Preparation Of Carbon-Coated Lithium Iron Phosphate As Lithium-Ion Battery Cathode Material And Electrochemical Performance In Aqueous Electrolyte

Compared with traditional rechargeable lithium-ion battery with organic electrolytes, the aqueous rechargeable lithium-ion battery (ARLB) is one of the most potential energy storage systems due to its low cost, environmental benignness, high efficiency and safety. LiFePO4 has been studied as a promising cathode material applied in ARLB owing to its environmental friendliness, higher safety, lower cost and good electrochemical property in aqueous electrolyte. However, the lower electronic and ionic conductivity of LiFePO4 lead to poor electrochemical performance. In order to overcome those problem, many strategies have been proposed, such as coating carbon, doping with ion and tailoring particle size.In our work, a precursor has been prepared through a simple method. Then we mix the precursor with carbon source and calcinate the mixture in N2 atmosphere. The electrochemical property is carried out in the aqueous electrolyte through a three-electrode cell. The main contents are listed as following:1. The different precursors of LiFePO4 are prepared through a simple one-pot two-step precipitation method. The effects of preparation parameters on precursors’ morphologies are investigated. We find the precusor is uniform microdisk when the final composition of reaction system is 0.6 mol·L-1 LiOH,0.2 mol·L-1 FeSO4,0.2 mol·L-1 H3PO4,0.02 mol·L-1 AA and 0.04 mol·L-1 PVP at 100℃ for 3h. Subsequently, we synthesize the LiFePO4/C with exposed (010) planes by heating the mixture of precursor and carbon source in N2 atmosphere.2. We synthesize the precursor through a simple one-pot method with zero-valent iron as iron source. Firstly, the iron react with the mixture of nitric acid and acetic acid for 4h. Then the phosphoric acid and lithium hydroxide are added into suspension and go on reacting for preparing precursor. The LiFePO4/C is synthesized through calcinating the mixture of PVP and precusor. Its structure and morphology are characterized by XRD and SEM. This method is promising for industrial application.3. Electrochemical property is tested in a Li2SO4 aqueous solution using a three-electrode cell. We use the LiFePO4/C as working electrode, saturated calomel electrode(SCE) and Pt foil are reference and counter electrode, respectively. The result reveals that the microdisc-shaped LiFePO4/C with exposed (010) planes shows good initial discharge capacity and stability. Its initial discharge capacity is 127 mAh·g-1 at 0.25C. The capacity retention is 98% and 80% after 80 and 200 charge-discharge cycles, respectively. The LiFePO4/C prepared with zero-valent iron as iron source exhibits a reversible capacity of 109mAh·g-1 at 0.25C when the carbon centent is 6.47%.