Intermittent Contact Alternating Current Scanning Electrochemical Microscopy: A Method for Mapping Conductivities in Solid Li Ion Conducting Electrolyte Samples

Abstract

Intermittent contact alternating current scanning electrochemical microscopy (ic-ac-SECM) has been used to determine the electrochemical response to an ac signal of several types of materials. A conductive gold foil and insulating Teflon sheet were first used to demonstrate that the intermittent contact function allows the topography and conductivity to be mapped simultaneously and independently in a single experiment. Then, a dense pellet of an electronically insulating but Li ion conducting garnet phase, Al-substituted Li7La3Zr2O12 (LLZO), was characterized using the same technique. The polycrystalline pellet was prepared by classical ceramic sintering techniques and was comprised of large (~150 μm) grains. Critical information regarding the contributions of grain and grain boundary resistances to the total conductivity of the garnet phase was lacking due to ambiguities in the impedance data. In contrast, the use of the ic-ac-SECM technique allowed spatially resolved information regarding local conductivities to be measured directly. Impedance mapping of the pellet showed that the grain boundary resistance, while generally higher than that of grains, varied considerably, revealing the complex nature of the LLZO sample.

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li7La3Zr2O12 garnets

“…LIBS measurements detected aluminium and lithium rich phases in the first micrometres before the elemental distribution returns to a more or less equilibrated state. In addition, also misorientation angles may affect the ionic conductivity [35]. This could also contribute to the lower local conductivities found here.…”

“…Possibly, local stoichiometric deviations near to the surface or the formation of impurity phases or secondary phases (e.g. La 2 Zr 2 O 7 , LaAlO 3 , La 2 O 3 , La(OH) 3 , Li 2 CO 3 , LiOH), are responsible for the lower nominal conductivities σ me [14,[33][34][35], since preparation as well as measurements include exposure to air. Hou et al investigated Al stabilized LLZO, sintered at 1100°C, by means of laser induced breakdown spectroscopy (LIBS) as a surface sensitive measurement method [36].…”

Enhanced lithium ion transport in garnet-type solid state electrolytes

“…Recent work on garnet conductors has been directed towards stabilizing the more conductive cubic polymorph [8,9] and improving total conductivity via, for example, partial or multiple substitutions [10][11][12][13][14], and/or grain boundary engineering [15][16][17] [18].…”

“…shows the Arrhenius plot of the total conductivities as a function of temperature of the two kinds of pellets. It was not possible to deconvolute bulk and grain boundary conductivities from the impedance data: see reference[15] for typical Nyquist plots of LLZO samples made in air. Total conductivities of the sample processed under Ar are higher than that of the sample prepared in air at every temperature that was measured.…”

Characterizing Batteries by In Situ Electrochemical Atomic Force Microscopy: A Critical Review

“…[ 291 ] Intermittent contact alternating current scanning electrochemical microscopy (ic‐ac‐SECM) demonstrated its effectiveness in measuring the ionic conductivity while obtaining the local topographic images of SSE. [ 292 ] Figure 14 a,b show the topographic and impedance maps obtained at a large LLZO grain using ic‐ac‐SECM over 250 × 250 µm. The grain is surrounded by boundaries of higher impedance.…”