An eggshell-structured N-doped silicon composite anode with high anti-pulverization and favorable electronic conductivity

Silicon is the most promising anode alternative for the next generation of lithium-ion batteries. However, the capacity of Si anodes quickly fades because of its large volume change during lithiation/delithiation, which heavily prevents its practical use. To alleviate this problem, herein, we design and prepare a microscale N-doped Si composite that has an eggshell structure. Mechanical milling of the sintered Si-xLiNH(2) mixtures under a CO2 atmosphere leads to the successful in situ creation of a similar to 10 nm thick amorphous Li2CO3 and SiOx shell containing well-dispersed Si3N4 nanocrystals on the surface of Si microparticles. The fine and dispersed Si3N4 nanocrystals significantly enhance the mechanical properties of the amorphous shell, providing it with remarkable hardness and toughness, consequently hindering the pulverization of the micro-Si particles during lithiation/delithiation. Moreover, doping with N improves the electrical conductivity of the Si composites, and the in situ-formed Li2CO3 contributes to a stable SEI layer on the electrode surface. Thus, the N-doped micro-Si composite with an eggshell structure demonstrates excellent electrochemical properties including a high initial reversible capacity (1820 mA h g(-1)), a reasonable cycle performance (1020 mA h g(-1) after 600 cycles), and a good rate capability (1117 mA h g(-1) at 2000 mA g(-1)).