Effect of carbon coating on the electrochemical performance of LiFePO₄/C as cathode materials for aqueous electrolyte lithium-ion battery

Organic electrolyte is widely used for lithium-ion rechargeable batteries but might cause flammable fumes or fire due to improper use such as overcharge or short circuit. That weakness encourages the development of tools and materials which are cheap and environmental friendly for rechargeable lithium-ion batteries with aqueous electrolyte. Lithium iron phosphate (LiFePO₄) with olivine structure is a potential candidate to be used as the cathode in aqueous electrolyte lithium-ion battery. However, LiFePO₄ has a low electronic conductivity compared to other cathodes. Conductive coating of LiFePO₄ was applied to improve the conductivity using sucrose as carbon source by heating to 600°C for 3 h on an Argon atmosphere. The carbon-coated LiFePO₄ (LiFePO₄/ C) was successfully prepared with three variations of the weight percentage of carbon. From the cyclic voltammetry, the addition of carbon coatings could improve the stability of cell battery in aqueous electrolyte. The result of galvano-static charge/discharge shows that 9% carbon exhibits the best result with the first specific discharge capacity of 13.3 mAh g−¹ and capacity fading by 2.2% after 100 cycles. Although carbon coating enhances the conductivity of LiFePO₄, excessive addition of carbon could degrade the capacity of LiFePO₄.