An aqueous hybrid lithium ion capacitor based on activated graphene and modified LiFePO4 with high specific capacitance

Aqueous Li-ion capacitors (ALICs) have been extensively studied in recent years due to their safety, environmental friendliness and low availability. In this paper, we constructed an ALIC using carbon-coated lithium iron phosphate (LFP) as the positive electrode, activated reduced graphene oxide as the negative electrode and studied its electrochemical performance in 1 M Li2SO4 electrolyte. Here, coating of LFP particles is carried out by dopamine polymerization to form a uniform carbon layer on the surface of the particles, which increases the conductivity and cycle performance of LFP. The optimal ALIC can achieve 82.8 F g−1 (based on the total mass of the positive and negative materials) at a current density of 0.2 A g−1, and shows good cycling stability. The specific capacitance can still retain 73% of the initial value after 1000 charge and discharge cycles. The specific energy density can reach 11.5 Wh kg−1 at a power density of 100 W kg−1.