(639a) Egg-Structural Si@Si3N4@C Anode with Admirable Cyclability, Rate Capability and Initial Coulumbic Efficiency

Si-based anode materials in lithium-ion batteries (LIB) suffered huge volume change during the charge-discharge cycling. Employing buffer materials to restrain its volume change was the key issue for these alloy-mechanism materials. Herein, we presented an innovative egg-structural Si-based compound: Si@Si₃N₄@C composite which was successfully prepared through a simple directly surface nitrified and chemical vapor deposition processes in a fix-bed reactor for the next generation high performance lithium ion batteries anode. The gas-solid contact reaction not only promised the uniformity of coating layers, but also was beneficial to the specific surface area control. The Nano-sized Si yolk displayed high capacity. The high strong and tough Si₃N₄ intermediate white as an effective structural buffer and Li⁺ conductive layer to accommodate the volume change as well as facilitate ion transport. The high-graphitized carbon shell enhanced integral conductivity, as well as stabilized SEI growth. Consequently, the egg-structural composite delivered a high 1^st discharge capacity of 3093.8 mAh/g with an initial coulumbic efficiency of 91.51 %, a exceeding 50 % capacity retention (vs 2^nd discharge) obtained after 100 cycles at 0.5 C. When at high current density of 10 A/g, an 881 mAh/g of capacity still displayed. When the current went back to 0.1 A/g, a high capacity recovery rate of 98.4 % regained, which shown the outstanding electrochemical reversibility of the egg-structural composite. Foremost, the influence of Si₃N₄ intermediate layer on Li⁺ diffusion was investigated firstly via the EIS measurements, after initial cycling, lithium ion solid diffusion coefficient (D_Li⁺) of egg-structural composite was 3.629×10^-10 cm²/s, 12.5 times higher than that of Si indicating an obvious promotion of Li⁺ diffusion. Moreover, during the cycling, the D_Li⁺ of egg-structural composite electrode was more stable and much higher than that of the Si and Si@C. The probable reason was discussed and proposed.