The gelation of commercially available lithium iron phosphate (LiFePO4) in water-based slurry and its corresponding mechanism are studied. Based on surface chemistry analyses using zeta potential measurements and Fourier transform infrared spectroscopy, it is found that the key factor that causes LiFePO4 gelation in the aqueous slurry is the quality of the surface carbon coating on powder. When the surface carbon exhibits functional derivatives, such as carboxyl, hydroxyl, and carbonyl polar functional groups, LiFePO4 tends to form a three-dimensional, gel-like structure via hydrogen bonding. Moreover, the presence of the derivatives reduces the amount of conduction-favorable sp(2)-bonded carbon to LiFePO4, resulting in an electric resistance increase of the as-prepared electrode and the deterioration of the specific capacity of the as-constructed cell. (C) 2016 Elsevier B.V. All rights reserved.