High-Speed Lithium-Ion Transfer inside Mesoporous Core-Shell LiFePO₄/Carbon-Sphere Cathodes

A thin layer of LiFePO₄ was coated onto a mesoporous carbon sphere to obtain a mesoporous core-shell LiFePO₄/carbon sphere (LFP/MCS) composite, for which the thickness of the nanoscale LiFePO₄ thin shell was approximately 30-50nm. Meanwhile, pristine LFP and MCS mixed with LFP samples (MCS-m-LFP) were prepared for comparison. The significantly larger surface area of LFP/MCS (43-151m²g^-1) compared with pristine LFP (12m²g^-1) is derived from the mesoporous carbon framework and thin nanoscale LFP shell. The large surface area of LFP/MCS provides greater surface content between the LiFePO₄ shell and electrolytes, which results in a high charge-discharge rate. Also, this remarkably thin LiFePO₄ cathode shell shortens the diffusion length of lithium ions thereby achieving a high charge-discharge rate for electrode materials. Consequently, under all charge-discharge rates (0.1-20C), the specific capacities of LFP/MCS are higher than those of both the pristine LFP and MCS-m-LFP. More specifically, at 10C, LFP/MCS exhibited the excellent rate performance of 82mAhg^-1, compared to 25 and 41mAhg^-1 for LFP and MCS-m-LFP, respectively. Furthermore, the discharge capacity for LFP/MCS at the high discharge rate of 20C remains stable whereas that for LFP does not. This demonstrates the efficient transport capability of Li ions into the nanoscale LFP shell in the core-shell structure of LFP/MCS, which is essential for the improvement of the electrochemical performance.