Si@C Anode with Excellent Electrochemical Performance for Lithium-Ion Batteries: Microcapsules Composed of N-doped Carbon Shell and Diffusely Distributed Nano-Silicon Inside

As a promising candidate for the next generation of new anode materials, the modification and optimization of silica-based anode materials are significant. Using chitosan (CS) as the carbonaceous precursor, the N-containing Si@C microcapsules were prepared by emulsification cross-linking combined with high-temperature pyrolysis method. The microcapsule structure offers additional space for nano-Si and effectively enhances the electro-chemical properties of the anode. Moreover, optimizing the CS:Si ratio is advantageous in achieving a synergistic effect between silicon and carbon. When CS:Si = 4:1, the first specific capacity was 762.78 mAh/g and the retention rate was 69.27 % after 100 cycles. To further enhance the material properties, urea was added to a ratio of CS:Si = 4:1 as an N supplement for elemental doping modification. The specific capacity of the anode had a positive correlation with N content within a certain range. As the N content increases, the pyridine-N content and density of C vacancies also increase, which improves the storage form and diffusion path of Li+. When 0.75 g urea was added, the first reversible specific capacity reached 1108.88 mAh/g and the retention rate was 92.41 % after 100 cycles. This work offers environmentally friendly and safe methods, as well as a new modification concept for N-doped microsphere-encapsulated silicon-carbon composites.