Suppression of atom motion and metal deposition in mixed ionic electronic conductors

Abstract

Many superionic mixed ionic–electronic conductors with a liquid-like sublattice have been identified as high efficiency thermoelectric materials, but their applications are limited due to the possibility of decomposition when subjected to high electronic currents and large temperature gradients. Here, through systematically investigating electromigration in copper sulfide/selenide thermoelectric materials, we reveal the mechanism for atom migration and deposition based on a critical chemical potential difference. Then, a strategy for stable use is proposed: constructing a series of electronically conducting, but ion-blocking barriers to reset the chemical potential of such conductors to keep it below the threshold for decomposition, even if it is used with high electric currents and/or large temperature differences. This strategy not only opens the possibility of using such conductors in thermoelectric applications, but may also provide approaches to engineer perovskite photovoltaic materials and the experimental methods may be applicable to understanding dendrite growth in lithium ion batteries.

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…Copyright 2014, Wiley‐VCH. b) Critical electric current density ( J c ) and c) critical electric potential difference ( V c ) of Cu 1.97 S as a function of the L material . d) Relative electrical resistance variation ( R/R 0 , R is the concurrent electrical resistance and R 0 is the initial electrical resistance) as a function of J for Cu 2 Se and Cu 2− x S ( x = 0, 0.03, 0.04, 0.06, and 0.1) legs with the material length ( L material ) of 10 mm …”

“…Qiu et al developed a theoretical model to investigate the diffusion of Cu ions in the superionic α‐phase of Cu 2 X and the corresponding . Historically, it is believed that the critical parameter of Cu protrusion in Cu 2 X is the electric current density ( J ).…”

“…When J reaches the critical level ( J c ), Cu protrusion occurs . To confirm whether J c is the real critical parameter, taking Cu 1.97 S as an example, Qiu et al measured both the J c and the critical electric potential difference ( V c ) as a function of the material length ( L material ) under which condition that one Cu 2 X leg is composed of an entire material as shown in Figure b,c, respectively. As V c = J c ⋅L material /σ , if J c is the critical parameter, V c should be L material ‐dependent.…”

“…Under the isothermal condition, V c , can be expressed as where z e , F , Δ μ Cu crit , R , K e , x , and x c are the charge definition factor (−1 for electrons and +1 for holes), Faraday's constant, critical chemical potential difference between the Cu protrusion and the Cu 2 X at which level the Cu protrusion can happen, the gas constant, equilibrium constant for electrons and holes (independent of Cu off‐stoichiometry), Cu off‐stoichiometry level in Cu 2− x X and critical Cu off‐stoichiometry level, respectively. Hence, increasing x (i.e., introducing Cu vacancies) can reduce V c and increase the stability of Cu 2− x X.…”

Copper chalcogenide thermoelectric materials

“…Most recently, we have studied the mechanism of Cu migration in liquidlike materials and found it is possible to greatly improve material's stability by introducing electronically-conducting but ion-blocking barriers [104]. Similarly, Tang et al [105] found that the incorporated graphene three dimensional (3D) network can provide another possibility to block the migration of Cu ions and to enhance the stability of Cu 2 S.…”