Increasing the Capacity of Nano-Structured LiMn2O4 Pseudocapacitors by Selective Crystallization of Dissolution Resistant Surface Facets

Pseudocapacitive materials are important for high power energy storage devices that can help meet the increasing need for mobile power. While good progress has been made in pseudocapacitive anode materials, less work has been done on fast charging cathodes. We have previously reported on nanoporous LiMn 2 O 4 as an exciting pseudocapacitive cathode, however, the capacity is compromised in nanosized LiMn 2 O 4 due to surface manganese dissolution. Here, we designed LiMn 2 O 4 with different nanostructures: round-LMO (R-LMO) and needle-like LMO (N-LMO) using two different precursors: acetate and nitrate salts, respectively. We examined the effect of this nanoscale structure on electrochemical performance and found that N-LMO displayed higher capacity than R-LMO, despite similar kinetics. Unlike the R-LMO which showed no preferred surface faceting, N-LMO was found to be dominated by (111) surface facets, which have been shown to be more resistant to surface manganese dissolution. XPS studies on the Li counter electrodes corroborated this idea, showing less manganese dissolution and replating on the counter electrode in the case of N-LMO. Together, this study provides insights into how surface structure affects the electrochemical properties of nanostructured LiMn 2 O 4 and presents a facile, low cost synthetic methodology for the production of a high performance pseudocapacitive cathode material.