Kinetically-controlled formation of Fe2O3 nanoshells and its potential in Lithium-ion batteries

Abstract

• A wet chemical synthetic protocol was developed to build uniform Fe 2 O 3 nanoshells. • Hexamethylenetetramine was critical in modulating the precipitation kinetics. • This protocol was successful in building Fe 2 O 3 coatings around various substrates. • A nondestructive surface treatment could be achieved by this anhydrous protocol. • The cycling performance of LiNi 0.5 Mn 1.5 O 4 greatly improved after Fe 2 O 3 coating. The construction of uniform metal oxide nanoshells has been widely considered as an effective protocol for the protection of high energy cathodes in lithium-ion batteries. Solution-based synthetic routes have recently become feasible to build such protective shells, but are challenged by the incidental damage to cathodes since an acidic condition is usually needed to prevent the fast precipitation of active metal cations in aqueous solutions. Here, by switching to anhydrous solution, we demonstrate the possibility of creating Fe 2 O 3 nanoshells by taking advantage of the much-reduced ionic activity of Fe 3+ in ethanol without the involvement of corrosive environment. Hexamethylenetetramine is identified as an efficient growth controller, whose slow decomposition is critical to modulate the growth kinetics of the formed metal hydroxide precursor, forming core@shell structures with the shell thickness controlled at nanometer accuracy. This synthetic protocol is successful in building uniform Fe 2 O 3 coatings around various substrates, particularly LiNi 0.5 Mn 1.5 O 4 , a well-known high energy cathode whose applications are challenged by poor cycling performance related to the high working voltage. This surface treatment for LiNi 0.5 Mn 1.5 O 4 is effective in improving the electrochemical behavior of the cathode with a successful suppression of its structural degradation as well as a substantial improvement in its high temperature stability.