Synergistic effect of P-dopant and N-doped carbon encapsulation on ball-milled silicon nanoparticles improved Li⁺ diffusivity in silicon anode by tenfold. While N-doped carbon encapsulation mainly improves Li⁺ diffusivity, P-dopant increases the internal conductivity and further enhances Li⁺ diffusivity, stabilizing the cell performance at high current densities. The anode achieves 87.32 % capacity retention after 400 cycles at 4000 mA g⁻¹.

Abstract

The silicon (Si) offers enormous theoretical capacity as a lithium-ion battery (LIB) anode. However, the low charge mobility in Si particles hinders its application for high current loading. In this study, ball-milled phosphorus-doped Si nanoparticles encapsulated with nitrogen-doped carbon (P−Si@N−C) are employed as an anode for LIBs. P-doped Si nanoparticles are first obtained via ball-milling and calcination of Si with phosphoric acid. N-doped carbon encapsulation is then introduced via carbonization of the surfactant-assisted polymerization of pyrrole monomer on P-doped Si. While P dopant is required to support the stability at high current density, the encapsulation of Si particles with N-doped carbon is influential in enhancing the overall Li⁺ diffusivity of the Si anode. The combined approaches improve the anode's Li⁺ diffusivity up to tenfold compared to the untreated anode. It leads to exceptional anode stability at a high current, retaining 87 % of its initial capacity under a large current rate of 4000 mA g⁻¹. The full-cell comprising P−Si@N−C anode and LiFePO₄ cathode demonstrates 94 % capacity retention of its initial capacity after 100 cycles at 1 C. This study explores the effective strategies to improve Li⁺ diffusivity for high-rate Si-based anode.