Pressure Dynamics in Metal–Oxygen (Metal–Air) Batteries: A Case Study on Sodium Superoxide Cells

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• 作者：Pascal Hartmann ; Daniel Grübl ; Heino Sommer ; Jürgen Janek ; Wolfgang G. Bessler ; Philipp Adelhelm
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：1461-1471
• 全文大小：501K
• ISSN：1932-7455

文摘

Electrochemical reactions in metal鈥搊xygen batteries come along with the consumption or release of gaseous oxygen. We present a novel methodology for investigating electrode reactions and transport phenomena in metal鈥搊xygen batteries by measuring the pressure dynamics in an enclosed gas reservoir above the oxygen electrode. The methodology is exemplified by a room-temperature sodium鈥搊xygen battery forming sodium superoxide (NaO₂) in an electrolyte of diethylene glycol dimethyl ether (diglyme) and sodium trifluoromethanesulfonate (NaOSO₂CF₃, NaOTf). The experiments are supported by microkinetic simulations with a one-dimensional multiphysics continuum model. During galvanostatic cycling over 30 cycles, a constant oxygen consumption/release rate is observed upon discharge/charge. The number of transferred electrons per oxygen molecule is calculated to 1.01 卤 0.02 and 1.03 卤 0.02 for discharge and charge, respectively, confirming the nature of the oxygen reaction product as superoxide O₂^{鈥?/sup>. The same ratio is observed in cyclic voltammetry experiments with low scan rate (<1 mV/s). However, at higher scan rates, the ratio increases as a result of oxygen transport limitations in the electrolyte. We introduce electrochemical pressure impedance spectroscopy (EPIS) for simultaneously analyzing current, voltage, and pressure of electrochemical cells. Pressure recording significantly increases the sensitivity of impedance toward oxygen transport properties of the porous electrode systems. In addition, we report experimental data on the diffusion coefficient and solubility of oxygen in electrolyte solutions as important parameters for the microkinetic models.}