| dc.description.abstract | Utilizing silicon as an anode material in the rechargeable Li-ion batteries (LIBs) has received much attention during the past decades due to its superior theoretical capacity (3579 mAh/g for Li3.75Si or 4200 mAh/g for Li4.4Si), as well as its abundant natural resources, economic affordability, and safety. Nevertheless, Si undergoes severe volume expansion (300-400%) and mechanical vulnerability during lithiation/de-lithiation, causing fast capacity fading and poor cyclability. Then, stoichiometric silicon nitride (Si3N4) was taken into consideration since it has excellent mechanical properties (e.g., high strength, high hardness, and high fracture toughness) tolerating volume changes and mechanical pressure upon cycling. Based on the above properties, in this work, the structural, physical properties and electrochemical behavior of Si3N4 phases (α-Si3N4 and β-Si3N4) were compared to find the better phase, which was then combined with Si to produce the silicon nitride-based composite by the ball-milling method to establish a synergistic relationship. Furthermore, the exploitation of amorphous carbon protective coatings was approached, since carbon has small volume change during the electrochemical lithiation/de-lithiation processes and high electrical conductivity. As expected, the β-Si3N4 sample which obtained 92.7 mAh/g for the first reversible capacity, 32.4 % for the high-rate reversible capacity retention, was proved to be more efficient than the α-Si3N4 sample which attained 84.4 mAh/g and 30.6 %, for the first reversible capacity and high-rate reversible capacity retention, respectively. The β-Si3N4 sample with the amorphous carbon shell (β-Si3N4/C) exhibited 92.9 % of reversible capacity retention after 100 cycles at 50 mA/g and 7.4 x 10-14 of lithium diffusion coefficient (D-Li+), further demonstrating its potential capability. Subsequently, the β-Si3N4@Si composite and the β-Si3N4@Si composite with the amorphous carbon shell (β-Si3N4@Si/C) were successfully synthesized and evaluated. Moreover, the amorphous carbon-coated Si sample was also compared in this study. After 100 cycles at 500 mA/g, the β-Si3N4@Si/C composite showed the highest reversible capacity retention of 22.0 %, whereas for Si only 0.4 % initial capacity was retained. The β-Si3N4@Si/C composite also demonstrated its better high-rate performance with 14.1 % of capacity retention at 5000 mA/g and its much higher ion-diffusion acceleration with 9.4 x 10-14 of D-Li+. The enhanced cyclability and high-rate performance of silicon-based anodes owe to the high mechanical durability and excellent adhesive properties of β-Si3N4 along with the protective function of the amorphous carbon. | en_US |