Nanocrystalline LiMn2O4 derived by HMTA-assisted solution combustion synthesis as a lithium-intercalating cathode material

Nanocrystalline LiMn2O4 was synthesized by a self-sustaining solution combustion method with hexamethylenetetramine as a fuel. Ammonium nitrate was used as an additional oxidant-and-porogen. Thermal analytical studies showed the formation of LiMn2O4 by a single-step decomposition process between 300 and 380 °C. The products were highly crystalline with an average crystallite size of ∼30 nm. Charge–discharge studies showed that the optimal heat treatment protocol was a 10 h calcination at 700 °C. A product obtained under these conditions from a precursor containing a 1:1 molar ratio of [LiNO3 + Mn(NO3)2] and NH4NO3 sustained 202 cycles between 3.0 and 4.3 V at a charge–discharge rate of 0.1 C before reaching an 80% charge retention cut-off value. Nanocrystalline particles provide small diffusion pathways that lead to an improvement in the lithium-ion intercalation kinetics and minimize surface distortions during cycling. These factors are believed to confer excellent electrochemical properties to the product.