Effects of liquid-phase carbon combining surfactant coatings on the performance of LiMn0.2Fe0.8PO4 cathode materials

Efforts to reduce the particle size of LiFe x Mn 1- x PO 4 materials and apply conductive carbon coatings have yielded substantial benefits in terms of obtaining lithium-ion batteries (LIBs) with enhanced electrochemical performance. However, LiFe x Mn 1- x PO 4 materials with small particle sizes and uniform carbon layers cannot be obtained by the conventional high-temperature solid-phase method, which is the most convenient and applicable method for the industrial-scale preparation of the cathode materials used in commercial LIBs. The present work addresses this issue by applying the cationic surfactant cetyltrimethylammonium bromide (CTAB) in conjunction with LiMn 0.2 Fe 0.8 PO 4 (LMFP) particles, and obtaining a carbon layer by replacing the conventional in-situ solid-phase carbon coating process with a secondary liquid-phase coating process using sucrose as the carbon source. The CTAB surfactant is observed to be uniformly adsorbed on the surface of LMFP particles, and maintains small LMFP particle sizes by operating as a dispersant preventing their agglomeration. Additionally, the carbon network formed by CTAB pyrolysis acts as an intermediate medium ensuring that the conductive carbon layer is uniformly and firmly adhered to the LMFP particle surfaces at a high preparation temperature of 680°C. This composite carbon layer is demonstrated to enhance lithium-ion transport, while concurrently acting as a barrier interfering with manganese diffusion within the electrolyte during charge-discharge cycling. As a result, the optimal LMFP-based cathode material achieves reversible specific capacities of 160 mAh g −1 and 120 mAh g −1 at charge-discharge rates of 0.1 C and 5 C, respectively, and the capacity retention is 88 % after 500 cycles at 1 C. Hence, the results verify that the proposed surfactant-mediated liquid-phase carbon coating process is an effective method for enhancing the overall electrochemical performance of LMFP-based cathode materials. • Reduction of LMFP particle size using surfactant CTAB. • Liquid-phase carbon combined with surfactant coating inhibits Mn dissolution. • LMFP@CTAB/C(L) reversible specific capacity up to 160 mAh g −1 at 0.1 C. • the capacity retention of LMFP@CTAB/C(L) is 88 % after 500 cycles at 1 C.