was prepared by a liquid coating method. The as-prepared Mn@Ti-doped-Na_0.67Ni_0.33Mn_0.37Ti_0.3O_1.9F_0.1 exhibited excellent electrochemical performance, delivering 169 mAh/g discharge capacity. The charge-discharge cycle test was carried out at a current density of 2C, and the sample not only provides a reversible capacity of 119 mAh/g but also has a capacity retention rate of 71 % after 500 charge-discharge cycles. The Ti doping and surface coating with a Mn-rich shell are shown to improve the specific discharge capacity, cycling stability and rate capability of the cathode material and mitigate voltage decay. These results validate our design principle and provide a novel approach to enhance the performance of cathode materials in sodium-ion batteries.