Gradient-coated P-doped Si3N4 with dual functions for silicon anodes: stress buffering and charge transport enhancement†

Abstract

To address the challenges of silicon anodes, including large volume changes and low ion mobility in Li-ion batteries, we propose a novel strategy: directly forming P-Si₃N₄ protective layers on Si particles. This coating mitigates structural degradation during cycling while enhancing electrical conductivity. Additionally, integrating pitch creates a conductive network, leveraging the high carrier concentration of P-Si₃N₄ for efficient electron transfer at high current densities. The N,P-Si@PC composite exhibits exceptional stability and capacity retention. Even after 800 cycles at current densities of 1 A g⁻¹ and 3 A g⁻¹, it maintains high capacities of 695 mAh g⁻¹ and 427 mAh g⁻¹, respectively. To elucidate the underlying mechanisms, we performed elasticity tensor analysis and Density Functional Theory (DFT) calculations. These studies reveal that P-Si₃N₄ enhances mechanical resilience, effectively reducing stress-induced fractures and limiting Solid Electrolyte Interphase (SEI) growth. Furthermore, DFT results indicate that phosphorus doping narrows the band gap, increasing carrier concentration and improving the conductivity of the protective layer. These alternative versions offer varied perspectives on addressing challenges with silicon-based Li-ion battery anodes through innovative coating strategies and theoretical insights into their mechanisms of action.