Synthesis of carbon-coated LiMn0.8Fe0.2PO4 materials via an aqueous rheological phase-assisted solid-state method

Constructing a 3D Interconnected Carbon Network for Mg-Doped Porous LiMn0.85Fe0.15PO4/C Cathode Materials

Economical and high-safety LiMn0.85Fe0.15PO4/C cathode materials have gained significant attention recently due to their theoretical specific energy advantage of 18% compared to LiFePO4. However, their low electronic conductivity and sluggish diffusion kinetics limit the practical applications of LiMn0.85Fe0.15PO4/C. This paper presents a simple solid-state synthesis of porous LMFM0.01P-2C4P, which is doped with Mg and coated with composite carbon. Mg substitution for Mn shortens the transport path of lithium ions while increasing intrinsic conductivity and structural stability. Additionally, a 3D conductive network structure generated by the composite carbon source (citric acid and polyethylene glycol 400) improves the electronic conductivity and effectively minimizes the internal resistance of the battery. LMFM0.01P-2C4P consists of secondary particles aggregated from primary particles smaller than 100 nm, each of which is coated with a uniform carbon layer. The electronic conductivity and lithium-ion diffusion coefficient greatly exceed those of unmodified LMFP-4C, measuring 7.22 × 10-3 S cm-1 and ∼10-12 cm2 s-1, respectively. Electrochemical studies demonstrate that LMFM0.01P-2C4P delivers a superior specific capacity of 152.1 m Ah g-1 and 124.9 m Ah g-1 at 0.1C and 1C, respectively, along with a capacity retention of 80.8% after 500 cycles at 1C. However, the initial capacity of LMFP-4C is merely 104.1 mAh g-1 at 1C, with a capacity retention of only 65.7% after 500 cycles. This work presents a useful way to enhance the conductivity of phosphate cathode materials for lithium/sodium-ion batteries.

Study on the Preparation and Electrochemical Properties of LiFe0.4Mn0.6PO4 Coated with Bamboo Shaving-Based Carbon

LiFe1-xMnxPO4 (0 < x < 1) has a high operating voltage range and theoretical energy density, but its actual capacity decreased due to its low electronic conductivity. To overcome this problem, we successfully prepared LiFe0.4Mn0.6PO4/C (LFMP/C) with a uniform carbon coating by a one-step solvothermal method using bamboo shavings as the carbon source. The results showed that heating at a reaction temperature of 180 °C for 18 h was the optimal synthesis condition to obtain LFMP/C. The addition of bamboo shaving-based carbon was effective in inhibiting excessive grain growth and reducing particle size. The disordered carbon layer enhanced the surface conductivity by connecting the surfaces of the particles. The synergistic effect of the nanoparticle size and the pores distributed around the particles increased the specific surface area and thus improved the contact area between the active substance and the electrolyte. Furthermore, there were improvements in electronic conductivity and ionic mobility. LFMP/C-16 showed initial discharge capacities of 150.1 and 143.5 mAh·g-1 at rates of 0.1 and 0.2C, respectively, with a capacity retention rate of 97.73% after 100 cycles, indicating excellent cyclic performance.