In Situ Electrical Conductivity of Li_xMnO₂ Nanowires as a Function of x and Size

Abstract

Manganese oxide, MnO 2 , excels as a hybrid electrical energy storage material: The manganese centers in MnO 2 are capable of undergoing a reduction from 4+ to 3+ balanced by the intercalation of lithium ions to form Li x MnO 2 while its conductive surfaces simultaneously store energy as an electrical double layer capacitor. The highest capacitance and power performance for MnO 2 has been obtained for ensembles of nanowires that are 200 nm or less in width and many microns in length. Typically such MnO 2 nanowires are attached to a current collector at just one end, and electrical conductivity of the nanowire is therefore required in order to maintain a consistent redox and charge state along its axis. The electrical conductance of the nanowire therefore plays a very important role, and yet this parameter has been measured in few previous studies. In this work, we directly measure the electrical conductance of δ-MnO 2 nanowires in situ in 1 M LiClO 4 , acetonitrile as a function of the equilibrium Li content for nanowires with varying lateral dimensions. This measurement is accomplished using arrays of 200 MnO 2 nanowires that are 40−60 nm in height and 275−870 nm in width and which span a 10 μm gap between two gold contacts. Nanowires of fully oxidized MnO 2 are first prepared at +0.60 V vs MSE in acetonitrile. As the equilibrium electrode potential is decreased from 0.60 V to −0.80 V and lithium is intercalated, the electrical conductivity of MnO 2 nanowires increases by up to 1 order of magnitude. The measured change in conductivity is dependent on the equilibrium potential, which in turn is related to the Li content, and also depends on the width of nanowires. After doping at −0.80 V vs MSE, the conductivity increases by 30% for a 870 nm wide nanowire array and 880% for a 275 nm wide nanowire array. TEM investigations implicate the nanowire porosity in this difference.

Redox properties of birnessite from a defect perspective

“…are elongated by about 13%. A small polaron usually results in a low electrical conductivity due to the small-polaron hopping conduction, and our calculation helps to explain the extremely low electrical conductivity of birnessite MnO2 nanowires reported recently (27).…”

High-Performance Flexible All-Solid-State Asymmetric Supercapacitors Based on Vertically Aligned CuSe@Co(OH)2 Nanosheet Arrays

“…[5][6][7][8] They are very stable during the charge/discharge (CD) process, but suffer from relatively low specific capacitances. The other kind is transition metal oxides/hydroxides, such as MnO2, [9][10][11][12][13][14][15] RuO2, [16][17][18][19] Co(OH)2 [20][21][22][23] et.al., the energy stored by reversible Faradic reactions occurring at the electrode surface. They have high theoretical capacitance, whereas their electrical conductivity and mechanical properties are poor.…”

The reaction current distribution in battery electrode materials revealed by XPS-based state-of-charge mapping

“…Please do not adjust margins Please do not adjust margins electronic conductivity [30][31][32] during ion insertion or deinsertion, though this is not often incorporated into battery models. Nevertheless, if the average conductivity is known, the parameter ષ should provide a rough guideline for achieving mostly homogeneous RCDs in 1D electrode structures with limited electrical contact to the current collector, such as nanowire arrays or other similar microarchitectures under development.…”