Ex-Situ Carbon Coating of LFP via Supercritical CO2-Assisted Surface Modification for Enhanced LIB Performance

LiFePO₄ (LFP) is a widely studied cathode material known for its elevated safety, cost-effectiveness, and stable long-cycle performance. Whereas, its practical application is hindered by challenges such as low electronic conductivity and insufficient capacity and rate performance. Herein, we propose a supercritical CO₂ (scCO₂)-assisted method to apply a low-cost, conductive polyacrylonitrile (PAN)-induced carbon coating on the LFP surface to resolve these issues. In this way, a 2 wt % PAN solution, calcined at 600 °C, forms a uniform N–C layer on the LFP particles. This modification leads to considerable improvements in both the electronic conductivity and the specific capacity of the materials. Electrochemical testing reveals that LFP/sc-PAN composite demonstrates an initial discharge capacity of 155.7 mAh g^–1 when tested at a rate of 1 C, retaining 83.13% of its capacity after 500 cycles, which outperforms both LFP/PAN and LFP. Additionally, LFP/sc-PAN shows stable rate performance across various discharge rates (0.2–10 C), with capacities of 165.1, 157.6, 155.7, 133.3, 110.1, 95.9, 85.1, and 75.8 mAh g^–1, all superior to LFP/PAN and LFP. These differences become more pronounced at greater rates, demonstrating the superior electrochemical performance of LFP/sc-PAN. These results indicate that the strategy of applying a uniform surface coating provides a scalable method for improving the performance of LFP and other cathode materials.