In‐situ reconstruction of N‐doped carbon nanoflower coating layer for enhancing high pseudo‐capacitance in Bi‐based fast‐charging lithium‐ion batteries

Abstract As one of the alloy‐type lithium‐ion electrodes, Bi has outstanding application prospects for large volume capacity (3800 mAh·cm −3 ) and high electronic conductivity (1.4 × 10 7 S·m −1 ). However, the fast‐charging performance is hindered by significant volume expansion (> 218%) and a low rate of phase diffusion. To overcome these two problems, an N‐doped carbon nanoflower coating layer was elaborately in‐situ reconstructed on a multiple‐wall Bi microsphere by hydrothermal methods and subsequent calcination in this study. The carbon nanoflowers greatly increase specific surface area (40.0 m 2 ·g −1 ) and alleviate the volume expansion (130%). In addition, the incorporation of N‐doped carbon nanoflowers leads to a gradual enhancement in the Li adsorption energy of Bi during the process of lithium insertion and improves the electrical conductivity. Therefore, the contribution rate of pseudo‐capacitance reached 87.5% at the scan rate of 0.8 mV·s −1 , and the Li‐ion diffusion coefficient () was calculated in the range of 10 −10 to 10 −12 cm 2 ·s −1 . The Bi@CNFs anode provided a high specific volumetric capacity of 2117.0 mAh·cm −3 at 5C and a high capacity retention ratio of 93.2% after 800 cycles. The Bi@CNFs//LiFePO 4 full cell also displayed a stable capacity of 113.9 mAh·g −1 and energy density of 296.1 Wh·kg −1 after 100 cycles with a Coulombic efficiency of 97.6%. The mechanism of fast‐charging lithium storage was verified by distribution of relaxation time analysis and density functional theory calculation. This paper provides a new strategy to increase the pseudo‐capacitance and reduce the volume expansion for the preparation of alloy‐type fast‐charging electrodes.